BOUGHT WITH THE INCOME f^OM THE SAGE ENDOWMENT FUND THE GIFT OF Henrg W. Sage 3 1924 031 240 439 The original of tliis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924031240439 ELECTEIGAL EXPERIMENTS. BONNEY. INDUCTION COILS. A Practical Manual for Amateur Coil Makers. By G-. E. Bonnet. 101 Illustrations. Square crown 8vo, 3s. *'In Mr. Bonney's useful book, every part of the coil is described minutely in detail, and the methods and materials required in insulating and winding the wire are fully con- sidered.*' — ElectHcal Review. ''Written in a clear and attractive style, the book may bo understood by the veriest tyro in electrical matters." — Electrician. "An excellently illustrated volume, written in clear and concise language." — Science mid Art. " We heartily commend the book." — Electricity. " The instructions are very clearly written." — Star. "Mr. Bonney has done his work well and fully." — Eclio. "A thoroughly reliable and scientific treatise.'* — Speaker. THE ELECTRO-PLATER'S HANDBOOK. A Practical Manual for Amateurs and Young Stu- dents in Electro-Metallurgy. By G. E. Bonnet. With FuU Index and 61 Illustrations. 3s. CowTHHTS: — I. Blectro-Deposition of Metal — II. Electro- Deposition by Current from Batteries — III. Dynamo- Electric Plating Machines— IV. Electro-Platers' Materials —V. Preparing the Work— VI. Electro-Plating with Silver —VII. Gold— VIII. Nickel-lX. Copper— X. Alloys— XI. Zinc, Tin, Iron, etc. "An amateur could not wish for a better exposition of the elements of the subject. . . . The work has an excellent index and sixty-one illustrations, and will form a useful addition to Messrs. Whittaker's valuable series of. practical manuals."- JElectrical Review* "The work is of evident utility, and has before it a future.*'- C7iemicat News. "It contains a large amount of sound information."— Natvre. "Well suited to the requirements of the class for which it is written."— Dail|/ Chronicle. " A book suited for any inquiring workman in the gild- ing and silvering trades."— Jeweller arid Metal Worker. ' A bandy little book— valuable to the amateur electro- plater and to many in business also.'*— Eugmeer. ELECTRICAL EXPERIMENTS, H Manual of instructive Hmusement. G. E. BONNEY, Author of " The Electro-plater's Handbook," " Induction Coils," etc. WITH 144 ILLUSTRATIONS. LONDON : WHITTAKER & CO., PATERNOSTER SQUARE, E.G. And 112, Fotjeth Atentje, New Yobk. BUTLES & TaWKER, The Selwood Printing Wobks, Fbome, and Loitdon. PREFACE. This book is written in response to suggestions received from correspondents, and hints given in letters sent to the Editor of Work, that I should write a book showing how Induction Coils and other electrical apparatus can be used for instructive amusement. My correspondents state that a large number of idle hours hang wearily on the hands of youths during the long winter evenings in country villages, which could be spent in profitable amusement if they only knew how to use easily-made electrical apparatus. In the following pages I have shown how to derive amusement from instruments made at liome from materials obtained at little cost, com- mencing with the homely sixpenny horseshoe magnet, the toy of every schoolboy. As a description in detail of every instrument would have occupied too much space in this book, and has been fully given in other volumes issued by the pub- lishers, I have referred readers to those books, wherein vi PREFACE. they will find full illustrated instructions for making Induction Coils, Batteries, Dynamos, and other elec- trical instruments. Induction Coils and galvanic batteries are fully described and illustrated in the author's book on this subject, price 3s. Machines for generating a static current of electricity are described in Electrical Influence Machines, price 4s. Qd. Electric Bells, and All About Them, price 3s., will tell how electric bells are made. The Electro-plater's HandhooJc (price 3s.) will give instruction in making apparatus and solutions used in electrolytic experiments. Dynamos, Telephones, Electromotors, G-alvanometers, and other electrical in- struinents are described and illustrated in Electrical Instrument Making for Amateurs, price 3s. ; Electricity in our Homes and Workshops, price 5s. ; Electro- Motors : How Made and How Used, price 3s. ; and the Telephone HandhooTc, price 3s. &d. When the cost of books and of instruments is likely to exceed the means of any one experimenter, it will be advisable for several persons to form a club or class for amusement, and purchase the books and material from a common fund, to which all subscribe. Clergymen, schoolmasters, and others interested in the education and welfare of the youth in our country districts, could do good service by organizing such clubs. The author hopes that the members of such clubs will not be con- PBEFAOE. vii tent to merely find amusement for leisure hours in per- forming the experiments mentioned in this book, but will go on from this to something higher^ filling the mind as it expands with useful knowledge, and seeking to know the why and the wherefore of all the observed results of those experiments. As aids to the study of Magnetism and Electricity as a science, I can highly recommend Maycock's " First Book on Electricity and Magnetism," price 2s. 6d., and Bottone's new book on the same subject, both published by Messrs. Whittaker & Co. CONTENTS. I. Magnetic Experiments II. Experiments with Electro-Ma&nets III. Experiments with Induction Coils IV. Experiments with Static Electricity V. Electrolytic Experiments VI. Miscellaneous Electrical Experiments INDEX TO SECTIONS. SECTION 1. Magnets and Magnetism 2. Experiments witli the Lodestone . 3. Permanent Magnets 4. Making Permanent Magnets . 5. Magnetizing by Single Touoli 6. Magnetizing by Double Touch. 7. Magnetizing by Electric Induction 8. Lines of Magnetic Force 9. Magnetic Repulsion 10. Mayer's Magnetic Floating Needles 11. Magnetic Boats, Fishes, and Birds 12. Magnetic Suspension 13. Magnetic Induction 14. Miscellaneous Magnetic Experiments IB. Uses of Permanent Magnets . 16. Relation of Magnetism to Electricity 17. Simple Electro-Magnets 18. Horse-shoe Electro Magnets . 19. Electro-Magnetic Portation . 20. Electro-Magnetic Solenoids . 21. Magic Magnetic Rings . 22. Magic Magnetic Hemispheres 23. Uses of Electro-Magnets 24. Spark Induction Coils . 25. Experiments with Spark Induction Coils 26. Experiments with Henley's Discharger 27. Lighting Gas by Electricity . 28. Electric Fuses PAGE 1 2 4 7 9 12 13 17 20 23 24 27 30 32 84 40 51 52 55 58 63 65 66 68 70 70 83 85 INDEX TO SECTIONS. SECTION 29. Decomposition Experiments .... BO. Charging Leyden Jars from a Coil 31. Experiments with Electric Sparks in Vacuo 32. Vacuum Tubes 33. Tesla's Experiments with Vacuum Tubes . 34. Rotating Vacuum Tubes .... 85. Other Experiments with Vacuum Tubes 36. Physiological Effects from Induction Coils . 37. The Production of Static Electricity 38. Simple Producers of Electricity . 39. Indicators of Static Electricity 40. Experiments with Electroscopes . 41. The Electrophorus .... 42. How to Use an Electrophorus 43. Experiments with the Electrophorus 44. Leyden Jars 45. Experiments with Leyden Jars 46. Condensers of Electricity 47. Electrical Machines 48. "Working Electrical Influence Machines 49. Charging Leyden .Jars from an Electrical Machine 50. Experiments with Electrical Machines 51. Remarks on Electro-Static Experiments 52. Electrolysis 53. Electric Current required for Electrolysis 54. Electrolysis of Water 55. Electrolysis of Coloured Fluids 56. Electrolysis of Metallic Salts . 57. Simple Electro-Deposition of Metals 58. Single Cell Electro-Deposition of Metals 59. Electrotype Experiments 60. Electro-Deposition of Metals 61. Thermo-Electrical Experiments 62. Electric Light Experiments . 63. Electric Amalgams and Cements 64. Guides to Electric Experiments General Index .... LIST OP ILLUSTRATIONS. FlO. PAGB 1. Lodestone 2 2. Iron Filings Attracted to Magnetized Steel ... 4 8. A Horse-shoe Magnet and Keeper .... 7 i. A Compound Horse-shoe Magnet 7 5. Bar Magnets Arranged for Storage .... 7 6. Magnetizing Steel Bar by Single Touch ... 10 7. Magnetizing Steel Bar with Horse-shoe Magnet . . 11 8. Arrangement of Horse-shoe Magnets . . . .11 9. Magnetizing Steel by Double Touch .... 12 10. Duhamel's Method of Magnetizing Steel ... 13 11. Split Bobbin for Coil of Wire 15 12. "Wire Coil for Magnetizing Steel 16 13. Lines of Magnetic Force. Bar Magnet ... 18 14. „ „ „ Horse-shoe Magnet . . 18 15. „ „ „ Over „ „ . . 19 16. „ „ „ Around Poles of Magnets . 19 17. Effects of Breaking a Magnet 20 18. Wooden Gallows for Suspending Magnets ... 21 19. Stirrup to hold Suspended Magnets .... 22 20. Mayer's Magnetic Needles 24 21. Inductive Action of Bar Magnet 81 22. Magnetized Needle Balanced on a Pivot ... 36 23. Section of Compass Box 37 24. Portable Boat Compass 38 25. The Dipping Needle 38 26. Magnetic Shell around an Electric Conductor . . 41 27. Magnetized Filings around a Wire .... 41 28. Magnetized Filings over a Wire 41 xiv LIST OF ILLUSTRATIONS. FIG. 29. Horizontal Gralvauometer 30. Shell of Iron Filings around a Line "Wire 31. Testing the Sphere of Magnetic Influence 32. Oersted's Induction Apparatus 33. Ampere's Stand and Rectangle 34. Diamagnetic Experiment with Copper Cube 35. Diamagnetic Experiment with Candle . 36. 37. Paramagnetic and Diamagnetic Fluids 38. Simple Bar and Horse-shoe Electro-Magnets 39-41. Varieties in Forms of Electro-Magnets . 42. Electro-Magnet with Wire Heaped on the Poles 43. Powerful Electro-Magnet on Stand 44. Tripod for Suspending Magnets 45. Bowron's Electric Hammer .... 46. Apparatus for showing the Magnetic Poles of a Solenoid 47. Professor Bain's Helix Experiment 48. Divided Iron Ring 49. Magic Magnetic Ring 50. Magic Magnetic Sphere 51. Section of Magic Magnetic Hemisphere 52. King, Mendham & Co.'s Electro-Motor . 53. A Spark Induction Coil 54. Henley's Discharger for Spark Coils 55. Bent Wires on Ends of Fixed Discharger 56. Apparatus for Producing Sparks under Water . 57. Lichtenberg Dust Figure 58. 59. Negative and Positive Dust Figures 60. Electric Gas-Lighter 61. Electric Fuse 62. Apparatus for Decomposing Water 63. Experiments with the Electric Egg 64. Gassiot's Cascade 65. Appearance of Striee in a Straight Vacuum Tube 66. Various Forms of Vacuum Tubes .... 67. Appearance of Striae in a Contracted Vacuum Tube 68. Various Forms of Vacuum Tubes .... 69. Varieties in Geissler Tubes .... LIST OF ILLUSTRATIONS. xy «»• PAGE 70. Ornamental G-assiot Tubes on Stands . . . .106 71. Gassiot Star Hand Eotator Ill 72. 73. Electric Ring Rotators 112 74. Electric Rotator with Crank Motion . . . 113 75. Bowron's Electric Eotator 114 76. King, Mendham & Co.'s Electric Fan . . . .116 77. Effects of Magnets on the Strise in a Vacuum Tube . 116 78. Professor Henry's Induction Experiment . . . 119 79. Mounted Coils for Use in Prof. Henry's Experiment . 120 80. An Electrified Rod of Sealing-wax .... 123 81. Gold-Leaf Electroscope 127 82. Coulomb's Torsion Balance . . ... 129 83. Henley's Pith-Ball Quadrant 130 84. Pith-Ball Electroscope 181 85. Insulating Stool 137 86. Electrophorus 138 87. Proof Plane 141 88. Insulated Hollow Sphere 142 89. Blot's Experiment with Charged Hemispheres . . 143 90. Insulated Butterfly Net 144 91. Insulated Metal Cup and Electroscope .... 145 92. Involved Insulated Metal Cups 146 93. Insulated Ball and Cylinder 147 94. ExperimentwithlnsulatedCylinderandElectrophorus 148 95. Insulated Cone 149 96. Leyden Jar 151 97. Battery of Leyden Jars 152 98. Spotted Leyden Jar 153 99. High Insulation Leyden Jar ... . . 153 100. Leyden Jar with Movable Coatings .... 154 101. 102. Methods of Charging Leyden Jars in Cascade . 157 103. Lane's Electrometer 158 104. Harris' Unit Jar Electrometer 159 105. Leyden Jars on a Tinfoiled Base 160 106. Discharging Tongs 162 107. Discharging a Leyden Jar 164 108. Discharging Insulated Leyden Jar .... 165 xvi LIST OF ILLUSTRATIONS, me. 109. Henley's Universal Discharger 110. Electrical Chimes . 111. Electric Mortar . 112. Insulated Cup 113. Glass or Caj-d Piercer 114. Isulated Table 115. Thunder-House 116. Static Magnetizer . 117. Section of Fulminating Pane 118. Discharging a Fulminating Pane 119. Wimshurst Electrical Influence Machine 120. Arrangement of Tinfoil Specks on a Spangled 121. Spangled Tube 122. Luidinous Pane . 123. Aurora Flask 124. Clark's Patent Statical Electric Gas-Lighter 125. Kinnersley's " Electric Thermometer " 126. Electric Whirl 127. The Electric Orrery . 128. Appa,ratus for Electric Dancers 129. Electric Chimes . 130. Dummy Head of Hair . 131. U-Tube Voltmeter . 132. Voltmeter on Stand 133. Section of Voltmeter . 134. Sectional Elevation of a U-Tube 135. Wine-glass Experiment 136. Single-Cell Apparatus for Electrotype 137. Electrotyping Apparatus 138. Thermo-Electrio Pair . 139. Thermo-Electric Pair and Indicator 140. Arc Light Regulator . 141. „ „ . . . 142. Small Arc Lamp .... 143. Bowron's Semi-Incandescent Lamp 144. Incandescent Electric Lamp Tube. ELECTEICAL EXPERIMENTS, CHAPTEE I. EXPEKIMENTS WITH MAGNETS. § 1. Magnets and Magnetism. A magnet is a sub- stance having the power of attracting iron to itself through air-space, and adhering to iron by the same power of attraction. This power is named magnetism. Its cause is not known ; its nature, so to speak — that is, what its composition may be — is but faintly understood even by the high priests of science ; but its mode of action ailid the laws which govern this action, are more clearly known, and the knowledge is widely distributed. Magnets may be divided into two classes : — 1 . Natu- ral magnets. 2. Artificial magnets. The latter may be subdivided into two more; viz., (a) Permanent magnets, and (6) Electro-magnets. Natural magnets are masses of magnetic iron ore found abundantly in Sweden and Norway, and widely distributed through other parts of the world in the older geological for- mations. Its chemical composition may be expressed by the formula Fe^ O4, that is to say, there are three atoms of {fermm) iron combined with four atoms of 1 B 2 ELEGTBIOAL EXPERIMENTS. oxygen to form a molecule of the ore. lbs property of attracting iron was known to men in early ages of the worldj and is said to have been discovered in Magnesia, a district in Asia Minoi-, its name being derived from this discovery. The name of lodestone has also been Fig. 1. Lodestone. given to it, because of its property of placing itself with its ends pointing north and south, when suspended by a filament and free to move, the name being derived from the Saxon word " loadan," meaning " to lead," because this stone leads or guides the way to the north. Permanent artificial magnets are masses of steel made magnetic by charging them with magnetism, and "Electro-magnets are masses of iron made magnetic by the inductive influence of an electric current passing through wire wound over and around them. In subse- quent sections of this chapter we shall illustrate by means of experiments some of the wonderful effects of magnetism. § 2. Experiments with the Lodestone. As some of my readers may have specimens of magnetic iron EXPERIMENTS WITH MAGNETS. 3 ore, named lodestones, and may wish to try some simple experiments wifch tlie specimens, I will give a few hints for this purpose. Specimens are some- times found in cabinets of old curios, the stones being mounted in rectangular or square cases of brass or of silver, beautifully chased and furnished with a cheek and armature of iron. Many of the simple experiments detailed in subsequent sections under the heads of experiments performed with permanent magnets, may also be performed with a natural lodestone. These will not be repeated here, but will receive attention later on. One experiment only, peculiar to the lodestone, may be here described, because it cannot be performed with any other mineral specimen. The lodestone is the only stone capable of imparting a magnetic charge to a mass of steel such as a small steel bar. This may be done in the following manner : — Procure a bar of best shear or tool steel, 4 inches in length, ^-inch in width, and J- inch in thickness. Let it be ground smooth and true to give it a finished appearance, then heated to a bright red, and plunged suddenly in cold water to harden the steel. Clean the bar with a piece of emery cloth, and lay it on a level bench or table. Now take the lode- stone and stroke the steel bar with one end of it, always placing the same end of the lodestone on the centre of the bar, and stroking that half only in one direction. After stroking one-half of the steel in this way for several times, reverse the ends of the bar and of the lodestone, and stroke the reverse end in a similar manner. This experiment, if carefully done, will 4 ELEOTBICAL EXFEBIMENTS. impart a charge of magnetism to the steel bar, and this can be proved by stirring a heap of iron filings with the bar, or sprinkling a few iron filings on the ends. If the steel has been magnetized, it will attract and hold the iron filings, as shown at Fig. 2. If iron filings Fig. 2. Iron Filings Attracted to Magnetized Steel. are not to hand, the experiment may be pei-formed with iron brads, or iron tacks, or bits of iron wire. § 3. Permanent Magnets. When a piece of steel is charged with magnetism, it does not readily part with the charge, but retains the magnetic charge for an indefinite length of time. Hence, a bar of steel charged with magnetism, is named a permanent magnet. This term is generally correct for most practical pur- poses ; but a series of observations, extending over several years, has conclusively demonstrated that the very best permanent magnets gradually lose their strength and become weaker with age. This leakage EXPERIMENTS WITH MAGNETS. 5 of magnetism is nearly allied to tlie leakage of a static charge of electricity, as when a charged Leyden jar gradually loses its charge by leakage into the surround- ing air. The close resemblance between a magnetic charge and a static charge of electricity, as shown by this tendency to leakage, coupled with the property, common to both, of possessing opposing polarities, and a capability of imparting a charge to other bodies, has led some advanced thinkers to associate the two forces of magnetism and electricity in one. Mr. Spragae says of them : " Electricity and magnetism are the same force, and are two actions of polarized molecules, manifested at right angles to each other, and both developed together. Electricity is the action which occurs in the line of polatn^ation. Magnetism is the action which occurs at right angles to the line of jpolarha- tion, and in all directions at right angles to that line. But there are some important distinctions to be noticed. Electricity is essentially a dynamic force; its nature consists in producing motion in, and transmitting energy along, the polarized chains ; its static actions are only incidents of this pi'ocess, dependent on the resistance offered to the completed motion. Magnetism is, on the other hand, purely static ; it consists in the storing up of energyin the polarized molecules." Another distinction exists, which must be noticed here. Magnetic charge can only be taken up and retained by a few substances, such as iron, steel, nickel, and cobalt; but electric charge is capable of being received and conveyed by a larger number of substances. Soft iron can be highly 6 ELEOTEIOAL EKPEBIMENTS. magnetized, but is not capable of retaining a magnetic charge. Hard iron will receive and retain a magnetic charge, but its capacity for receiving the charge is less than that of soft iron, and its capability of retaining the charge is less than that of steel. Nickel and cobalt are only feebly magnetic. Hardened steel, such as cast tool steel, may be highly magnetized, and will retaiii the magnetic charge for a great length of time, if not subjected to rough usage. The best permanent magnets are made of the best steel, manufactured from Swedish iron, and must be equally tempered or hardened throughout. "Tung- sten steel" has also been recommended for magnets. Nothing whatever is gained by having a thick magnet made of a thick steel bar. The best effects are obtain- able from bars only j-inch in thickness, but an inci'ease of power is obtainable from several of such bars sepa- rately hardened and magnetized, and then laid together with their like poles in contact, or separated by thin brass. The compound bar thus foi'med, should be bound with a brass strap or band. The total force obtainable from such a compound bar, will not, how- ever, be equal to the sum of all their separate forces added together. For most of the experiments herein detailed, an ordinary bar magnet, 6 inches in length by l-incb in width and ^-inch in thickness, will suffice. A horse-shoe magnet of the same dimensions will serve for all purposes, and extend the range of the operations. A straight 6-inch magnet will cost one shilling, a 6- inch horse-shoe magnet with keeper, will cost two EXPEBIMENTS WITH MAGNETS. 