CHEMICAL ANALYSIS OF LEAD AND ITS COMPOUNDS SCHAEFFER WHITE •^'••.^-9" Cornell IHnivetstt^ 6f the iWewl^orft State College of Hgrtculture gioi - LC Date Due 1 aWlay J0'53S ^fly 2 «; it7n iS/U ^AV '^ I n/' ^ "CTT I '' / / * >WSSiW8?*''!>"- / L « \y UgMteeaiiM'- ■ 1 I 1 Library Bureau Cat. No. 1137 I QD i37.L5|'5»""""'»"«y Library ^»i?iiMSI??.!?S,',.?"''y*'* °' 'ead and its co 3 1924 002 981 466 The original of tliis book is in tlie Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924002981466 The Chemical Analysis of Lead and Its Compounds JOHN A. SCHAEFFER, A. M., Ph. D. Chief of Laboratory and Director of Research BERNARD S. \yHITE Assistcmt Ghemist PICHER LEAD COMPANY JOPLIN, MO. CHICAGO, ILL. . NEW YORK, N.Y. PITTSBURGH, PA. COPYRIGHT 1912 PICHER LEAD CO. JOPLIN, MO. PREFACE. A review of tlie literature on the analysis of lead and its compounds reveals a multiplicity of methods, many of which are of little value in technical work of today, owing to the many opera- tions entailed and the possibility of error attend- ing every lengthy analysis. The laboratory of today, so closely connected with all lines of manu- facture, must control through chemical analysis every process leading from the raw material to each finished product. It demands extreme accu- racy coupled with rapidity of manipulation. That the best methods combining these salient points are not in general use in many laboratories deal- ing with lead compounds is evidenced from the numerous requests for such which continually reach us. It is with the hope that the methods adopted by the leading laboratories in the lead districts, will prove of some special value, that this work is written. In it will be found certain new methods which retain exactness with considerable conser- vation of time and many others of general adop- tion. Should it aid in increasing the efficiency of any laboratory practice the authors will feel that its mission has been fulfilled. August, 1912. 3 CONTENTS. Page The Analysis op L^ad Ores 7 The Analysis op Sublimed White Lead 15 The Determination op the Apparent Density op Pigments 19 The Analysis op Sublimed Blub Lead 22 The Analysis op Red Lead and Orange Mineral. .25 The Analysis op Flake Red Lead 27 The Analysis op Litharge 31 TSe Analysis op Basic Carbonate op Lead- 35 The Electrolytic Deposition op Lead 44 The Analysis op Pig Lead .' .46 The Iodometric Determination op Antimony and Arsenic in Lead- Antimony Alloys 54 ANALYSIS OF LEAD ORES. The principal ore of lead wMcli will be encoun- tered by the analyst is Galena, the sulphide of lead, PbS. In certain instances Anglesite, the sulphate of lead, PbS04, and Cerrusite, the car- bonate of lead, PbCOa, will reach the laboratory for examination. The constituents usually sought in the analysis of these compounds are lead, zinc and silver, though at times the iron and silicates present must be determined. The value of the ore, however, will depend upon the content of lead, zinc and silver. The ore upon reaching the laboratory is dried at 105°C for several hours and then pulped so as to pass through a 100 mesh sieve. The ore is then ready for examination. Lead. Digest one gram of the sample with 15 c.c. of concentrated nitric acid in a covered beaker. Boil the solution until the brown fumes of the oxides of nitrogen have disappeared. Add 6 c.o. of con- centrated sulphuric acid and again boil until the heavy fumes of sulphuric acid are evolved. Al- low the solution to cool, add 30 c.c. of water and boil. Eemove the beaker from the hot plate and allow the solution to stand for from 7 three to four hours. Filter the solution, washing the precipitate by deeantation three or four times to completely remove the iron. The filtrate is re- served for the determination of zinc. Wash the filter paper used in the previous fil- tration with 75 c.c. of acid ammonium acetate solution made up in the following manner : Ammonium hydroxide (con- centrated) 200 c.c. Water ' 225 c.c. Acetic acid (80%) 250 c.c. . Follow this washing with 75 c.c. of hot water, allowing all the washings to be caught in the beaker containing the residual lead sulphate. Boil imtil complete solution has been effected and de- termine the lead volumetrically in the hot solu- tion by titration with standard ammonium molyb- date solution, as given under the Standardization of Ammonium Molybdate. STANDAEDIZATION OF AMMONIUM MOLYBDATE. Dissolve 8.67 grams of ammonium molybdate in one liter of water. Each c.c. of this solution