7 shillings, whilst 6-inch compound horse-shoe magnets Fi;;. 3. A. Hoise-shoe Magnet. B. Keeper. Fig. 4. A Compound Horse-shoe Magnet. range in price from 6s. 8J. up to 15s., according to the number of bars in each. Fig. 5. Bar Magnets arraiigtd for Storage, with Wood between, and Keepers at the cud. § 4. Making Permanent Magnets. The first and 8 ELEGTRIGAL EXPERIMENTS. most important experiment to be performed with a per- manent magnet, is, to charge another bar of steel with magnetism. It has been shown in § 2, that a bar of steel may be charged with magnetism by stroking it with a natural lodestone. This magnetized bar may be employed in magnetizing other steel bars, and these in turn may be employed indefinitely for the same purpose, without limit as regards numbers, without weakening the charge in the originals. But, although the number of magnetized bars may be increased without limit by stroking them in turn with one permanent magnet, there is a limit to the strength of the magnetic charge obtain- able from a single magnet, and this limit is defined by the strength of the magnetic charge in the original inducing magnet. Hence we cannot induce a higher charge of magnetism in a steel bar, than exists in the inducing magnet employed in stroking the bar. A weak magnet may, howevei*, be made to induce a higher charge of magnetism than its own by the following device. Procure a number of very thin strips of hardened steel, and magnetize them one by one with the weak magnet. This done, bind the whole together to form a compound magnet, and with this magnetize the larger bar of steel, which can then be made to receive a charge equal in strength to that of the compound magnet. Every bar of steel varies in its capacity for receiving a charge of magnetism, with that of other bars of steel of equal size and weight, this variation beinf caused by the difference in their quality and temper. The quality of the steel very largely influences its capa- EXPERIMENTS WITH MAGNETS. 9 city for receiving a charge, but the temper or hardness of the steel influences its capacity still more. As a rule, a soft mildly-tempered steel is more readily magnetized than a hard steel, but the magnetic charge is not re- tained by the former. Every piece of steel has its limit of capacity,* which is termed its saturation point, beyond which it will not retain a magnetic charge. We may induce it to take a higher charge for the moment, but the charge will soon be dissipated until the point of saturation — that is, its highest capacity — has been reached. Every piece of steel also manifests a reluc- tance to receive a charge. Assuming that the magnetic charge is really an alteration in the arrangement of the molecules of iron and carbon in a steel bai", by which they are brought into a condition named polarization, then, it takes time, and a number of passes to efEect this alteration. If the steel is soft, its molecules are more readily altered than those of a bar of hard steel, the latter therefore manifests a higher magnetic reluc- tance. On the other hand, when the molecules have been altered and brought into a state of polarization, they will naturally manifest a reluctance to resume their former condition, their natural stiffness and un- yielding character favouring the retention of the charge. There are three methods by which a bar of steel may be magnetized: — 1. Contact by single touch. 2. Contact by double touch. 3. Magnetization by the inductive influence of electricity. § 5. Mag^netizing by Single Touch. Procure a bar of steel of any size up to 6 inches in length by f-inch 10 ELEOTRIGAL EXPERIMENTS. in width, by j-incli in thickness, and have it made as hard as fire and water will harden it — that is, let it be heated to a bright glowing red tint and dipped suddenly into very cold water. Place the hardened bar of steel on a table or bench, and stroke it with a permanent magnet in the following manner : — Lay the north pole end of the permanent magnet on the middle of the bar and draw the magnet slowly along to the end, then lift the magnet, lay its end again on the middle of the bar and again draw it to the end. This motion is shown by the direction of the arrow in Fig. 6. Eepeat this Fig. (3. Maguetiziug Steel liar by Single Touch. some ten or twelve times. Then reverse the ends of both steel bar and magnet, and magnetize the unmag- netized end in a similar manner with the south pole of the magnet. To make sure of the poles, mark this last end of the bar with a file, this should then be the north end of the newly made magnet. This done, test its strength on a few iron nails, and its polarity by its relation to another magnet, as shown in § 9. A horse- shoe magnet may be charged in a similar manner, taking EXPERIMENTS WITH MAGNETS. 11 care to have the north pole of the inducing magnet on the limb intended for the south pole of the other, as shown at Fig. 8 ; or a bar of steel may be magnetized ■with a horse-shoe magnet, as shown in Fig. 7. This Fig. 7. Magnetizing Steel Bar with Horse-shoe Maguet. c /»\s -JW J Fig. 8. Arrangement of Horse-shoe Magnets for Magnetizing and Preservation. method of magnetizing is only suitable to small magnets below the size given above, as it only produces a feeble magnetic power. It may be employed in magnetizing needles, steel pens, and other light pieces of steel used in experiments. If a piece of nnmagnetized steel is bent in the form of a horse-shoe magnet and placed with its two ends in contact with the poles of a per- manent horSe-shoe magnet on a plane surface, it may be strongly magnetized in the following manner : — Place a keeper made of soft iron on the bend of the nnmag- netized steel, across both limbs, and draw it along over the limbs of this and the magnet, to the bend of the magnet ; then lift the iron, place it again on the bend. 12 ELEGTEIGAL EXPERIMENTS. draw it along as before, and repeat this operation some twelve or fifteen times. Tarn over both hoi'se-slioes without separating them, and repeat the operation on the other sides. By this method, invented by Jacobi, the steel may ba powerfully magnetized, it is said, some fifteen to twenty jjer cent, higher than by the single- touch method first described. § G. Magnetizing by Double Touch. This method of magnetizing steel, invented by Dr. Knight in 1745, is also named magnetizing by separate touch. The bar to be magnetized, is laid on a plain sui'face such as that of a table or bench, and two opposite poles of two equally powei'ful magnets are placed on the middle of the bar, as shown at Pig. 9. The magnets are then l'"jg. U. Magneiziug Steel by Double Touch. drawn in opposite directions to the end of the bar, then lifted and placed again in the centre, as shown by the direction of the aiTows. This operation is repeated somo t-s*^elve or more times on one face, then the bar is turned over and the operation is repeated on the other face of the bar. This method was improved by M. Duhamel EXPEBIMENT8 WITH MAGNETS. 13 ■by placing the bai- on the ends of two fixed magnets, as shown at Fig. 10. Steel magnetized by this method is VT?^ S ft s Fig. 10. Duhamel's Method of Magnetizing Steel by Double Touch. found to be more permanently magnetic than by any of the other methods previously described. The bar to be magnetized forms a bridge across the two poles of two permanent magnets, and must be rubbed by another magnet with poles relatively arranged, as shown in the annexed figure. It should be noted that the relative positions of the poles must be maintained as shown in the figure, and the inducing magnets be inclined at an angle of from 15° to 20° to produce best results. § 7. Magnetizing by Electric Induction. If we en- velop a bar of unmagnetized hard steel with a coil of insulated copper wire, and send a strong current of electricity through the wire, the electric current will induce a magnetic charge in the steel, which will per- manently retain the charge after the current has ceased to flow. By repeating this operation several times, the steel will be charged up to its full capacity, and may then be said to be saturated with magnetism. Wire of U ELEGTBIGAL EXPERIMENTS. any size may be employed for this purpose, and it may be insulated with any of the insulating substances in general use for the purposes of insulation, but best results are obtained when the following conditions are fulfilled. The wire must be large enough to carry an appreciable volume of current without raising its tem- perature high enough to injure the insulation. As the strength of magnetism induced by such a coil is pro- portioned to the strength of the electric current flowing through it, the wire must be either large enough to carry a strong current, or must envelop the bar many times to multiply the effects of a weak current. The strength of the magnetic charge, is proportioned to the volume of electric current in amperes, multiplied by the number of turns in the coil. Hence, if a current of ten amperes is sent through one turn of wire wound around a steel bar, and a current of one ampere is sent through a wire making 10 turns around a steel bar, the magnetic strength induced in both will be the same. As the in- ductive influence of increased turns of wire becomes less when they are extended beyond three times the diameter of the core or central opening of the coil, it is advisable to have a thin insulation so as to have many turns of wire lying close to the bar to be magnetized. As No. 20 B.W.Gr. copper wire will carry safely 1 ampere of current, and No. 18 will carry 1'8 amperes of current, these sizes are to be recommended for magne- tizing coils. Silk soaked in melted paraffin is the best insulator, but cotton insulation costs less than silk, and may be employed where the least cost is a consideration. EXPEBniENTS WITH MAGNETS. 15 Although a magnet may be made by winding a quan- tity of insulated copper wire around a bar of steel, and sending an electric current through the coilj it is found more convenient, when making several magnets, to have a portable coil, in which the steel can be placed, magnetized, and withdrawn at will. To make such a coil, procure a strong reel or bobbin of wood having a body or core of a sufficient diameter to exceed the full size of the bars intended to be magnetized. Divide this reel into two equal parts by sawing the body in two obliquely, as shown at Fig. 11, then stick the two parts n. u — u Fig. 11. Split Bobbin for Goil of Wire. together temporarily with pitch or shoemaker's wax, and fill the reel with No. 20 silk-covered wire wound on regularly in coils side by side. Before winding on the wire, however, lay on two or four pieces of strong tape lengthwise along the body of the reel, and when the reel is full, tie these pieces of tape firmly to the coil. This will keep the coils of wire in form, after the two halves of the reel have been removed, and preserve the wire in the form of an open hank, as shown at Fig. 12. The hank should then be steeped in hot melted paraffin, and laid aside to cool. The coil of wire may be con- solidated with an alcoholic solution of shellac applied 16 ELECTRICAL EXPEIilMENTS. to each layer whilst winding on the wire, or with a solution of gum copal in ether, similarly applied ; or, if cheapness be desired, the reel or mandrel may be en- veloped in paper to prevent the wire sticking to it, and the layers of wire may be basted with hot glue. As a Fig. 12, Wire Coil for Magnetizing Steel, finish, the whole coil may be painted with sealing-wax varnish. To use this coil for the purpose of making permanent magnets, its two free ends must be connected to a powerful battery, such as two or three cells of a Grove or Bunsen battery arranged in series, or connected with some other generator of electricity having equal power. The bar to be magnetized is then placed in the coil, and moved backwards and forwards several times through the coil from end to end of the bai", at the same time i-apping it smartly with a rod of iron or any other metal. The vibration of the bar under these rappings tends to hasten magnetic saturation, and secure a higher mag- netic intensity. Frequent interruption of the current flowing through the coil has a similar effect, but the interruptions should take place when the bar is halfway into the coil, or, in other words, when the coil is near EXPERIMENTS WITH MAGNETS. 17 the middle of tlie bar, and this should be its position when the magnetizing process is finished. An electro-magnet may be employed in magnetizing steel bars, the process being the same as that of single or double touch with permanent magnets. Contact with the poles of a dynamo-electi'ic machine will also permanently magnetize steel, and even close proximity to such a highly magnetized field will induce a mag- netic charge in steel, — as the wearers of watches too often find to their cost. § 8. Lines of Magnetic Force. Although a bar of steel charged with magn^etism, has the charge equally distributed through every particle, or, in other words, is quite permeated with the charge, its manifestation is chiefly confined to the two ends. These are known as the two poles, and towards these the lines of mag- netic force are determined. This may be shown by placing a magnet under a sheet of smooth paper, or under a sheet of glass, and sprinkling some iron filings over its surface. On lightly tapping the paper or the glass with a quill or a straw, so as to slightly shake it and give movement to the iron filings, these will be arranged by the lines of magnetic force as shown at Fig. 13. If the paper be held over the poles of a horse-shoe magnet, the filings will be arranged as shown at Figs. 14 and 15. A close analogy is shown between the lines of a magnetic charge and that of a static charge of electricity, in the tendency to run towatds the terminal ends and leak ofE there, and also to induce an opposite charged condition named polarity at those c 18 ELEOTBIOAL EXPERIMENTS. terminals. This latter condition will be noted later on. The detrimental consequences of leakage from a magnet may be prevented by placing a piece of soft iron to each pole, or, in the case of a horse-shoe magnet, a piece of soft iron across the poles will suflBce. This piece of iron is named tlie keeper, because it keeps the magnetic Fig. 11. Lines of Moguetic Force — Horse-shoe Magnet. Fig. 13, Lines of Magnetic Force— Bar Magnet. charge from leaking off. The experiment with iron filings should be varied by using a bar magnet, a horse-shoe magnet, and two bar magnets parallel to each other with their opposite poles side by side, a,nd also with like and unlike poles end to end, as shown at Flo-. 16. The experiment should also be tried with, and without keepers to the magnets. If we wish to preserve EXPERIMENTS WITH MAGNETS. ■ 1 1 1 I M jl ^ssPSflBnSn HBbkwsa^^-^SS H B ^^ffljgj ^ql^s^bb^UHh ^^HP ^ ^ ^^ ^^^^ffl SSi ss ^^^ffl \nm[^^fffflBH B 1 1 1 ■ Fig. 15. Lines of Magnetic Force over the Poles of the Horse-shoe Magnet. RTTRACTIOM. REPULSION. Fig. 16, Lines of Magnetic Force around like and unlike Poles of 20 ELEOTBIOAL EXPEBIMBNTS. the arrangement of filings, the glass should have a thin coat of wax or of varnish. That the magnetic charge permeates the whole of the steel bar, may be proved by magnetizing a thin piece of very brittle steel, such as a hard-tempered piece of crinoline steel or a knitting needle, then breaking this into small pieces. Each piece will be found to be equally magnetized, and each will have polar extremities, as in the whole magnet. This is shown at Fig. 17. These fragments maybe used in further experiments to demonstrate the effects of heat I'ig. 17. Effects of Breaking a Magnet. on magnets. As the temperature is raised, the mag- netic charge will be dissipated, until, when at a red heat, no evidence of a chai-ge is perceivable, and the piece of steel will be'found to have lost it altogether. A simi- lar effect will follow from repeatedly jarring a magnet. § 9. Magnetic Repulsion. Although the natural attribute of a magnet is to attract, it also possesses the power of repulsion. Ifc has been shown in the preceding section, that a magnet is capable of attracting iron at both of its poles, as the iron filings cluster around both in equal quantity. Its behaviour to other EXPERIMENTS WITH MAGNETS. 21 magnets, is, however, quite different. The folio-wing law governs the actions of magnets to each other : — Poles of the same name repel j but poles of a contrary name attract one another. That is to say, the north pole of one magnet will repel the north pole of another magnet, but attract the south pole of the second magnet, and the south poles of the same magnets will repel each other. This may be shown in the following Fig. 18. Wooden Gallows. manner : — Either make a small gallows of wood, as shown at Fig. 18, or procure a piece of stout brass wire from 12 to 15 inches in length, bend one end to form a small hook, and a longer piece of the same end to form a larger hook or arm, and fix this in a piece of wood or a suitable stand. To the small hook hang a filament of unspun silk, or a piece of soft cotton, with a small stirrup of brass wire hung to a fibre of unspun silk 22 ELECTRICAL EXFEBIMENT8. attached to the lower end. A magnetized needle or a magnetized steel pen must be nicely balanced in this stirrup. If a filament of unspun or cocoon silk is employed, the needle will take up a position when at restj pointing due north and south. If we bring the north pole of another small magnet near the north pole of the suspended magnet, it will swing away as if repelled by a breath of air. If, however, we bring the Fig, 19. Stirrup to hold Magnets, Tubes, etc., in Electrical Experiments. north pole of the magnet in near proximity to the south pole of the suspended magnet, it will be attracted. If a large magnet is employed, the action will be strong, and may spoil the experiment by attracting the sus- pended magnet instead o£ repelling the opposite pole, and may also reverse the poles of the smaller magnet. It will be advisable to substitute an iron nail or a piece of iron wire for the magnets, and note the difference. Both< ends of the iron wire will be attracted equally to EXPERIMENTS WITH MAGNETS. 23 either pole of the magnet. If the iron wire is sus- pended in the stirrup, it will be attracted to the magnet J but if the magnet is in the stirrup, it will appear to be attracted to the iron. This will illustrate the influences of masses of iron such as that of an iron ship on the movements of the mariner's compass. If two bits of iron wire are suspended by two threads from the hook, they will mutually repel each other when a magnet is brought near them. Magnetic re- pulsion may also be illustrated by hanging a piece of iron, such as a key or nail, to one magnet, and then sliding the opposite pole of another magnet along over the first. When the pole of the second magnet is near enough to the suspended article, it will drop as if the magnetism of the first bar had been lost, but this is not so, the apparent loss being due to mutual repulsion. § 10. Mayer's Magnetic Floating Needles. This beautiful experiment (devised by Prof. A. M. Mayer, of the Stevens Institute, New Jersey), illustrates both magnetic repulsion and the reciprocal action of magnets. Procure a number of stout sewing needles, and an equal number of small corks, ^-inch in diameter by |^-inch in length. Magnetize all the needles, some with their eyes and some with their points north poles, and stick each in a piece of cork, with the eye of each needle just showing above each piece of cork, as shown at Fig. 20. Throw them all into a large bowl of water, and note their behaviour. Next get a bar magnet and pass one of its poles slowly over the floating magnets. If the north pole of the magnet is presented to them, all those with 24 ELEGTRIOAL EXPERIMENTS. eyes having a similar polarity will be repelledj whilsfc those with a south polarity will be attracted. The floating magnets will also repel or attract each other, and thus ai'rauge themselves in sets of geometrical figures, as shown in the annexed illustration. The floating magnets may then be sorted into two bowls of water, one containing north pole needles and the other ©■ ^ ^ O '^ o ^ G o o o ® O Fig. 20. Mayer'.s Magnetic Needles. I south pole needles, when the experiment with the bar magnet may be repeated. A bit of red sealing-wax on the north pole needles and a bit of blue sealino--wax on the south pole needles will serve to distinguish one from the other, and give additional interest to their movements. § 11. Magnetic Boats, Fishes, and Birds. A series EXPERIMENTS WITH MAGNETS. 25 of very pretty parlour experiments may be performed with a moderately strong horse-slioe permanent magnet and a few pieces of iron wire properly arranged in ways now to be described. 1. "With a sharp pocket-knife as a tool, carve out of cork, willow, alder, sycamore, or similar light wood, a fleet of tiny model boats, from f to 1 inch in length. Insert in each boat a keel of iron wire, and bring one end of the wire over the bow to form a cut-water. Paint each little boat or ship as fancy may direct, allow the paint to dry, then float the little fleet on a bowl of water. This fleet will follow a magnet held over it or near it, and, if a bar magnet is held in a stick fashioned as a magician's wand, the movements of the whole fleet inay be controlled by waving the wand over it or pointing to any part of it. If some larger models, shaped as ships and fitted with magnetized pieces of steel, be introduced into the fleet, a still further variety of movements may be effected, as the magnetic ships attract the boats or repel each other. 2. Models of swans, ducks, geese, and other aquatic fowl may also be made in wax, or carved out of wood, each being furnished with a small magnet, or with a piece of iron wire, or an iron brad. These flocks of aquatic models may be induced to follow a piece of bread or a biscuit in which a magnet has been con- cealed, whilst those furnished with small magnets may be made to scatter and scurry away by pointing a magnetized steel gun at them, providing the barrel of the gun be pointed near a like pole of the magnet concealed in the bird. 3. Another variation of the even- 26 ELEGTEIOAL EXPERIMENTS. ing's amusement may be provided by constructing a few small fisli out of very thin tinned iron, such as that used in making condensed milk tins, and throwing these in the bowl of water. If the small pieces of tin are cut out with scissors or shears in the form of two halves of a fish, then bevelled, and the two halves care- fully soldered together so as to make the fish hollow and water-tight, it will float, whilst others may be made not so buoyant, and others to lie on the bottom of the bowl. The models should be lacquered with suitable coloured lacquers, and, if they can be made of stamped pieces of tin to more nearly resemble fish, so much the better. These fish may be caught with a mag- netized hook, or be made to follow artificial bait con- cealing a magnet. 4. A pleasant variation of the same experiment may be performed with stuffed birds, or models of the same. Birds made of various tinted plush and feathers, attached to frameworks of iron wire, and mounted on oscillating perches in various parts of the room, or suspended with [outstretched wings from pendants or brackets, may be animated with a magnetic wand and induced to peck at biscuits concealing magnets. If ordinary stuffed birds are to be utilised in this experiment, a small piece of iron should be concealed in each head or beak, and each bird so poised as to fall back in a position of rest when the magnet has been withdrawn. This may be done by placing a small piece of lead under the tail of each bird. Insects such as bees, butterflies, and dragon- flies, may be made of plush and rice-paper artistically EXPERIMENTS WITH MAGNETS. £7 painted^ and suspended by cocoon silk from stalks of ferns or flowers, and ttese may be agitated by passing the magnetic wand over tbem, if each insect contains a piece of iron wire, or has a framework of this wire. With a strong short bar magnet concealed beneath the fore-finger of the right hand, a semblance of magic may be imported into the entertainment. Magic Wand. To construct a magic wand for use in these experiments, get an ebony ruler or one of ebonized wood (any other wood, or ivory, will serve the purpose), bore a hole through it, or bore a hole in each end, and either insert a long thin rod of magnetized steel, or two short bar magnets, one in each end, with a south pole at one end and a north polo at the other. These may be so arranged as to be removable at will, if desired, by unscrewing the capped end of the ruler. Otherwise, the ends of the magnets may be disguised with black enamel or black sealing-wax. The wand may have ornamental ends, and be carved or turned, or orna- mented as taste may direct. § 12. Magnetic Suspension. To some persons im- perfectly acquainted with magnets, it may seem pos- sible to so arrange a magnet and a piece of iron and steel as to keep the latter suspended in the air, at a fixed distance from the magnet. As, however, one of the laws of magnetism, discovered by Coulomb, is that magnetic attractions and repulsions vary inversely in strength as the squares of the distances from their poles, it follows that any attractive material brought within the attractive influence of the magnet must be drawn to 23 ELECTBIGAL EXPERIMENTS. it, since when once within the sphere of attraction the strength of this rapidly increases. Magnetic suspen- sion in mid-air can only be effected by holding the attracted object back from actual contact with the magnet by means of a filament of silk or similar fibre, or by nicely balancing the iron or steel between the attractions of two magnets. Magnetic repulsion may be illustrated by means of an experiment with a magnetized needle held over a magnet by a thread of cocoon silk. If the point of the needle is given a north polarity and held over the north pole of a strong magnet, the needle will be repelled upward and appear to be, floating in the air over the magnet. This ex- periment has been named " Mahomet's coffin," to com- memorate the erroneous notion, once entertained, of Mahomet's body being placed in a steel coffin and sus- pended in the air between two magnets in a mosque at Medina. By attaching a thread of silk by means of wax to the underside of an iron bar and holding a strong magnet over it, the iron may be made to appear as if suspended in air by magnetic attraction. Another interesting experiment, illustrative of mag- netic suspension, may be performed with a pendulum furnished with an iron top nicely rounded on its upper end. This rounded part must be placed in contact with a strong bar magnet, from which the pendulum may be suspended by magnetic attraction, and can then be swung to and fro or made to describe a circle without loosening its hold, providing the weight is proportioned to the strength of the magnet. EXPERIMENTS WITH ilAGNETS. 29 When iron is in contact with a permanent magnet, its strength or power of holding up a weight is increased. This is named the portative force of a magnet. It may be tested by attaching a scale-pan to the iron keeper, and adding weights or lead shot until the keeper parts from the magnet. The magnet must be suspended vertically, and the scale-pan must be hung from a point exactly in the centre of the magnet or midway between the two poles. Magnets have been made to sustain ten or twelve times their own weight, and Jamin con- structed compound magnets of thin steel plates which sustained fifteen times their own weight. These com- pound magnets were constructed with five or six thin horse-shoe magnets bound together with a brass band, this ai'rangement making a stronger magnet than a solid bar of steel the same thickness. He found, how- ever, that the strength of these magnetic batteries was not proportioned to the number of thin magnets thus bound together. For instance, taking a thin magnet capable of holding up a three-pound weight, — by bind- ing six such magnets together he could not get the compound magnet to hold up six times three poundsj but only fifteen pounds, the power to hold the remain- ing three pounds being lost in the repellent action of one magnet on another. The strongest compound mag- nets are those whicb are made of five or seven thin horse-shoe magnets of unequal length, bound together with one long magnet in the centre, the next two on each side being ^-inch shorter, the next shorter still, and so on. By this arrangement the repellent 30 ELECTRICAL EXPERIMENTS. action of like contiguous poles on each other is much reduced. § 13. Magnetic Induction. That a magnet has the property of inducing magnetism in a piece of steely has been clearly shown in § § 2 to 6. It also has the property of inducing a magnetic charge in a piece of iron, and converting this into a magnet whilst within the sphere of magnetic influence. An interesting experiment illustrating this property, may be performed with a number of thin iron bars, such as sti'ips of hoop- iron, and a moderately strong horse- shoe magnet. Sus- pend the magnet with its 'poles in a vertical position, and attach one end of the first strip to one pole of the magnet. It will be seen that the iron has become a magnet by induction, for it will attract another strip of iron held to its lower end. Add another strip of iron, this also will be attracted to the first strip by magnetic induction. Add strip to strip in a similar manner, as long as that pole of the magnet will bear the weight, then add similar strips to the other pole. It will be found that a magnet can hold up a greater weight of such strips arranged in this way than it can of similar strips placed across the poles, because each strip induces magnetism in its neighbour, thus affording mutual support, and the magnetic influence is extended to a greater distance from the poles. If long intervals of time are allowed to intervene between each addition of weight in both cases, the portative strength of the magnet itself will be increased. The experiment may be varied by adding ^-inch lengths of f-inch iron rod to EXPERIMENTS WITH MAGNETS. 31 each other until a string of such pieces has been formedj all held together by the attraction of magnetic induction. A neat little experiment, illustrating magnetic induc- tion, is described in Mr. Perren Maycock's " First Book of Electricity and Magnetism,"* and is shown in Fig. 21. A permanent bar magnet is bound to a strip of iron of Fig. 21. Bar Magnet attracting Iron Filings b; Inductive Influence on an Iron Bar. equal size, with a strip of wood between the two bars. When thus arranged, the two metals do not touch each other, but the inductive influence of the magnet is transmitted through the intervening strip of wood to the iron, and this becomes magnetic. This is proved by sprinkling some filings on a sheet of paper, and presenting the iron only to the filings, when they will be attracted as shown in the figure. Magnetic induction is also capable of being trans- * Published by Whittaker & Co. Prices 2s. 6d. 32 ELEG'flilGAL EXPERIMENTS. mitted to a long distance througli wires. This is shown in the magneto call bells, employed in telegraph and telephone system Sj and the magneto machines used in working the ABC telegraph instruments. Its action on a small scale may be demonstrated by a simple experiment made with a bar magnet and the mag- netizing coil described in § 7. Connect the two ends of the coil to a delicate galvanometer, and plunge the magnet in the coil. At the instant of doing this, the needle of the galvanometer will be deflected, and it will be again deflected when the magnet is removed from the coil, thus showing that the magnetic impulses are taken up by the coil of wire, and the charge is trans- mitted to the coil of the galvanometer, where it induces a magnetic action on the needle. In the machines for ringing magneto call bells, and for working ABC telegraphs, permanent magnets are swiftly revolved near coils of wire, and the rapid succession of magnetic impulses are transmitted from these coils to similar coils wound over iron cores in the distant instruments. This inductive action of permanent magnets, estab- lishes the relation of magnetism to electricity, the action of both being reciprocal ; for, as a cui'reut of electricity passing through a coil of wire wound over a steel bar induces a magnetic charge in the bar, so, a magnet moving in a coil of wire sets up a current of electricity in the wire. § It. Miscellaneous Magnetic Experiments. Give a boy a horse-shoe magnet and a miscellaneous col- lection of metal scraps, together with clear instructions EXPERIMENTS T\^ITH MAGNETS. 33 in the use of the magnet, and he will amuse himself by the hour. The following may be suggested among many others as most likely to engage his attention. Assorting Metal. Put into a box, or a tray, a number of brass buttons, white metal buttons, and iron buttons, all l^quered or japanned to disguise them. Also, some iron, brass, copper, and other metal brads, tacks, and nails, japanned, lacquered, painted, or tinned, to give them a uniform appearance. These should be assorted by the aid of a magnet. The magnet will pick •out all the iron buttons, brads, and nails. Common tinned iron pius may be thus detected when mixed with tinned brass pins. Jack Straius. Get some iron wire of about No. 16 gauge, cut it into various lengths of from 3 to 6 inches, and paint the pieces in various colours and tints, or furnish each with a head of coloured glass or wood. Give to each a number or value, mix them altogether in a tray or box, and proceed to pick them out as in the game of Jack Straws, using a magnet for the purpose. A few blanks of brass or of copper wire introduced among the iron wires will serve to increase the interest of the game. The game may be varied by placing a number of iron wires of various lengths in an envelope, with their ends only protrud- ing, and drawing them one by one from the envelope with the magnet, as in '• drawing Jots." Wire nails of various lengths may be substituted for lengths of iron wire. Magnetic Screens. A magnet will exert its influence D 34 ELECTBIGAL EXPEIilMENTS. on iron and steel througli nearly all known substances except iron itself. Get a pocket compass, or the small galvanometer described by Mr. Bottone in " Electrical Instrument Making for Amateurs/' and sold for 2s. 6t/. Place tliis on a table, on a mantelpiece, on a mat or rug, on a slab of glass, slate, marble, porcelajn, or similar stony substance, or over any other metal except iron, then place a strong magnet under the substance interposing between it and the compass. If the sub- stance be not too thick, the needle of the compass will be influenced by the magnet in a most interesting manner. A piece of sheet iron will screen the com- pass from magnetic influence and alter its behaviour altogether. § 15. Uses of Permanent Magnets. Permanent magnets have been and are employed in the construction of magneto-electric machines, as indicated in the last section, and described by Mr. Bottone on pp. 15 and 175 of his book "Electi-ic Bells, and All About Them," and also in Mr. Poole's " Practical Telephone Handbook," pp. 94-102. They are also employed in the construction of magneto-electric shocking machines, as described by Mr. Bottone in his book " Electric Instrument Making," pp. 90-99. The telephone owes its oi'igin to a dis- covery of the effects of magnetic induction on a diaphragm of thin iron. Permanent bar magnets are employed in the construction of Bell telephone re- ceivers, whilst horse-shoe permanent magnets are used in the Gower, Ader, Siemens, and some other telephone receivers. The single-needle telegraph instrument, EXPERIMENTS WITH MAGNETS. 35 which has rendered such good service to all the world as a means of intercomtnnnication between the nations, depends upon the action of a small magnet for its efficiency. This action may be thus explained. Where a small magnetized bar of steel is suspended or pivoted in a vertical position in a coil of fine wire, and a current of electricity is sent through the coil, its hollow core is magnetized, and the magnetized air space be- haves toward the magnetized needle much the same as a permanent magnet, repelling like poles and attracting unlike poles of the magnetized steel. The magnetized steel, being free to move in this space, is attracted or repelled according to the polarity of the air space, this being controlled by the direction of the electric current passing through the coil. When the current is made to flow from left to right in the coil, its air core has a north polarity at the right-hand end and a south polar- ity at the other end. As a consequence, the north pole of the vertical steel magnet is repelled from the right- hand end of the coil, and the south pole is attracted to that end. By reversing the direction of the current, the polarity of the coil is reversed, and the magnetized needle made to swing in the opposite direction. The electric current detectors employed by telegraph lines- men and by electric bell-hangers are similarly con- structed. The galvanometers, voltmeters, and ammeters described by Mr. Bottone in his book " Electrical Instru- ment Making for Amateurs " are constructed on similar principles, adapted to a magnetic needle poised hori- zontally over a coil of wire. Experiments, illustrating 36 ELEOTBICAL EXPEIilMENTS. these principles, will be given when considering the effects of electro-magnetic inducbion. Permanent mag- nets are also employed in electric indicators, measuring instruments, and other electric instruments. Although these uses of the permanent magnet are of great importance to the civilised world, they may be said to occupy an inferior position to the use of it as a guide to the mariner conducting the commerce of nations across the trackless expanse of ocean which (Y Fig. 22. Magnetized Needle balanced on a pointed Steel Pivot. separates the continents and countries of the earth. We have already noted in § 9, that when a mag- netized steel needle is suspended in mid-air by a filament, and free to move in any direction, it takes up a position pointing due north and south. This action of the magnetized needle is brought about by the influence of the earth's magnetism, exercising a directive force on the needle under the well-known law of like poles repelling and unlike poles attracting each other. EXPERIMENTS WITH MAGNETS. 