should be equivalent to one per cent of lead, when a one gram sample is used. Standardize with .2 gram of pure lead foil, pure lead sulphate or pure litharge. Dissolve the lead standard Used in nitric acid, evaporate nearly to dryness, add 8 30 c.c. of water, then 5 c.c. of sulphuric acid, specific gravity 1.84, cool and filter. Dissolve the lead sulphate in 150 c.c. of acid ammonium ace- tate made up of the strength as above given. Dilute to 200 c.c. with hot water, boil and titrate with the standard ammonium molybdate, using an outside indicator of 1 part of tannic acid in 300 parts of water. The appearance of a yellow color indicates an excess of ammonium molybdate. It has been found that a correction of .7 of 1 c.c, of the titration volume must be deducted as a blank to allow for the sensitiveness of the reac- tion. The following precautions must be observed in carrying out this method: Calcium forms a more or less insoluble molyb- date, and when calcium is present results are apt to be high. However, when less than 2 per cent of calcium and a high percentage of lead are pres- ent, there appears to be no interference from the calcium. This method is only applicable to sam- ples containing more than 20 per cent of lead. Should a lower percentage of lead be present it may be determined by the bichromate method or weighed as the sulphate. BICHEOMATJ! METHOD FOE THE DETBEMIITATION' OP LEAD. Treat one gram of the sample with concentrat- ed nitric acid, evaporate to dryness and cool. Take 9 up the residue witli 75 c.c. of a solution made up in the following manner : Acetic acid (80%) 255 c.c. Ammonium hydroxide (con- centrated) 150 c.c. Water 595 c.c. Boil gently for a short time, filtet, and wash well with boiling water. Treat the filtrate with sufficient neutral potassium bichromate to precip- itate aU the lead, boil, filter and wash with hot water until all the uncombined potassium bichro- mate is removed. The above conditions must be carefully watched, as a slight deviation may re- sult in the formation of a basic lead chromate. The ready formation of this compound has pre- vented the general adoption of this method. Dis- solve the lead chromate in dilute hydrochloric acid (1:1), using as little of the acid as possible. Titrate the chromic acid present in the solution with ferrous ammonium sulphate, having an iron value of .0025, using a two per cent, solution of potassium ferrdcyanide as an outside indicator. It is necessary to deduct .5 of one c.c. of the fer- rous ammonium sulphate for each 75 c.c. of solu- tion used, as the amount required for the sensi- tiveness of the reaction. 10 Calculation. The percentage of lead may be determined di- rectly by dividing the number of c.c. of ferrous ammonium sulphate used by the factor 3.25. This factor is determined by the following equations: K,Gv,0, + 6 Fe SO* + SH.SO* = 2KHSO4 + Cr,(S0.)3 + 3 Fe,(S04)3 + 7 H,0. 2 PbCrO.=-2 Pb + CraOe. ' Crj Og is equivalent to 6 Fe. 2 Pb is equivalent to 6 Fe. 414 is equivalent to 336. Factor from iron to lead equals 1.23. Strength of solution equals .0025 Fe. .0025 equals % of .01%. 4.00 divided by 1.23 equals 3.25. The number of c.c. of ferrous ammonium sul- phate used divided by 3.25 gives the percentage of lead present when a one gram sample is used. The lead may be calculated directly from the amount of iron titrated by using the factor 1.23. SULPHATE METHOD FOE THE DETBEMINATION OP LEAD. Details for the gravimetric determination of lead as sulphate are given under the analysis of Basic Carbonate of Lead on page 35. Zinc. Add 8 grams of ammonium chloride to the fil- trate and washings from the lead sulphate pre- cipitate. Eender the solution alkaline with am- 11 monium hydroxide, filter off any iron hydroxide which is precipitated, wash, dissolve this preci- pitate in dilute hydrochloric acid, reprecipitate with ammonium hydroxide, filter and thoroughly wash. Combine the filtrates, neutralize the am- monium hydroxide present with hydrochloric acid and add an excess of 6 c.c. of concentrated hydrochloric acid. Dilute to about 250 c.c, heat to about 80° C, add a small amount of sodium sul- phite. Titrate with standard potassium ferrocyr anide as outlined under the Standardization of Potassium Ferrocyanide, using as an outside indi- cator a 5% uranium nitrate solution. STANDARDIZATION OF POTASSIUM FERROCYANIDE. Dissolve 10 grams of pure metallic zinc in hy- drochloric acid. The solution is made up to 1 liter and a volume equivalent to .2 