37 The earth itself is a large magnet, exerting its influence on all magnetized and magnetizable substances. The poles of this magnet are situated near the axis of its diurnal revolution. When therefore a magnetized bar is suspended above the earth's surface, one end is attracted to one of the earth's poles, and the other end to the opposite pole. The same effect follows if the needle be nicely balanced horizontally on an almost f rictionless pivot, .as shown at Fig. 22. This is done in Fig. 23. Section ot Compass Box. A. Compass Card. B.B. Gimbals. C. Glass Cover. N. Needle. P. Pivot. the construction of the mariner's compass. A mag- netized needle has a hole in its centre, bushed with an agate cap, having a conical interior, and this is nicely poised on a steel point, as shown- in Fig. 23. A card or a disc of mica (A), having a diameter a little larger than the length of the needle (N), and lettered with letters indicating the various points of the horizon, is either fixed to the upper surface of the needle, with its north-seeking pole under N. of the card, and its south-seeking pole under S., or under the needle, with this free to move about it as in a small pocket compass. The whole is enclosed in a brass box, 38 ELECTBtCAL EXPERIMENTS. Fig. 24. Portable Boat Compass. Fig. 25. The I>ipping Needle. EXPERIMENTS WITH MAGNETS. 39 as shown in section at Fig. 23, supported on gimbals to keep the compass in a horizontal position when the ship is in motion. The compass is placed in a box named the binnacle near the ship's stern and near to the steersman, who can then see, by the relative position of the ship to the points on the compass card, the direction of the ship's coui-se. Another use of the magnetic needle is shown in Fig. 25, which illustrates the position taken by a magnet free to move vertically, as well as horizontally. The dip and angle of the needle shows the intensity of the earth's magnetism. This varies at different points on the earth's surface, and is shown on the figure as 67° for London. This arrangement is named a " dipping needle." CHAPTER II. EXPERIMENTS WITH ELECTRO-MAGNETS. § 16. Relation of Magnetism to Electricity. In the preceding sections of tliis book, we have been able to show some of the relations which exist between mag- netism and electricity. In this chapter, we shall show by means of simple experiments, a still closer relation between the two forces. To perform these, we shall require a generator of electricity such as a dynamo, or a primary battery, capable of giving an electric current having a volume of at least one ampere through a resistance of 10 ohms. This current will be furnished by 5 or 6 cells of the Bunsen, Grove, Bichromate, or Chromic Acid types, or 10 cells of the Daniell type, or one of the hand-power dynamos built to light a 5 c.p. incandescent lamp. A generator of less power will serve our purpose for some of the experiments, but all will derive additional interest from using a powerful current. 1. The Magnetic Shell. Every conductor of electricity is surrounded with a magnetic influence enclosing it as in a shell. An experiment to prove this may be per- formed with one or two cells of a battery. Get a sheet of notepaper, or any other smooth paper, and support EXPERIMENTS WITH ELEOTROMAQNETS. 41 it on a frame or ring of wood by glueing, pasting, or gumming it thereto, then pass a piece of copper or brass wire (No. 20 gauge) through the centre vertically, and secure the ends of the wire to two metal clips Fig. 2C. Magnetic Shell around an Electric Conductor. above and below the paper. Connect these clips in circuit with the electric generator or battery, sprinkle a few very fine iron filings on the paper, and gently rap it with a quill, penholder, or pencil. As the paper is thus made to vibrate under repeated slight raps, the Fig. 27. Magnetized Filings around a Wire. Fig. 28. Magnetized Filings over a Wire. filino-s will arransre themselves around the wire as around a magnet, thus showing that a magnetic influ- ence pervades the air, and surrounds the wire as a shell. By the exercise of care, the filings will show 42 ELEGTBIOAL EXPERIMENTS. the exact form and thickness of this shell, as at Figs. 27 and 30. Fig. 29. Horizontal Galvanometer. This experiment may be varied by stretching the conducting wire horizontally beneath the paper, as shown at Fig. 28, and arranging it to form various 9/tmKY Fig. 30. Shell of Iron Filings around the Line Wire of a Powerful Electric Battery. figures, all of which will be shown on the paper above, as the filings arrange themselves over the wire. The EXPEBIMENTS WITH ELEGTBO-MAGNETS. 43 wire may be bare, or may be coated with an insulating substance, without interfering with the experiment. The magnetic shell surrounding an electric conductor is also shown by reference to Fig. 30, which illustrates how iron filings will adhere to the line wire of a powerful battery. If the line wire of such a battery is carried down through a supporting platform of thin wood or of stout cardboard, we may test the extent of the sphere of magnetic influence by means of a small pocket N rt ' * © y > Wirt / {,\ Cun-tnV /V ^\ Cu-r-r-ml y „ ^^Ccmmf up. /^ ^^Qoiny dourn,'' Fig. 31, Testing the Sphere of Magnetic Influence around Electric Conductors. compass or a delicate horizontal galvanometer, when the results will be as shown at Fig. 31. On referring to this, it will be seen that the polarity of the current differs in the down line from that of the up line, and the compass needle varies its position as we move the compass. 2. Medro-Magnetie Induction. Procure or mate a delicate horizontal galvanometer such as that described by Mr. Bottone in his book "Electrical Instrument Making for Amateurs" (Fig. 29). Also procure a few U ELECTRICAL EXPERIMENTS. yards of No. 22 or No. 24 gauge copper wire, and form two model telegraph lines running parallel to eaoh other closely, side by side without actually touching. Connect the two ends of one line wire to the galvanometer, and the two ends of the other line wire to the battery. Im- mediately, on connecting one line with the battery, the galvanometer needle will be seen to move, and it will move again at the instant when the wire is disconnected from the battery, although the line in connection with the Fig. 32. Oersted's Induction Apparatus. galvanometer does not touch the line connected to the battery. This effect is produced by the magnetic shell or halo surrounding the battery line inducing a similar condition in the neighbouring wire, much the same as a permanent magnet induces magnetism in iron or steel in close proximity to it. Disconnect the galvanometer from the separate line and hold it close under the battery line, or better still (to prevent vibration of the needle by tremors of the hand) fix it in this position with the needle as close as it can be got to the wire, and let the needle lie in line EXPERIMENTS IVITH ELECTRO-MAQNETS. 45 with the ■wire when at rest. To do this the line wire must be moved in line with the magnetic meridian of the earth. On connecting the line with the battery, a movement will be observed in the needle/ which will deviate to right or left of the line according to the direction of the electric current passing through the wire. A pocket compass will serve this purpose as well as a galvanometer, or an apparatus to show this ex- pei'iment (shown at Fig. 32) maybe purchased at prices varying from 3s. 6d. to 10s. 6d. As like poles repel those of their own character, it naturally follows that one pole of the magnetic shell surrounding the wire must repel one end of the magnetic needle and cause it to swerve aside from its usual position of rest. This magnetic property of the electric current, discovered by Oersted, has been made use of in the construction of galvanometers and of telegraph instruments. 3. Electro-Magnetic Attraction, and Repulsion, It has been shown in § 9 that the like poles of permanent magnets repel each other, whilst unlike poles have the property of mutual attraction. Herein was shown the law of a magnetic circuit, the polarized molecules of matter tending to form a perfect endless chain. Pre- cisely the same law governs an electric circuit. The polarized molecules of two electric conductoi-s placed side by side, attract each other when both are moving in the same direction, but repel one another when moving in opposite directions. This law, discovered byM. Ampere, may be illustrated by means of an apparatus so de- vised as to have one electric conductor fixed and the 46 ELEOTBIOAL EXPERIMENTS. other freely movable. Such an, apparatus is shown at Fig. 33j named "Ampere's Stand and Rectangle/' costing from 30s. to 50«., according to finish. It con- sists of a polished mahogany stand, on which is fixed, at one end, a brass pillar carrying a projecting arm on top, terminating in a mercury cup ; at the opposite end of the stand another brass pillar is fitted, with a brass clip arranged for adjustment to any height, and made Fig. 33. Ampere's Stand and Eectangle. to hold a flat coil of fine insulated wire named a "multiplier," the foot of the pillar being fixed to a sliding plate working in grooves, for easy adjustment to any distance; between these two pillars a shorter hollow brass pillar is fixed, in which a brass piston slides up or down, as required, and bears on tho top a mercury cup. A long piece of copper wire is bent to form a double rectangular figure, as shown in the sketch, with its lower sides resting on a light strip of EXPERIMENTS WITH ELTSOTBO-MAQNETS. 47 wood, and one end of the wire passing througli the centre of the wooden strip to the mercury cup beneath, where it is counecbed to a suitable pivot point. The upper end of this wire also ends in a steel needle point, which pierces a small hole in the bottom of the upper mercury cup, and makes contact with the mercury. The whole is nicely balanced by copper balls under the wooden strip, and is free to move in a circle with very little friction, whilst the double rectangle of wire is also electrically connected with the upper and lower mercury cups. To work this apparatus we shall require a strong current from a Grove, Bunsen, or Bichromate battery of 4 cells arranged in series. Connect one pole of the battery to the long brass pillar, and the other pole to one of the binding screws on the multiplier, then con- nect the other screw of the multiplier by means of a piece of wire with the foot of the stout pillar. If the positive pole of the battery be connected to the foot of the long pillar, the current will traverse the right limb of the rectangle in a downward direction, and will also traverse the multiplying coil in the same direction, if the battery has been rightly connected. The effect of this uniform direction of current in both multiplier and wire will be to draw the right-hand limb of the rectangle toward the coil, when both are brought near enough by moving the clip and pillar supporting the coil. If the current is now sent in the reverse direction through the coil, the wire will be repelled. A series of very interesting experiments with similar 48 ELECTRICAL EXPERIMENTS. apparatus is given in " Ganot's Physics," chapter iv., §§ 846-861, under the head of " Attraction and Repul- sion of Currents by Currents." 4. Biamagnetic Experiments. The magnetic influence of a powerful electro-magnet extends beyond the immediate neighbourhood of its poles, and induces a temporary magnetic condition in other substances besides those of iron and steel. Coulomb discovered in 1802 that all bodies are more or less affected by magnetic influences. Faraday discovered in 1845 that a powerful electro-magnet had a peculiar influence on all bodies, solid and liquid, brought by him within the magnetic field, — that is, the space just in front of and between the polar extremities of the magnet. Some of these bodies were repelled and some were attracted by the magnet. These bodies were arranged by him in two classes. Those that were attracted to the magnet he named paramagnetic substances, whilst those that were repelled he named diamagnetic bodies. Para- magnetic bodies are attracted to the electro-magnet, and point axially like a suspended magnetic needle. Dia- magnetic bodies are repelled, and point equatorially, that is across the axis of the magnet's bobbins. The following substances have been experimented upon, and arranged in their several classes : — Paramagnetic Bodies. Iron, nickel, cobalt, manganese, chromium, cerium, titanium, palladium, platinum, osmium, paper, sealing-wax, fluor spar, peroxide of lead, plumbago, China ink, Berlin porcelain, red lead, sul- phate of zinc, shellac, silkworm gut, asbestos, vermilion. EXPERIMENTS WITH ELECTRO-MAGNETS. 49 tourmaline, charcoalj basic salts of iron, oxide of tita- nium, oxide of chromium, cliromic acid, salts of man- ganese, salts of chromium, oxygen. Diamagnetic Bodies. Bismuth, antimony, zinc, tin, cadmium, sodium, mercury, lead, silver, copper, gold, arsenic, uranium, rhodium, iridium, tungsten, rock crystal, mineral acids, alum, glass, litharge, common salt, nitre, phosphorus, sulphur, resin, spermaceti, Iceland spar, tartaric acid, citric acid, water, alcohol, ether, starch, gum arable, wood, ivory, dried matter, Fig. 34. Diamagnetic Experiment with Copper Cube. fresh beef, dried beef, apple, bread, leather, fresh and also dried blood, caoutchouc, jet, turpentine, olive oil, hydrogen, carbonic acid, nitrous acid, nitric oxide, defiant gas, coal gas. Nitrogen is neutral to magnetic influence. Powders, gases, and liquids are examined in thin and slender glass tubes suspended in a fibre stirrup by a thread of cocoon silk between the poles of the electro- magnet. Powders and liquids may also be examined on a watch-glass placed on flattened soft iron extensions screwed into tapped holes in the ends of the magnet cores. Conical and other forms of terminals to suit the E 50 ELEOTBIGAL EXPERIMENTS. experiments are attached to the ]poles as required^ in a similar manner. When liquids are being examined in watch-glassesj a diamagnetic liquid is known by its behaviour in retreating from the poles and forming a little heap, whilst a paramagnetic liquid is attracted Fig. 35. Diamagnetic Experiment with Candleg toward the poles, and becomes flattened or of concave form. Solids should be formed into cubes where' practicable, and suspended by silken threads between the poles, as shown at Fig. 34. Flames and smoke may be examined by holding the flaming or smoking sub- stance between the poles, as shown at Fig. 35. The behaviour of flames will be found very interesting, being Ri^i uiium WidL IlMiA Fig. 3C. Paramagnetic Fluid. Fig. 37. Diamagnetic Fluid. elongated, flattened, or depressed according to their position. Candle and taper flames are repelled. A record of experiments in diamagnetism will be found in " Ganot's Physics," and in " Pepper's Playbook of Science." EXPERIMENTS WITH ELEOTBO-MAGNETS. 5i § '17. Simple Electro-Magnets. The intimate re- lation between magnetism and electricity is most clearly shown by the inductive influence of the latter on soft iron, converting it into a magnet whilst under electric influence. If we take a rod of soft iron and wind over it several turns of insulated copper wire, we may convert the iron into a magnet at will by sending a strong current of electricity through the wire coil wound over the iron. A simple electro-magnet may be con- structed out of an ordinary French wire nail and a yard or so of No. 24 silk-covered copper wire. Wind the wire in regular turns side by side around the nail, and in regular layers, until only a length of some 4 or 5 inches has been left at the commencing and finish ends. Connect these ends to the battery, and note the mag- netic condition of the nail by hanging iron brads to its head as to the pole of a permanent magnet. If the wire is wound around a 3-inch length of |-in. iron rod, and about a foot or so of wire is left at each end for connection with the battery, a number of interesting magnetic experiments may be performed (as with a permanent bar magnet) whilst the wire coil is connected with the battery and a current of electricity is passing through the coil. In fact, all the experiments perform- able with a permanent bar magnet may also be per- formed with this simple electro-magnet. In addition to these, we may illustrate the fact that the iron is only magnetic whilst a current of electricity is passing through the coil. Small iron articles picked up with this magnet will be dropped instantly when the electric circuit is 52 ELEGTBIGAL EXPERIMENTS: broken, as when the wire is disconnected from the battery. By the exercise of a little ingenuity and skill, a magic wand may be constructed, with an electro- magnet at one end and a spring switch at the other, connection being made with the battery by means of a flexible conducting cord carrying two wires. The cir- cuit can be completed and the electro-magnet put in action by pressing a spring in the handle. Magnetized Steel Filings. A very interesting experi- ment can be performed by substituting a glass tube filled with steel filings for the iron rod last used. Get a glass tube, stop one end with a cork, fill the tube with steel filings, then stop the other end with a cork. Wind the insulated wire around this tube, instead of the iron rod, and send a strong current through the coil. The steel filings will then exhibit all the properties of a permanent steel magnet, even after the circuit has been broken and the tube removed from the coil, if this is done carefully so as to leave the filings undisturbed. If, however, we shake the tube, all the magnetic pro- perties of the filings at once disappear, because then north and south poles of the particles become jumbled indiscriminately together, and these neutralise each other. This experiment has been employed by science teachers to show the bad effects of jolting and knocking per- manent magnets. § 18. Horse-shoe Electro-Magnets. If a length of soft iron is bent into the form of a horse-shoo and covered with insulated copper wire, as shown in Fig, 38, it will be converted into a powerful electro-magnet when a EXPERIMENTS WITH ELECTRO-MAGNETS. 53 strong current of electricity is sent through the coil. The usual method of coiling the wire on a horse-shoe electro-magnet is as shown in Fig. 40, — that is to say, part of the wire is wound on one limb from left to right, and the rest of the wire is wound on the other limb in the opposite direction. This insures north polarity in the magnetism of one limb and south polarity in the opposite limb, and, as opposite poles attract each other, the magnetic strength of the poles is much increased Fig. 38. Simple Bar and Horse-shoe Electro-Magnets. by this arrangement. The polarity of either limb is determined by the direction of the electric current pass- ing through the coil of wire wound over the limb. For instance, taking Fig. 38 as an illustration, if the current enters at S and leaves at N, S will be the south pole and N the north pole ; but if the cuiTont enters at N and leaves at S, then N will be the south pole and S the north pole of the electro-magnet. The north pole is always to the left of the current when flowing in a coil of wire wound over an iron rod. This has been gra- C4 ELECTRICAL EXPERIMENTS. phically represented by imagining a boy lying on bis stomacb over a roller and trying to move forward. His forward movement represents tbe movement of tbe current, and bis left band tben points to tbe nortb pole of the roller. If he turns round and rolls in tbe opposite direction, tbe poles are reversed. The polarity of an electro-magnet may also be determined by bringing a pocket compass or a suspended magnetic needle near tbe poles, when tbe nortb pole of tbe needle will be repelled by tbe north pole of the magnet, whilst its Figs. 39, 4.0, 41. Varietiog in forma of Electro-Magnets. south pole will attract tbe nortb pole of the needle. Suspend two magnetized needles with like poles in front of a horse-shoe electro-magnet, and note the behaviour of tbe two needles. One limb of the magnet will attract one needle and the other pole repel tbe other needle. Any of tbe experiments performable with a per- manent horse-shoe magnet may also be performed with a horse-shoe electi'O-magnet, and similar experiments may be performed with it as with a straight bar electro- magnet, In addition to these, some interesting experi- EXPEBIMENT8 WITH ELEOTBO-MAQNETS. 55 ments may be performed in lifting heavy weights attached to its armature, attracting the armature through space, and noting the distance under several variations of current strength. Variations may also be made in the shape and size of the magnets, and in the disposition of the wire coils wound over the limbs. It is not neces- sary to have an iron rod bent into horse-shoe form for double-pole electro-magnets. The two cores or limbs may be screwed into or rivetted in a heavy yoke of soft iron with the best results, — in fact, this is the general form given to it in all electric instruments in which it is employed, as in electric bells, etc. § 19. Electro-Magnetic Portation. This term is used to indicate the carrying power of an electro-magnet, — that is, its ability to pick up and carry by its power of attraction a weight attached to its armature. The poi-- tative power of an electro-magnet is limited by : — 1. The saturation limit of magnetism its cores are capable of receiving. 2. The number of turns of wire wound over the cores., 3. The capacity of the wire for carry- ing currents. 4. The strength of the current passing through the wire coils wound over its cores. Respecting these conditions we may note that: — 1. The saturation limit of magnetism in pure soft iron is 200 lbs. per square inch. Ordinary commercial iron has a saturation limit forty per cent, below this, but increased strength of curfent flowing through the coils will cause iron to assume a higher limit. 2. The porta- tive force of the electro-magnet is increased by an increased number of wire convolutions wound over its 56 ELEOTSICAL EXPEEJMENTS. coresj providing the thickness of these do not exceed three times the diameter of the cores, nor extend beyond four times the diameter of the cores, fi-om their polar extremities. Short dampy electro-magnets are stronger than long thin ones of equal weight. 3. As the porta- tive force of an electro-magnet depends upon the strength of the current passing through its coils, mul- tiplied by the number of coils themselves, it follows that the wire must have sufficient capacity to carry the current necessary to obtain complete saturation of the iron. The capacity of any given gauge of copper wire may be found by consulting the wire table published in " Induction Coils." ' 4. The magnetic force developed in the core of an electro-magnet is governed by the number of ampferes of current passing through its coils, multiplied by the number of wire convolutions. The magnetism set up in an iron core is, up to the saturation point, equal to the number of ampere turns coiled around it. In good soft iron it takes 5,000 amperes of electric current to saturate 1 cubic inch of iron with magnetism. If we can force 1 ampSre of current through a coil of wire wound around an ii'on core 5,000 times, within the limits already prescribed, the core will be saturated with magnetism, since each turn carrying 1 ampfere of cur- rent increases the portative force of the magnetized core. The same result is obtained from 2 ampSres of current through 2,500 turns, or 5 amperes of current through 1,000 turns of wire. ' " Induction Coils," by G. E. Bonner, price 3s., published by Whittaker & Co. EXPERIMENTS WITH ELEGTE0-MAQNET8. 57 Experiments with horse-shoe electro-magnets wound with various lengths and gauges of wire, may be tried, and their portative force ascertained by means of a Fig. 42. Electro- Magnet with Wire heaped on the Poles. balance scale attached to their armatures and gradually weighted. Care must be taken not to greatly exceed the limit of the carrying capacity of the wire, or its insulation will be destroyed. When it is necessary to wind more than one layer of wire on a horse-shoe magnet, the wire is first wound on two bobbins and Fig. 43. Powerful Electro- Magnet on a Stand. these slipped on the poles of the bent iron, or the wire may be heaped over the poles of the magnet, as shown at Fig. 42. When the portative value of an electro- 58 ELEGTBIGAL EXPEBIMENTS., magnet is to be ascertainecl, it will be. found convenient to suspend it to a small tripod, as shown at Fig. 44. For diamagnetic experiments, the magnet is fixed to a stand, as shown at Fig. 43. Fig. 44.. Tripod for suspending Magnets. § 20. Electro-Magnetic Solenoids. It has been shown in previous sections, that a wire conducting a current of electricity is surrounded by a shell of mag- netized air. It has also been shown that iron and steel enveloped in wire carrying an electric current, both become magnetized. It has also been shown that a steel bar may be permanently magnetized by placing it in a coil of wire through which an electric current is passing. Such a coil of wii'e, when not occupied by a core of iron or other metal, contains a core of air, and this core becomes itself an electro-magnet, with poles similar in every respect to those of an iron core when a current of electricity is sent through the coil. A hol- low coil of wire, such as that shown at Fig. 12, § 7, EXPEEIMENTS WITH ELEGTB0-MAGNET8. 59 constitutes an electro-magnetic solenoid. The coil may be formed and bound in the shape of a hank, as shown in this figuroj or the wire may be wound over a hollow bobbin, and tliis fixed to a base. It is necessary to thus construct a solenoid if it is to be used in drawing a core of iron into itself. The property of all solenoids is that of a sucking action on cores of iron free to move into them. That is to say, if a core of iron is suspended in a vertical position over or under an open solenoid, and within the sphere of its attraction, the core of iron will be sucked into the coil when a sufficiently strong electric current is sent through the coil. Experiment a. To demonstrate this sucking property of a solenoid by means of an experiment, wind several turns of insulated wire (say No. 24 silk-covered coppbr wire) over a hollow boxwood bobbin with thin sides, and a smooth bore of | or J-inch ; fix this solenoid to a suitable stand, and suspend close over its mouth a short rod of soft iron by means of a thin spiral spring. On sending a strong current through the coil of the solenoid, the iron will be drawn into the coil against the pull of the spiral spring. If the short iron rod is suspended beneath the coil by a filament of silk or of cotton passing through its interior, so as to have only j-inch of iron inside the lower mouth of the solenoid, it will be drawn up into the coil whenever a strong current is sent through the wire. The electric hammer shown at Fig. 45 (a popular toy, fully described and illustrated in Amaieiir Worh, Vol. II., New Series, and in Work), is constructed on this principle. The hammer is con- 60 ELEOTBIGAL EXPEBIMENTS. structed on tho model of a Nasmyth steam hammer, with a soft iron piston working in a brass cylinder wound with some three or four layers of silk-covered wire. When a current from four Bunsen cells is sent through this coil, the piston is sucked up into the solenoid, and in so doing moves a lever which discon- nects the current and allows the hammer to fall. In UlIXEUt -^^=^& Fig. 45. Bowron's Electric Hammer. falling it strikes the lever, and again closes the circuit, and in this way the up and down motion of the piston is ensured. This model electric hammer is sold by Mr. G. Bowron, Praed Street, London. The suckinsr action of solenoids has also been utilised in regulators for such electric arc lamps as the Pilsen lamp, and in the con- EXPERIMENTS WITH ELEOTBO-MAGNETS. 61 struction of ammeters and similar measuring instru- ments. b. The solenoid has also some other interesting pro- perties. As might be expectedj from the fact that its hollow core of air has similar polar extremities to those of an electro-magnet made of iron, these poles behave much the same as those of a magnet, the north pole of the solenoid repelling the north pole of a permanent Fig. 46. Apparatus for showiug the Magnetic Poles of a Solenoid. magnet, like poles of two solenoids repelling each other J and solenoids, free to move in the magnetic meridian of the earth, place themselves with their ends pointing due north and south, thus showing that they are subject to the directive influence of the earth's magnetism. c. A Helix of wire will serve the pui'pose in experi- ments with solenoids to demonstrate their magnetic 62 ELEGTBICAL EXPERIMENTS. properties. A helix is a hollow spiral of wire, like a spiral spring, obtained by winding a smooth cylinder (such as a pencil or ruler) with wire, and slipping the coil of wire off when wound. Silk-covered copper wire of from No. 20 to No. 24 gauge will be found most con- venient for this purpose. A helix of wire thus formed, and furnished with connecting sockets at the ends, is shown at Fig. 47. An interesting experiment may bo performed, according to Professor A. Bain, with a helix thus constructed and arranged, which will serve to illustrate magnetic suspension. If a small steel perma- Fig. 47. nent magnet is inserted in such a helix, and a strong current of electricity is sent through the wire, the bar magnet will rise and take up a position in the middle of the helix, as shown in the figure. d. When such a helix is suspended to a frame, as shown at Fig. 46, with the terminals of the solenoid dipping into cups or troughs containing mercury, a current of electricity can be sent through the helix, converting it into a magnet, which is then free to move and take up a position pointing north and south, as an ordinary magnet. e. A very interesting experiment may be easily per- EXPERIMENTS WITH ELECTRO-MAGNETS. 63 formed with a helix of fiae copper wire not insulated. Connect one end of the wire helix to a horizontal arm of metal in contact with one pole of the battery, and allow the lower end of the helix to lightly dip into a metal cup containing mercury, connected to the opposite pole of the battery. On sending a current through the helix, its coils will be seen to contract, and the lower end will be drawn out of the mercury, thus breaking the electric circuit. When the current ceases to pass through the helix, its coils agaiu expand and drop the Fig. 48. Divided Iron Ring. lower end agaiu into the mercury cup. This completes the circuit, and the same movement is repeated, thus making and breaking the circuit by a jumping motion of the coils. This interesting movement of the helix is caused by the mutual attraction of the coils when a current is passing through them, and is utilised iu con- structing contact breakers for induction coils. § 21. Magic Magnetic Rings. An amusing and interesting experiment, illustrating the attractive influ- ence of solenoids and their magnetic power, may be 61 ELECTRICAL EXPERIMENTS. performed with a magnetizing coil, as shown at Fig. 12, § 7, and an annealed iron ring divided into two equal parts with a hacksaw, as shown at Fig. 48. Thus divided, the two halves will perfectly fit each other, and this is necessary to the success of the experiment. The divided ring is then fitted together inside the wire coil and the two ends of the coil are connected with a powerful battery. The magnetized iron of the ring will keep the halves together whilst current is passing Fig. 49. Magic Magnetic Bing. through the coil, but the whole will appai'ently break in pieces when the circuit is broken. If a large iron ring — say of 1 inch round iron and 6 inches in diameter — is prepared as shown in Fig. 49, and a coil of some forty or fifty turns of No. 18 cotton- covered copper wire, some amusement may be caused by inducing a lad, not in the secret, to lift a heavy weight with the ring whilst the coil is connected in circuit with a strong battery. Whilst he is still lifting the weight, break contact with the battery, and he will EXPERIMENTS WITH ELEGTEO-MAGNETS. 65 appear to have broken the ring. Or get two lads to each hold a half of the ring and gently pull, then sud- denly break contact, and note their consternation at the broken ring, § 22. Magic Magnetic Hemispheres. This experi- ment, together with that mentioned in the last sec- Fig. 50. Magic Magnetic Sphere. tion, is a modified form of one published in 1847, and reproduced in " Electric Toy Making." The experi- ment is performed with two hemispheres, or cups of annealed iron, each fitted with an annealed soft iron core, one of which is furnished with a coil of wire, as shown in section at Pig. 51, thus forming an electro- 66 ELEOTBWAL EXPERIMENTS. magnet. The ends of the coil of wire may be brought through holes drilled through the crown of the hemi- sphere, as shown in the sketch, or brought out through two slots out in the rims. The two hemispheres should be furnished with rings, as shown in Fig. 50, and the coil placed in circuit with a powerful battery. If every part has been well fitted, some amount of force will have to be used in pulling the two cups apart when Fig. 51. Section of Magic Maguetio Hemisphere. current is passing through the coil, but they will sepa- rate easily when the circuit is broken. § 23. Uses of Electro-Magnets. These are nume- rous, and would fill a long list, since a large num- ber of electrical instruments owe their usefulness to electro-magnets. Horse-shoe electro-magnets are em- ployed in the construction of electric bells. A full description of these is given in " Electric Bella : and All About Them," a book published by Messrs. Whittaker & Co. at the price of three shillings. Electro-magnets EXPERIMENTS WITH ELEGTRO-MAQNETS. 67 in several forms are employed in the construction of dynamo-electric machines. These are briefly described by Mr. Bottone in " Electrical Instrument Making for Amateurs/'/ and more fully in another book by the same author, on " The Dynamo : How Made and Used." Fig. 52. King, Mendham & Co.'s Electro-Motor. Electro-motors, are machines constructed with electro- magnets. These are described in a little volume by Mr. Bottone on " Electro-Motors : How Made and Used." ^ The cores of induction coils are electro- magnets, and also the automatic breaks of these in- struments, described in the author's book on " Induction Coils." ^ The Morse sounder, which has worked a complete revolution in telegraphy since its introduction, is also an electro-magnet. ' All these books are published by Whittaker & Co. CHAPTER III. EXPERIMENTS WITH INDOCTION COILS. § 24. Spark Induction Coils. . It has been shown in the previous chaptei'j that an electric current passing through a wire conductor^ develops therein a magnetic condition which exerts an influence on the air surround- ing the wire, converting it into a magnetic shell. It has also been shown that this magnetic influence is transmitted to another wire conductor running parallel to the current- carrying wire^ if the two wires are placed close together without touching each other. If the current-carrying wire is wound in the form of a helir, each turn increases the electro-motive force of the current passing through the wire, because each turn magnetizes a core of air, and the magnetic influence of this is transmitted to the neighbouring turn of wire. If an insulated wire is wound over the helix of wire in the same direction, a much stronger magnetic influence is felt, so to speak, in the second or outside helix of wire than would be experienced if the two wires were merely laid along parallel in straight lines side by side. If the wire helix is wound over a core and doubled on itself so as to form a double helix, and many folds of a much finer wire is wound over this, a current of very high ISXTEBIMENTa WITH INDUCTION COILS. 69 tension is induced in the secpnd wirej and a coil thus constructed^ is named an induction coil. By properly arranging the wires and adding an apparatus to auto- matically intercept the even flow of the current in the first helix, an induction coil may be built to so enor- mously increase the tension of the induced current in Fig. 53. A Spark Induction Coil. the second coil as to break forth from the ends of this coil in the form of a number of snapping sparks, when the two ends are brought close together. Such an apparatus is named a spark induction coil. This has been fully described and illusti'ated in another book, " Induction Coils," published by Messrs. Whittaker & Co. at the price of thi'ee shillings. 70 ELECTBIGAL EXPERIMENTS. § 25. Experiments with Spark Induction Coils. In the book mentioned in the preceding section, the author could not, for want of space, describe the many experiments which might be performed with spark induction coils. Some of the most simple may be jjerformed with the coil alone, or with the aid of simple home-made apparatus ; but others can only be per- formed by the aid of other apparatus, which must be bought at a high price, or made by the amateur himself. To do the latter, he must know how to work the materials, and this knowledge can only be obtained from detailed and illustrated instructions. These are given in succeeding sections. Some of the most simple experiments with a coil giving an inch spark through air, maybe performed bj'the aid of a Henley discharger, described in the next section. § 26. Experiments with Henley's Discharger. In the ordinary form of spark induction coil, the ends of the secondary wire are attached to two binding screws on the cheeks of the coil bobbin, or on the sup- porting base of the coil. Wires are led off from these screws to the apparatus in use with the coil. One such apparatus is a Henley's discharger, so named after the name of its inventor. This apparatus consists of two vertical pillars of glass or ebonite cemented into brass sockets fixed to the base-board of a coil, or to an inde- pendent base-board, at distances of 6 inches or more apart. Each pillar is furnished with a head of brass or other metal, in which is a hole holding a slide rod of brass or Gei-man silver fitted with an insulating handle EXPERIMENTS WITH INDUCTION COILS. 71 of-elaonite, or (as in the best-made instruments) either a swivel joint or a ball-and-socket joint, holding a similar slide rod. The sliding rods must have insulating handles to protect the operator from violent and danger- ous shocks. The tips of the rods should be made like pencil holders, to hold small pencils of metal wire, and the rods should be so arranged as to be in contact ab their tips when thrust into their socket holders, or when Fig. 54, Henley's Discharger for Spark Coils. deflected at an angle over the operating table placed between them. Pi^ovision must be made for connecting these sliding rods with the terminals of the secondary- wire of the coil, and this is best done in the ferrules of the handles or in the heads through which the rDds slide. In best-made apparatus, a small ebonite table, 3x2 inches, is fixed on an insulating pillar of ebonite or glass, midway between the supporting pillars of the discharger. If the discharger rods can only slide to 72 ELECTRICAL EXPEBIMENTS. and fi'o with a horizontal movement, this table should be fixed to a stem sliding in a hollow pillar arranged for adjustment to any height, but the table may be fixed as shown in Fig. 64, if the rods are furnished with pivoted, or ball-and-socket joints. This table is used to hold substances whilst the spark is passed through them. 1. Deflagration of Wire. Deflagration experiments are among the most simple that can be performed with a good spark coil and a Henley's discharger, a. Fix two short pieces of iron wire in the ends of the dis- charging rods, connect the dischargers to the secondary terminals by two lengths of copper wire, set the coil in motion, and bring the ends of the dischargers together until sparks pass freely between them. b. Lessen the distance between the points until one piece of iron wire becomes white hot, when it will burn vividly and emit bright sparks of burning metal, c. Switch the coil out of action, remove the unburnt iron wire, and substitute copper wire, then repeat the expei-iment, and note the difference, d. Procure specimens of other metal wirps and repeat the experiments with them. Each different metal, and some of the different alloys, will give sparks of a different colour. 2. Deflagration of Metal Filingx. Place a piece of ebonite, or of gutta-percha, on the insulated table be- tween the dischargers, and sprinkle a layer of finely sifted metal filings over the surface, switch the coil into action, and bring the points of the dischargei-s to the edge of the filings on each side. Some of the filings EXPERIMENTS WITH INDUCTION COILS. 73 will be fired, and tlie zigzag spark will receive a colouring characteristic of the metal being fired. Various metal filings should be tried, and mixtures of the several metals will give a variety of results. 3. Deflagration of Metal Foil. Lay a smooth white card or a sheet of smooth white paper on the ebonite table, and place on it a scrap of silver foil. On bringing the points of the dischargers to the edges of the foil, it will disappear with a flash of light, and stain the paper or card. By using a new card with each, this experiment may bo repeated with gold leaf, dutch metal foil, copper foil, and other thin leaf metal, the colour of the flash varying with each metal. 4. Electric Stencils. Place a sheet of tinfoil on the table, and in connection with one of the discharging points. Lay a sheet of note paper on the tinfoil, and bring the other discharger point to bear on the paper. Sparks will pass through the paper and perforate it with cleanly pierced, charred holes. By tracing a pattern or words on the paper with a pencil, and moving the paper under the discharger point to follow the pencil tracing, a stencil may be thus prepared. Thin card may be employed instead of paper, but more time must be allowed for the sparks to pierce the card. A por- table insulated discharger connected to the secondary terminal by flexible wire cord, may be used as a stylus with advantage in this and similar experiments. 5. Electric Stars, a. Lay a sheet of glass on the table, and on this a sheet of tinfoil in contact with one of the discharger points. Set the coil in action, and 74 ELECTRICAL EXPERIMENTS. bring the other discharger point down to the centre of the tinfoil plate within striking distance. The stream of sparks will break up into diverging rays, and per- form a sinuous movement over the tinfoil, h. Remove the tinfoil and slightly moisten the surface of the glass, then bring the points to bear on the moistened surface within striking distance. The sparks will ap- pear to be longer, and assume a zigzag form, whilst here and there they will break up into little points of liffht. Fig. 55. Bent Wires on Ends of Fixed Discharger. 6. Arborescent Figures. Smoke a metal plate until its surface becomes dead black, then lay it on the table with its blackened surface uppermost, and its edge in contact with one of the discharger points. Over the metal plate, place a sheet of clean glass or of mica. Place a piece of wire in the other discharger point, and bend it so as to bring its end vertically on the centre of the glass plate, then surround it with a tiny pool of tvater. When the coil is set in action, this little pool will appear to grow, shooting out branches in all direc- tions, until, after some time, the whole plate of glass or of mica appears covered with beautiful arborescent EXPEBUIENTS WITH INDUCTION COILS. 75 figures. If a plate of glass and a plate of mica are procurable, they may be used alternatelj', different patterns being produced on plates of different material. The patterns may also be varied by employing various acid and saline solutions. This experiment has been named Dr. Wright's cohesion oxperimentj and has been described as such in "Intensity Coils" by "Dyer." If the discharger has not been provided with ball-and-socket joints, or pivoted joints, this and the preceding ex- periments may be performed with wires placed in the discharger points, and bent down, as shown at Fig. 55, or one of the rods may be removed from its supporting pillar, and held in the hand, or supported from a hori- zontal arm over the plate, or a portable discharger rod may be used for the purpose. 7. Fire from Water, a. Connect a length of soft No. 24 copper wire to one of the discharger rods, dip the other end into a glass of drinking water, and bring the end of the other discharging rod near the surface of the water. Vivid sparks will appear to rise from the water when the coil is in action. If a special glass is prepared by drilling a hole through the bottom, and cementing a piece of wire in the hole, and this is secretly connected with the discharger point, the result will appear magi- cal, as if fire was obtained from water. I. To show that water is a bad conductor, and moist air superior to either dry air or water, make a small pool of water (in the shape of a large drop) on a plate of glass, and bring the discharger points down to the margin of the pool on opposite sides. The sparks will pass over the 76 ELECTRICAL EXPEBIMENTS. surface of the water or around the margin of the pool, but not through the water, and they will cover a greater distance than in dry air. c. To obtain a spark through water, and observe it whilst passing through this medium, enclose two platinum wires in a thick insula- tion of gutta-percha well applied so as to avoid pinholes in the insulation. At one end the wires must be left bare for connection with the discharger points, or with lengths of No. 24 copper wire leading from them ; the opposite ends must be covered up to a mere speck or Fig. 50. Apparatus for Produciug Sparks under Water. tip of platinum. The two wires must now be mounted in a cork bung or in the wooden stopper of a wide- mouthed glass jar, the two covered ends of the wires being bent to within striking distance of each other ; that is to say, nearly touching each other, as shown at Fig. 56. When these are immersed in water, and the coil set in action, vivid sparks will pass from one point to the other through the water, d. The interest felt in this experiment will be increased by enclosino" the platinum wires in two bent glass tubes, and fusino- the glass around their tips, instead of insulating them with gutta-percha, but this can only be done by those who EXPERIMENTS WITH INDUCTION COILS. 77 have had some experience in the manipulation of glass. Glass is almost an invisible insulator of electricity, con- sequently the insulation of the platinum wires will not be so apparent as when coated with gutta-percha. 8. Oily Sparks, a. Put a drop of oil on each dis- charger pointj and bring them close together without touching. The sparks will then be intensely green, and their tint be modified by varying the distance be- tween the points, b. Oil may also be employed instead of water to demonstrate the comparative conductivity of these mediums. If a drop or globule of oil be placed on a glass plate, and one of the discharger points brought close to its margin, the static charge of the coil will be manifested by the troubled surface of the oil, which will appear as if in a state of effervescence. On bringing down the other point to the opposite side of the oil-spot, this effervescence will be increased, and flashes of light will appear, but no sparks will pass. After some little time, one side of the oil spot will become dry, and this drying process will go on until only a thin film is left on the plate. This superior re- sistance of oil has led to its adoption as an insulator for the coils of transformers, and also for large induction coils. 9. Supenor Gonductivitij of Hot Air. a. Arrange the discharger points to give the ordinary sparK in air, set the coil in action, and bring a lighted taper near the line of sparks at one side. The stream of sparks will diverge toward the flame, and will lose some of their brilliancy, b. Hold the taper under the stream of 78 ELECTBICAL EXFEBIMENTS. sparksj and allow them to pass through the heated air whilst the points are being slowly drawn farther apart. The superior conductivity of the heated air will be shown by the increased length of spark. Its character will also be changed from the usual violet hue and compact beady form, to a loose flame of a blue tint, c. Bring the points closer together, so as to obtain a fiery red spark, then hold the lighted taper in such a position as to pass the sparks through the wick, when they will become white, and of an ovate form. d. Eaise the taper a little, and separate the points slowly. The sparks will appear to travel around the wick, and form a blue stripe in the flame, e. Smoke the points and bring them close together. The carbon will be- come incandescent, and the two points glow like white stars. /. Blow out the taper and hold the red-hot wick in the stream of sparks. The taper will be immediately relighted, g. Connect one of tlie dischargers with a Bunsen burner by means of a fine wire, and hold the other over the burner, light the burner, bring the point of the other discharger over the flame, and lower the point until sparks are seen to pass from it through the flame to the tube of the burner. Eub two lumps of salt together near the foot of the burner. The flame will change from blue to a brilliant yellow, and will then conduct the sparks better. 10. Modified Forms of Sparks. The form of the sparks from an induction coil may be modified in several ways. a. The stream may be bent out of its course by interposing a piece of thick gutta-percha. EXPERIMENTS WITE INDVOTION COILS. 79 when the sparks will be seen to travel ai'ound the edge of the gutta-percha, b. If the sheet of gutta-percha be thin, and the discharger points brought closer together, the sheet will become softened, and the sparks assume a zigzag form as they pass through it. c. If a piece of copper wire bent in the form of a T or L, is inserted in one discharger, and the point of the other is brought near the copper wire so as to send the sparks against the side of it, they will assume a brush- like form. d. By substituting a wire with a metal bead or ball at the end for the ordinary discharger point, another form of brush spark will be produced, e. If a small concav^e metal shield be soldered to a wire, and substituted for the metal ball, the spark will be again modified in form, and be accompanied by a loud snap- ping sound. /. By blowing on the stream of sparks with a mouth blowpipe, a glass tube, or a pair of bellows, a sheet of flame will be formed on the opposite side, and an appearance produced as of luminous air. 11. Ignition Experiments, a. Place a few drops of sulphuric ether on a tuft of cotton wool, and put this on the small ebonite table between the points of the dischargers. On setting the coil in action and bringing the discharger points near each other with the wool between, the ether will be at once ignited, h. Some lycopodium powder sprinkled over cotton wool may be ignited in a similar manner, and gunpowder may be thus exploded in small quantities, c. If a small tuft of gun-cotton be placed on a wire and held in the stream of sparks, it will explode with a .ieeble report. Only 80 ELECTRICAL EXPERIMENTS. very small quantities of these explosives should be taken at a time. d. A piece of phosphorus the size of a pea, placed on the back of a plate or saucer, may be similarly ignited by the stream of sparks; but I do not advise the experiment, since phosphorus is liable to be inflamed by the hand, when it will cause painful burns which heal slowly, and, the fumes of burning phosphorus are poisonous. 12. Impulsion Sparls. The sparks which pass be- tween the two discharger points from an induction coil, are merely particles of air set in rapid motion by the vibratory action of the force we are pleased to name electricity. The light and heat obtained from these, is due to the friction of the rapidly impelled particles against each other, and against other substances placed in their line of action. If little or no resistance is ofiered to their motion, little or no heating or lighting effects will be observed. To illustrate this fact, place a small quantity of very fine boxwood saw-dust, lycopo- dium, flour of sulphur, or other light non-conducting powder on a plate of opal glass, and form it into a small heap or mound, the size of which must depend upon the length of spark to be used on it, since the diameter of the heap must slightly exceed the length of the spark. Place the points of the dischargers lightly in contact with the margins of the heap on opposite sides, and set the coil in action. The sparks will only set the particles of powder in motion, but will not inflame them. The vibratory action of the current can be readily traced by means of this experiment, the particles EXPERIMENTS WITE INDUCTION COILS. 81 of powder moving as if shaken by the vibrations of the glass. The unequal alternating character of the current is also clearly shown by the disposition of the dust particles. It will be seen that there is a real transfer- ence of the particles across the heap from one side to the otherj but the rate of impulsion is more deter- mined to one side and to one discharger point than to the other. Hence a gap is made in the heap as if the particles were gently blown away from the line of Fig. 57. Mixed Dust Figure. current, and these particles were arranged around one point by the back eddy, whilst a clear space is left around the opposite point. Loose particles of gun- powder alone on the glass will be similarly blown aside by the current without being ignited, but when placed on cotton wool, which offers a resistance to the free movement of the particles, the friction causes heat, and this explodes the powder. G 82 ELECTBICAL EXPEBIMEXT8. 13. Lichtenb erg's Electric Dust Figures. The me- chanical effects of electric impulses may be illustrated by means of vermilion and sulphur dust, and a cake of Fig. 58. Negative Dust Figure. resin or of wax, or a plate of ebonite or of glass. An iron point connected with one discharger of a coil is held over the cake of resin placed on the operating table in connection with the other discharger, and the ■' "'k ! * ''t Fig. 59. Positive Dust Figure. cake is thus charged with electricity. Some vermilion and flour sulphur is then placed in a muslin bag, and the mixed dust shaken on the electrified cake. As the EXPERIMENTS WITH INDUCTION COILS. 83 dust becomes electrified by friction wlieti sliaken from the bag (the sulphur positively, and the vermilion negatively), they take up sepai-ate positions on the cake, and arrange themselves in beautiful figures, diverse in form as they fall on a negative or a positive surface, and diverse in tint from the colours of the mixed powders. Positive spots on the cake will appear Fig. GO. Electric Ga3 Lighter. yellow, and negative spots appear red, whilst in some parts we may observe a mixed spot of red and yellow, with a centre disc of red surrounded by rays of yellow. This experiment can be performed with an electric machine, or the discharge from a Leyden jar, as well as from an induction coil. 4 27. Lighting Gas by Electricity. Place the coil on a table under a gas-burner, and convey two insulated wires (ordinary electric bell wires) from the secondary 84 ELECTRICAL EXPEBIMENTS. terminals of the coil to the burner. Lay bare about 2 inches of the ends^ near the burner and bend them in the form of two horns, with their points within striking distance of each other, as shown at Fig. 60. Test this arrangement before turning on the gas, and arrange the points so as to have a good stream of sparks passing be- tween them. On turning the gas-tap the gas will be lit by the sparks passing between the two wire points on each side of the burner. This arrangement, modified in some of its details, enters into the construction of elec- tric gas-lighters. Care must be taken to keep the con- ductors insulated from each other, and, if the gas-lighter is to remain as a permanency, the discharging points should be of platinum wire. Electric Pistol. Get a 6-inch length of f-inch brass tube, nicely smoothed and polished inside and outside. Mount this firmly on a pistol stock, furnished with trigger and bow complete for the sake of appearance. Drill a 5-inch hole vertically through the brass barrel on top near the stock, and bush this with ivory fitted with a small binding screw furnished with a platinum tip. A similar hole must be drilled through the barrel beneath the stock, and this also fitted with a binding screw tipped with platinum. The two tips of platinum must come near to each other inside the barrel, but must not touch. Fit a cork to the mouth of the barrel as in an air toy pistol. Hold the mouth over a gas-burner, turn on the gas a little so as to fill the barrel with a mixture of gas and air, then securely cork the mouth. Connect two insulated wires from the secondary of an induction EXPERIMENTS WITH INDUGTION COILS. 85 coil to the binding screws above and below the barrel, and set the coil in action. A spark will pass between the platinum-tipped screws, fire the mixture of gas and air, and the consequent explosion will blow out the cork. A model mortar or a model cannon may be similarly fitted for this experiment, as shown at p. 167. A device based on this experiment has been employed to fire the explosive mixture of gas and air in gas engines. Fig. 61. Electric Fusa. § 28. Electric Puses. In § 26, Experiment II, we saw that the spark from an induction coil could be used to fire gunpowder, and the thought naturally occurred, why not employ a current of electricity to fire heavy guns, and explode charges of gunpowder, dynamite, gun-cotton, etc., in large blasting operations ? This has been done on a large scale for many years past, and many devices, named electric fuses, have been invented and patented for the purpose. It is not my intention, in a work of this kind, to describe even a small number 86 ELECTRICAL EXFEBIMEXTS. of the many electric fuses tliafc have been invented, but I will give some idea of the principles of their construc- tion, and show how some two or three varieties may be made by the amateur for purposes of experiment. Electric Cartridge. Get a 3-inch length of india- rubber or gutta-percha tube, or make a strong paper tube and coat it with shellac varnish, india-rubber varnish, or some other water-resisting compound, or in some other way make a water-tight tube capable of holding a charge of gunpowder. Next get two 4-inch lengths of guttapercha-covered No. 18 copper wire, twist them together to form a cable, and fit this half- way into a rubber, gutta-percha, or other water-tight plug fitting into the end of the prepared cartridge case. Separate and clean both ends of the wires from gutta- percha and bend one end as shown in Fig. 61, that is in the form of a pair of horns, with the two ends nearly touching. Place this parb of the cable in the cartridge case, fit the plug in tight, then make it water-tight with varnish. Fill the case with gunpowder, and close the open end with a water-tight plug of gutta-percha, coated with india-rubber varnish. When the cartridge has been made quite water-tight, spread the two free ends of the wires outside, solder them to two longer wires coated with gutta-percha, and cover the joints with some water- resisting varnish. The cartridge is now ready, and may be exploded in a pond by connecting its wires with an induction coil, as the high-tension current will cause sparks to pass between the ends of the wires in the cart- ridge and fire the powder. EXPERIMENTS WITH INBUOTION COILS. 87 StatJiam's Fuse. An imitation of this usef til f ase may be made by constructing a cartridge case as for the pre- ceding experiment, but with the wires inside slightly modified. Procure a G-incli length of No. 20 electric bell line wire, with an inner coating of vulcanised rubber, double this on itself, leaving a small loop or eye at one end. Eemove the outer coating from this loop, but be careful not to injure the inner coating. Cut the wire clean in two with a pair of shears or scissors, and leave a gap of f-inch. Fold a tuft of gun-cotton over this gap, and over the wire still retaining the inner coating of rubbei', then enclose the whole in the case and finish it as already directed. Cliathaia Fuse. An imitation of this fuse may be made by soldering a very fine platinum wire across the gap made in the wire loop of a Statham fuse, all other parts being the same as previously described. This form is more suited to the continuous current from a battery than- the intermittent current from a coil, since the platinum wire must be made hot by the current, and the hot wire fires the gun-cotton or fine gunpowder. § 29. Decomposition Experiments. Although the induced current obtainable from the secondary of an induction coil is intermittent and alternating, or has a backward and forward movement of unequal force and duration when the points of the dischargers are placed close together, or little resistance is interposed between them, this inequality is decreased by resistance, and the two ends of the dischargers are found to be definitely positive and negative. That is to say, the forward 88 ELECTRICAL EXPERIMENTS. movement of the undulations or vibrations from one, is stronger and more pronounced tlian from the other; and the result is a continuous flow of current in one direction. This is illustrated by the power of the in- duced current to decompose water, solutions of salts, and gases. If the alternating movements were equal, there could be no determination of the constituents of a solution in a given direction, and consequently no elec- trolytic action in the solution through which the induced current is made to pass. That the constituents of a solution are carried forward from one element to the other, and there broken up by electrolytic action, is shown in the following experiment. Decomposition of Oopper Solution. Dissolve a large crystal of copper sulphate in warm water — say |-oz. of the copper salt in a teacup of water — and add to it a quantity of sulphuric acid, equal to a teaspoonful. Get two pieces of carbon — fragments of electric lamp carbon are suitable — and suspend them in the solutiou from wires connected to the secondary of the iuductiou coil. On setting the coil in action, it will be seen that metallic copper has been deposited on one piece of cai*- bon, whilst the other is unaffected. This shows -that the copper salt has been carried to one side of the cup and there decomposed, or broken up into its constituent parts of metallic copper and sulphuric acid. The car- bon on which the copper has been deposited is connected to the negative pole of the coil, and the opposite carbon is connected to the positive pole of the coil. Carbon has been selected because it is unaffected by the solu- EXPERIMENTS WITH INDUCTION COILS. 89 tiou, and is cheap. Platinum will serve the purpose equally well; but iron^ steel, and brass are liable to de- compose the solution, and thus mislead the experimenter. Decomposition of WoJer. Procure two 6-inch lengths of guttapercha-covered No. 18 copper wire, bare 1 inch . of one end of each for connection with the coil, and i- inch of the other ends for connection to two platinum wires 1 inch in length. Solder the platinum wires to the bared ends of the copper wires, and coat the joint with gutta-percha, or a water - resisting compound. Fig. 62. Apparatus for Decomposing Water. Bend both wires in the form of S hooks or hangers, with the platinum-tipped turn squarely formed, instead of round, and suspend them in a glass tumbler, with the squarely formed hooks inside, and the platinum tips standing vertical at a distance of 1 inch apart. Now get two glass tubes with a diameter of | or |-inch, in- sert them in a bung or a strip of cork, and place them in the tumbler over the platinum tips, with the tips stand- ing up in the tubes about 1 inch, as shown in Fig. 62. Fill the tumbler with water strongly acidulated with sulphuric acid or with vinegar, and connect the free ends 90 ELEGTIilOAL EXPEIilMEXTS. of the wires with the terminals of the coil. On setting the coil in action, bubbles of gas will be seen to rise from the tips of each wire, and may be collected in suitable receivers placed over the open ends of the glass tubes. Oxygen gas will be given off from the positive pole, aud hydrogen gas from the negative pole, these two gases forming the composition of water. The acid used in this experiment only performs the part of a superior con- ductor to plain water, and is not in itself decomposed by the current. With this apparatus several interesting experiments in decomposition may be attempted with various acid and saline solutions. Even with water acidulated with sulphuric acid, the effects will vary with the quantity of acid present in the water, the distance of the platinum points from each other, their position, and also their shape. The glass tubes over the points may be closed on top if desired, and the platinum points may be enclosed in glass tubes if the experimenter is skilled in the manipulation of glass ; or a glass cylinder may be pierced near the bottom on two opposite sides and the points fused in these holes. Decomposition of Iodide of Foiassium. A verj' pretty experiment in decomposition may be performed on strips of blotting paper dipped in a starch solution and then dried. These strips should be moistened with a weak iodide of potassium solution as required, and placed on a plate of glass in contact with one of the points of a Henley's discharger. The paper should then be touched with the platinum point of the opposite discharger rod, or drawn over it whilst in contact with its surface. The EXP]<:RIMENTS with IXDUOTIOy coils. 91 iodide of potassium will decompose under the influence of the current, and the liberated iodine will unite with the starch, to form iodide of starch, and in doing so cause a purple or brown spot or mark on the paper. If the point is nicely rounded, a pattern may be traced on the paper. ■^ 30. Chargfing Leyden Jars from a Coil. Leyden jars may be charged with a static current of electricity from a good induction coil. The instruments are bottles similar to pickle bottles, coated inside and out- side with tinfoil, and fitted with, ball-pointed rods to conduct the charge. Their construction is fully de- scribed in " Electrical Instrument Making for Ama- teurs," p. 71. They serve as reservoirs of static or high-tension electricitj', and very powerful effects can be obtained from their sudden discharge of the stored-up electric force. To charge a Leyden jar from a coil, place the jar on a slab of glass, ebonite, vulcanised fibre or similar in- sulating substance, connect one of the discharger points to the knob of the jar, and point the other to the outer coating of the jar at some little distance from it. On setting the coil in action, the jar will receive a static charge, and may be discharged in the usual manner with insulated discharging tongs. A Battery of Lei/den Jars may be charged by a large cioil in the following manner : — -Connect the lining of the battery tray by a wire with the secondary terminal of the coil, and connect the knob on top of the battery with one of the dischargers, the other being connected 92 ELEGTBIOAL EXPERIMENTS. to tlie coil. Place the discharger points at striking distance from each other, and set the coil in action. Sparks will pass between the discharger points, and the battery will receive a static charge from the coil. An interesting variation experiment may be tried by con- necting a Leyden jar on an insulated stand as a loop, or in shunt, with a pair of dischargers. That is to say, the outer coating is connected by a wire to one terminal of the coil, and the knob of the jar to the other ter- minal, both discharger points being also connected to the terminals. The Leyden jar forms a supplementary condenser to the coil, and receives a static charge from the secondary coil, much the same as the tinfoil con- denser receives a similar charge from the primary. This charge is discharged across the points in unison with the ordinary discharge from the secondary coil, and thus increases the length of spark and its fiery character. Having seen how Leyden jars may be charged with electricity from a coil, we are now in a position to multiply experiments indefinitely, using the coil with this supplementary condenser (or store) for obtaining stronger effects than could be obtained from the coil alone. With the increased power at our command, sheets of glass may be perforated or broken, and the spark sent through other insulating substances. If the coil is a large one, giving sparks of over 3 inches in length, this glass-breaking experiment may be performed direct, with the coil alone, the glass-piercing apparatus being connected in shunt with a pair of dis- EXPERIMENTS WITH INDUCTION COILS. 93 ctargerSj ia a manner similar to that just described for the Leyden jar experiment. The glass-piercer is simi- larly constructed to that in use with Leyden jars, with this difference, that the piercer should be insulated up close to its point by being enclosed in a glass tube and fixed therein with shellac. All the experiments performable with Leyden jars, detonating panes, and other apparatus for experiment- ing with static electricity, as described in Chapter IV., may now be performed with an induction coil. § 31. Experiments with Electric Sparks in Vacuo. In all the previously mentioned experiments with the induction coil, the induced current has been conveyed from one point to another by a conducting medium. Even when the discharger points have been separated by air-space, the intervening air has con- ducted the current. In the experiments about to be described, we shall see the value of this conducting medium. If we take a tube or a globe of glass, with platinum wires fused in the glass on opposite sides, and exhaust the globe entirely of air so as to obtain a per- fect vacuum, the induced current will not pass between the platinum points, although these may almost touch each other. Some conducting medium must be present in the globe, but this medium may be very highly rare- fied, and beautiful effects follow each variation in the rarefication of the conducting medium. Some of these are shown in the following experiments : — 1. The Dark Tube. Procure a tube of thin glass ^-inch in diameter and 3 inches in length, or an egg- f4 ELECTRICAL EXPERIMENTS. shaped balb of glass, the size of a pigeon's eg^, closed at one end and having a long open stem at the other. Have two pieces of platinum wire fused into the sides of the tube or egg, with their inside points only yVinch apart and 1 inch of each wire outside, then entirely exhaust the tube with a Sprengel air-pump, and seal the open stem by fusing the glass with a blow-pipe flame. The entire operation should be conducted by a person skilled in glass-blowing or the manipulation of glass when heated. On connecting the outside ends of the platinum wires with the discharger points of a coil capable of giving an inch spart or more in air, the sparks will be seen to leap from one platinum wire to the other outsiJe the tube, but will not pass between the points inside, although these are almost touching each other. The inside of the tube> will therefore be per- fectly dark : a specimen of complete vacuity. 2. The Electric Er/g. Procure an egg-shaped bulb of thin glass, the size of a goose egg, or, in other words, an elipsoidal glass bulb, 4 inches by 2^ inches, with short open necks at each end. One end, to form the upper part of the bulb, must be fitted with a brass collar or cap containing a leather stuffing-box, in which a metal rod or piston (some 4 or 5 inches in length) is made to work stiffly so as to form an air-tight joint. The upper end of this piston should be furnished with an ebonite knob, and below this there should be a hole and binding screw, for convenience in connecting the rod by a wire with the secondary terminal of the coil. The lower end of the bulb must be fitted with a similar EXPERIMENTS WITH INDUCTION COILS. 95 cap, furnished ■with, a metal rodj terminating in a smooth knob 1 inch inside the bulb, and furnished with a neck and stopcock, screwing into a hollow foot for connection with the metal plate of an air-pump. By making the Fig. 03. Experiments with the Eleotiic Egg. Various Striie. T piece of the tap thick, and drilling suitable holes therein, a binding screw may be fitted to this part, as shown in the sketch. The two caps must be secured to the glass by shellac or some other strong cement, and the joints made perfectly air-tight. The general ap- 93 ELECTRICAL EXPEBUIENTS. pearance of the finislied instrument is shown at Fig. 63, and the price of one in the shops is from 25s. to 35s. By the aid of this instrument some beautiful experi- ments may be performed with a good induction coil, giving from one to three inch sparks or more in air. a. Connect the egg with the coil, press down the upper rod until the knobs of the two rods nearly touch, then set the coil in action and withdraw the upper rod little by little so as to gradually increase the distance between the poles until sparks cease to pass. Make a note of the distance over which the sparks can pass in a non- exhausted bulb. Decomposition of the air in the egg takes place as the sparks pass through it, and nitrous acid is formed if the egg is perfectly air tight, h. Place the instrument on the metal plate of an air-pump, and exhaust the egg of air to the fullest extent, then put it in connection with the coil, adjust the rods to obtain best results, and note the effects, c. Admit air again to the bulb, place it on the plate of the air-pump, con- nect it with the coil, and proceed in the process of exhaustion by easy stages, noting the different effects at each stage of exhaustion. The length, appearance, and colour of the sparks will undergo beautiful varia- tions with each withdrawal of air, until a certain staee of exhaustion has been reached, when the light will fade altogether. (?. Whilst perfoi-ming the preceding experiments, we shall have noted the spark having a mauve tint when a small quantity of ordinary air re- mained in the bulb. Other gases will produce other tints. A small quantity of hydrogen introduced into the EXPERIMENTS WITH INDUCTION COILS. 97 bulb will give a white light when the sparks are passed through this gas. On exhausting the bulb after each experiment^ and introducing other gases, we can obtain a rose or a deep orange tint from nitrogen, and a pale green from carbon dioxide, e. Another variety of tints and forms may be obtained by the admission of various vapours from volatile liquids, such as alcohol, ether, turpentine, etc., etc. The vapour may be introduced by placing a little of the liquid on a piece of cotton wool, and holding it under the foot of the instrument when exhausted, and opening the stopcock for a moment to admit just a whiS of the vapour. As tl'.o best effects are obtained whenever this vapour-tainted atmosphere is highly rarefied, it may be necessary to withdraw some of it with the air-pump. The bulb must be thoroughly exhausted of one vapour before intro- ducing another. /. The different vapours and gases will not only show a different tint, but will also assume various stratified forms of a most interesting and beauti- ful character. These may be altered by placing the finger of one hand or a piece of wire near the bulb whilst the coil is in action. The glowing striae will assume generally a pencil form and be attracted toward the finger, g. On approaching a strong permanent magnet to this pencil of light, its influence thereon will be immediately apparent, as the pencil will be bent aside by the influence of the magnetic force, and the declination will vary with the pole presented to the light. Experiments in great variety may be tried with different forms of permanent magneta, and also with H 98 ELECTBIGAL EXPERIMENTS. electro-magnets and the electric egg. /(. If electrodes of iron are substituted for. brass, the sparks will be whitOj those from copper, green, from silver, blue, and other metals will also influence the tint of the light in the electric egg. 3. Gassiot's Cascade. This beautiful experiment, the invention of M. Gassiot, was first performed with an Fig. 64. Gassiot's Cascade. induction coil and an ordinary glass beaker placed under the bell-glass receiver of an air-pump. It is now performed by the aid of apparatus specially constructed for the purpose. In appearance this represents a glass vase with a cover, as shown at Fig. 64, but is really a thin glass bulb blown to this form, and enclosing a glass EXPERIMENTS WITH INDUCTION COILS. 99 goblet. Its construction is peculiar^ as will be seen on reference to the figure. The hollow knob of the cover has an electrode of platinum wire blown into the glass and dipping down into a funnel-shaped tube, which forms a hollow stem to the knob. This stem reaches down to near the bottom of the goblet, which rests on the shoulders of the inside of the vase. The stem of the vase is enlarged to form a bulb, and in this is inserted another platinum electrode. When the coil is connected with these electrodes, the current seems to flow, in the form of a stream of light, from the upper electrode down the funnel into the goblet, which first appears to fill with light, then overflow and stream down the sides into the lower bulb. The principles of con- struction here shown are adapted to other forms, and some artists in glass manipulation produce some beauti- ful effects by employing coloured glass in some parts of the apparatus. When the glass is stained with uranium, the stream of flro assumes a green tint, and the goblet appears to glow with a self-luminous green light, which gives it a beautiful appearance. Apparatus thus pre- pared may be obtained from opticians, at prices varying from 5s. to 10s. 6d., according to .size and finish. This experiment obtains additional interest if per- formed with apparatus constructed by the amateur on lines similar to those adopted by its inventor. To con- struct such an apparatus, we need a good air-pump with an open top receiver, in addition to a good spark coil and accessories. The open top of the receiver should be fitted with a leather stufiing-box, through 100 ELECTEICAL EXPEHIMESTS. which passes a brass rod or piston, as in the electric ^EE previously described. As a substitute, a well-fitting cork bung may be used, with a piece of soft leather glued to its upper surface and pierced with a hole to exactly fit a glass tube enclosing the brass rod, which must be long enough to reach the bottom of the re- ceiver. A goblet must be next secured, and its inside coated with tinfoil to within one inch of the brim. This goblet is then placed on the metal plate of the air-pump (two bits of wire being placed under the foot of the goblet to allow free play of air whilst exhausting the receiver), and the conducting wires from the secondary coil connected to the metal rod on top of the receiver and the metal plate of the air-pump. The metal rod, with its insulating tube, should be pressed down until its rounded end nearly touches the bottom of the goblet, and the receiver be partly exhausted, when the coil may be set in action, and the pump set to work ex- hausting the receiver. As the air becomes exhausted and the vacuum improves, a variety of beautiful surpris- ing effects are produced. At first a faint blue light will appear around the foot of the goblet, this will be- come clearer and brighter, and gradually rise upwards, increasing in brilliancy until it reaches a line level with the tinfoil coating of the goblet, this will then appear to fill from the inside, and the discharge will run over the brim, forming a splendid cascade of fire. Any glass vessel may be substituted for a goblet, but the fiery appearance of the cascade is most effective when seen pouriBg over a goblet's brim. EXPERIMENTS WITH INDUCTION COILS. 101 § 32. Vacuum Tubes. The beautiful effects of an induced electric current in vacuo, are best studied by means of " vacuum tubes," or " Geissler tubes " as they are sometimes named, to honourably commemorate their inventor. These tubes are made of thin glass enclos- ing platinum electrodes hermetically sealed by fusing the glass around them where they enter the tubes. The tubes are then partially ex- hausted of air, and hermetically sealed by fusing the neck of the aperture through which the air has been drawn. The vacuo in these tubes is designedly imperfect. Ex- perience has taught their makers that a perfect vacuum is not desir- able, and it has been found that the best results are obtained when the air or gases in the interior of the tubes is rarefied only to pres- sures which may vary from 2 to 6 millimetres. These tubes may be straight, as shown at Pig. 65, or may be in the form of two bulbs connected by a spiral tube, as shown in Fig. 68, or several such bulbs may be connected by tubes and arranged ^'^S-Jj^. Appearance of . _,, ... StriiE in a Straight in various forms. The straight tube Vacuum Tube. 102 ELECTRICAL EXPEBIilENTS. may also form an outer casing or protection to' a great variety of devices in bent-glass tubing, sacli as letters, arcbitectnral designs, figures of men, animals, birds, etc., some of which are shown in the annexed figures. A still further variety may be. secured by employing stained glass, such as uranium glass, in making the tubes. Beautiful effects may be obtained from rarefied gases, and vapours of volatile liquids hermetically sealed ) I '■'■? V y V Fig. 66. Various Forms o! Vacuum Tubes. in Geissler tubes. For instance, a tube containing rarefied nitrogen will show a brush of red or rose- tinted light at the positive electrode, and a light-blue or violet halo around the negative electrode. With hydrogen the brush is crimson and the halo blue. With carbonic acid gas the brush is green arranged in rings or discs, and the glow a pretty lavender blue in EXPERIMENTS WITH INDUCTION COILS. 103 bright layers. If a tube with contracted middle, shown in Fig. 67, is employed, the colours will be brighter in the nar- row part of the tube, and this form may be utilised for illustrations in spectrum analysis. Another series of tubes may be prepared with hollow bulbs connected by short thin pipes, the bulbs containing mercury, powdered calcium, or some other substances, which are made phosphorescent by the action of the induced current and emit brilliant colours after the current has ceased. A full set of such Geissler tubes would be worth several pounds, the most intricate costing as much as two guineas each, but the simpler forms may be obtained from opti- cians and dealers in electrical goods at low prices, from Is. 6d. each up- ward, according to size and design. As a guide to intending pur- chasers, I herewith append descrip- tions of some forms of Gassiot- tubes and the results obtainable from them. Compound Tubes. These are small vacuum tubes enclosed in an outer ^ifl^/^^^^^^Zt sheathing of glass, the space between Vacuum Tube. 101 ELECTBICAL EXPERIMENTS. the two tubes being filled with a fluorescent solution sucb as sulphate of quinine, which imparts a beautiful coloured margin to the stream of light passing through the inner tube. Convoluted Tubes. These resemble the compound tubes in their construction, the sole difference being in the form of the outer casing, and the convoluted tube •^^y^^/^m^fK^^ Fig. 68. Various Forms of Vacuum Tubes. enclosed in it. The convoluted tube ends in two bulbs each fitted with platinum wires, and the outer casing is shaped to suit the form of the convoluted tube. The space in the outer casing ai'ound the inner tube and between the terminal bulbs, is filled with a fluorescent solution. The inner tube is sometimes made of tinted glasSj and wrought into such forms as that of a cross, a crown, a star, or figure of flower or animal. In some, EXPERIMENTS WITH INDUCTION COILS. 105 the inner tube is twisted in the form of a spiral or zig- za.g, in others a compound is formed of alternating short pieces of zigzag or spiral tube, and small bulbs conr nected together. In some, the outer containing case is mounted vertically on a broad foot or stand, whilst in others the case is mounted in a horizontal position. The latter position is generally chosen when the outer case o^^~ n^^oo<^orr ^2^ ^ O &D Ph Jj O 3 ^^ d ' 5 g ai >• ID > .H ^ -^ O 03 P 0) 3 ^ EH - -^ Sot) c3 a Pi c3 c« 1^ o pi p cq H 02 CQ ^ S I o • A ■ SI, a PI o, ffl 2 cj •3 DO OOP, ooo.S o -^3+3^ -i3-0-L343 -J3 'm 'ot W m 'm "m m m OOrJ OOOO.O Q, B-.S . ft. Ph O- Ph - Pi QJO^ "OJOJOtU oj PPH PROfi R ri S 1 o 02 O fig .2 O O M^q N N i^ »lDOa3(Br3a,(B(D° o -gr| ^ -JlrS P-ll -g O PQ ,a 'tl "S ^ 'S fe C S js cs 'o.oSp.Spoop.-jH -BsltsrSss-aJ mot^icQOoaQOcQ-*) ns id 'd •^ ., -iH ••-( ., o ~ . o o - . 2 . 2 .2 a 2 ii ■ § ■■5 g - .2 ^ £ (5 2 - -S :. H M ^ o! Pq o W «2 O O (D 4) ^ G3 ir;3 '■ t^ p p PROP R >, . S -a ■^ 2 ^ *H . 3 <1 fq m OOQ H N ELEOTBOLYTIO EXPERIMENTS. 217 It is possible in some cases to dispense entirely with a porous partition when conducting experiments, the two liquids being separated by the difference in their specific gravity, the heavier liquid being poured into a tall glass first, and the lighter liquid so introduced as to float above the first. This may be done by floating a cardboard disc on the first liquid, then pouring the second carefully on this. When thus arranged, we may witness the interesting experiment of one metal being dissolved by the upper layer of liquid whilst the lower part of the same rod is receiving a deposit. The results of such an arrangement in some experiments performed by Mr. Gore, are shown in tabular form on the opposite page. If we employ a glass trough divided iuto two equal compartments by a partition of porous earthenware cemented to the sides of the glass vessel, the range of experiments may be extended to such metals as gold and platinum, on which a deposit of the baser metals may be obtained when one end of a bent rod of gold or of platinum is made to dip into a solvent solution on one side and a strong solution of the base metal on the other side of the partition. Cyanide of potassium is a solvent for gold, and aqua regia a solvent for platinum. The process of electro-deposition known as the single- cell process, is, however, carried on generally by means of a compound cell consisting of a large containing outer cell holding the solution of the metal to be de- posited, and an inner cell of porous earthenware hold- ing the solvent solution and the metal to be dissolved 218 ELEGTEIGAL EXPERIMENTS. to furnisli the electric current. In this arrangement the two liquids touch each other through the pores of the cell, but do not mix, and the two metals are con- nected by a wire above the liquid, and thus complete the circuit. The cells of the batteiy known as the Daniell battery, invented by Professor Daniell, are thus constructed. In the original arrangement the outer cell was con- structed of copper, but in the modern modifications of his invention, the outer cell may be of stoneware, porcelain, or glass, and the negative element (copper) contained therein be of any form, either a cylinder surrounding the porous pot, a plate, or a rod, as may suit the convenience of the maker. It is best, however, to have a large negative surface, and therefore a cylinder of copper makes the best negative element. This must be immersed in a saturated solution of copper sulphate, and provision must be made to keep the solution in a saturated condition by suspending therein a bag containing crystals of the copper salt, which dissolve gradually and so maintain the density of the solution. The positive element (zinc) is con- tained in a cell of porous earthenware immersed in the copper solution. This cell is charged with dilute sul- phuric acid, which enters into combination with the zinc, forming zinc sulphate, and furnishing, when the two elements are connected, a current of electricity, having a potential of a trifle over one volt. As this force is quite enough to decompose a solution of copper sulphate, it not only deposits copper on the negative ELECTROLYTIC EXPERIMENTS. 219 element of the battery, but also furnishes enough current to decompose a solution of this salt in a separate vessel. As this force will also decompose gold and silver solutionSj and is constant for long periods, the Daniell battery is esteemed one of the best generators of electricity for the purposes of electro- deposition. § 59. Electrotype Experiments. If we remove the coi^per plate or cylinder of a Daniell cell, and substi- tute a copper coil, brass medal, or other metal article connected to the zinc, it will (provided it is electro- negative to zinc) be coated with a deposit of copper. If the coin is soiled with grease, oil, or other animal substance before being placed in the solution, the de- posit of copper will not adhere firmly to the coin, but may be peeled off when it h.as attained the thickness of paper. The inside portion of this envelope will then be found to have taken an exact impression in reverse of the features of the coin which it covered. The dis- covery of this fact by Mr. Spencer in 1836 led to the invention of the electrotype process of duplicating de- signs in copper. By this process any artistic design cut, or engraved, or stamped, or cast on any metal, or other substance, may be exactly reproduced in the most minute detail in copper. It has received the name of electrotype, because a forme of printing type may be exactly copied, and the copy used instead of the original for printing the book. Although the process may be put to such uses, it is rarely if ever thus employed at the present day, as it is more costly than the equally 220 BLEGTBICAL EXPEBIMENTS. effective stereotype process of duplicating formes of printing type. The chief employment has been in tlie duplication of engravingSj for whicli it is eminently suitable. The engraved wood block, or other design to be copied, is first reproduced in wax or in gutta-percha, or a similar plastic material whicb will take the fine lines of the engraving, and this copy is then carefully coated with blacklead to render its surface capable of conducting the electric current and receiving a coat of copper. Copper is then electro-deposited on -this mould until the film of metal is deemed to be thick enough, when it is removed and backed with type metal, and mounted on a type-high wooden block for the printing- press. As some experiments illustrative of this process will be found of spme interest, I give a few directions foi* their performance. 1. Mectroti/pe of a Medal or Coin, Valuable coins, however old, may be exactly duplicated in copper by the electrotype process. For coin cabinets, where it is desirable to keep the valuable coins under glass to pre- serve them from the fingers of connoisseurs, and yet show them both on the obverse and reverse side, this method of duplication has several advantages. Copies of both sides can be taken and backed to the required thickness, then cemented by their backs to the case under the glass, and thus be shown to friends side by side with the real coin. If the coins are of silver or of gold, the appearance of the original may be reproduced by gilding or silvering, directions for doing this being ELEGTBOLYTIO EXPERIMENTS. 221 given further on. The mould for duplicating coins, may be made of wax, of gutta-percha, of plaster of Paris, or of fusible metal. a. To make a mould of gutta-percha, heat some of this material in scalding hot water until soft, roll it into a ball, press the ball on the centre of the coin, and work it with the finger and thumb until it forms a cake all over the coin and down over the edges, then put the coin on a bench, and a piece of metal heavily weighted on the gutta-percha at the back. Allow this to get quite cold and hard before removing the weights, h. To take a mould in wax, get some good beeswax and soften it by heat (and by working in the warm hand) until it is soft enough to be worked over the coin, as with the ball of gutta-percha, then set aside to cool and harden. It is advisable to lightly oil the coin before pressing on the gutta-percha or wax, to prevent these substances from sticking to the coins, c. To take a mould in plaster of Paris, get a cardboard tray large enough to hold the coin, and some good plaster of Paris. Oil the coin and place it in the box. Mix some plaster of Paris with water to the consistency of cream, and pour it in the box on the coin, stirring all the time with a feather to break up air-bubbles, then set aside to harden. "When quite hard, remove the coin and gently dry the mould for several hours. When the mould is dry, bake it in an oven, and dip it whilst hot in linseed oil, then set aside for the oil to oxidize and harden. The mould should be treated two or three times like this, so as to get the oil well into the plaster, 2-22 BLEGTRICAL EXPERIMENTS. and tlius prevent it from absorbing water, d. Fusible alloy, fusible metal, or "clichee" as it is sometimes named, is an alloy of tin, lead, and bismath in the following proportions : — Tin. Lead. Bismath. 1. 1 part. 1 part. 2 parts. 2. 3 parts. 2 parts. 5 „ 3. 1 part. .. 2 „ 3 „ 4. 3 parts. .. 5 „ .. 8 „ Any of these will melt at the temperature of boiling water. Place the coin in a shallow metal tray, just large enough for the mould, and make both warm by placing them on a hot iron. Melt the alloy in a ladle or an old iron spoon, and pour it in the tray on the coin, then set aside to cool and harden, e. Other plastic sub- stances and other methods may be employed, in fact anything that will take a clear impression of the coin, including stearine, paraffin wax, marine glue, sulphur, sealing-wax, shoemakers' wax, and gelatine. Wax may be melted and run into a tray on the coin, or made as directed for fusible metal^ A mixture of white-lead and beeswax (one ounce of white-lead to one pound of wax) is superior to wax alone. Of all these substances, gutta-percha is the best for the purpose, and plaster of Paris the most troublesome. An electro of a coin may be taken direct by coating the face W^ith a very thin film of oil or of blacklead, and bedding one-half depth of the back in a cake of wax, having first laid a copper wire on the wax to be pressed in with the coin to form a metallic connection. A shell of copper is deposited ELEGTROLYTIC EXPERIMENTS. 223 on the face of the coin, which is then removed and the obverse side similarly treated. As the oil on the coin will prevent adherence of the copper shell, this may be removed from the coin, and will be found to be a copy of the coin. Moulds of wax, gutta-percha, plaster of Paris, and similar non-conducting materials must be made conduc- Fig. 136. Single-Cell Apparatus for Electrotype. tive by coating them with best blacklead. First embed in the face of the mould, near the rim of the impression, the end of a thin copper wire, to hold up the mould in the solution, and to form a connection between it and the zinc in the porous cell. Then, with a soft brush, such as a sable or camel-hair brush, and finely powdered blacklead, brush the face of the mould until it has been fully coated and well polished with blacklead, some of which must also be brushed around the end of the copper wire to connect it with the blackleaded surface 224 BLBGTBIGAL EXPERIMENTS. of the mould. The mould should then be weighted with a scrap of lead to sink it in the copper solutioDj and suspended in the outer cell connected to the zinc of the inner cell of a Daniell battery, as shown at Pig. 136. After several hours, the shell of copper will be thick enough to be separated from the mould. This must be carefully done if the mould is to be used again, the edges of the shell being raised all around with a thin knife before separating it from the mould. The back of the shell must then be cleaned from bits of wax, etc., and brushed with soldering fluid, then coated with solder to give the shell a necessary stiffness, and the ragged edges sheared off with a pair of stout sharp scissors. This done, some molten solder may be poured in the shell to fill it up to the thickness of the original coin, or it may be filled up with type-metal to the necessary thickness. This backing should be next levelled with a coarse file, and a thin disc of copper, furnished with a loop, soldered to the back. Any medal, seal, engraved or stamped surface of metal or other material, may be copied in a similar manner if the design is not undercut, and is free from projecting or overhanging parts. 2. Electrotypes of Fishes, Ferns, and Leaves. Small fish such as minnows, whitebait, and sprats, maybe copied in copper by a similar process, and then silver-plated to form brooches, ornaments for the hair, and other orna- mental purposes. To take a mould of a fish, half fill a shallow cardboard box with fine sand, and bed one-half ELRGTROLYTIG EXPBliIMJ