gram is measured out. The remaining solution may be kept for re- standardizing the ferrocyanide solution which, on standing, appears -to change from time to time. In place of using the standard zinc solution, .2 gram of pure metallic zinc may be used for each standardization. The ferrocyanide solution is made by dissolving 43.26 grams of crystallized potassium ferrocya- nide and 7 grams of sodium sulphite in a liter of water. The addition of the sodium sulphite helps to keep the ferrocyanide solution at a constant strength. One c.c. of this solution will be equal to approximately .01 gram of metallic zinc. The indicator is prepared by dissolving ura- 12 nium nitrate in water until a faint yellow color is produced. A 5% solution will usually give a good end reaction. A number of drops of this solution are placed on a spot plate, and the end point is determined by adding to each drop a few drops of the solution which is being titrated. The acid solution containing .2 of a gram of zinc is made faintly alkaline .with ammonium hydrox- ide, using litmus paper to determine the end point. Reacidify faintly with hydrochloric' acid and add 6 c.c. of concentrated hydrochloric acid in excess. Dilute to about 250 c.c. and heat to about 80 de- grees C. The solution is titrated with the ferrocyanide solution until a few drops of the zinc solution give a brownish tinge to the uranium nitrate indicator on the spot plate. As the end point develops slow- ly, it is well to examine each spot after standing for a brief time. The first one developing a brown tinge is taken as the end point. It is necessary to make a correction for the amount of ferrocy- anide solution required to develop a brown color in the uranium nitrate indicator when zinc is absent. This correction is deducted from the total amount of ferrocyanide solution used and will usu- ally run about .5 of a c.c. SilVbe. The treatment of lead ores for the assay of silver depends wholly upon the nature of the 13 ore. The various fluxes used for the formation of the lead button cannot be outlined here, owing to their number ; the analyst desiring to make this determination may readily determine a method of reduction by consulting any standard text on assaying. After the lead button has been obtained the silver may be determined as outlined under the Analysis of Pig Lead. 14 SUBLIMED WHITE LEAD. (Basic Sulphate of Lead.) An average approximate analysis of sublimed white lead as commercially placed upon the mar- ket should show about 78.5 per cent, of lead sul- phate, 16 per cent, of lead oxide and 5.5 per cent, of zinc oxide. The percentage of sulphur dioxide present as an occluded gas, should not exceed .075 per cent., as a higher percentage of this gas causes a deleterious action on any oil in which this pig- ment is ground. Ajtalysis. total sulphates. Mix .5 gram of the sample with 3 grams of sodium carbonate in a beaker. Treat the mix- ture with 30 c.c. of water and boil gently for ten minutes. Allow to stand for four hours. Dilute the contents of the beaker with hot water, filter off the residue and wash until the filtrate is about 200 c.c. in volume. Eeject the residue. By this reaction all the lead sulphate is changed to carbonate, the sulphate being transposed into sodium sulphate, which is found in the filtrate. Acidulate the filtrate with hydrochloric acid and add an excess of about 2 c.c. of the acid. Boil, and add a slight excess of barium chloride solu- 15 tion (12 c.c. of an 8 per cent, solution). When the precipitate has well settled, filter on an ash- less filter, wash, ignite and weigh as BaSO*. Calculate the BaSO* to PbSO* by using the factor 2.6, when a half gram sample is used. Weight of BaSOi X 1.3 equals weight PbS04. On .5 gram sample factor BaSO* to PbS04 = 2-6- LEAD. Molybdate Method. Dissolve 1 gram of the sample in 100 c.c. of an acid ammonium acetate solution made up as fol- lows : Eighty per cent, acetic acid 125 c.c. Concentrated ammonium hy- droxide 95 CO. Water 100 c.c. Add this solution hot and dilute with about 50 c.c. of water. Boil until dissolved. Dilute to 200 c.c. and titrate with standard am- monium molybdate solution, spotting out on a freshly" prepared solution of tannic acid. Details of this method are given under the Analysis of Lead Ores. Ammonium molybdate is a slightly variable salt, but a solution containing 8.67 grams per liter usually gives a standard solution : 1 c.c. equals .01 gram Pb. Standardize against pure PbO or pure PbS04. 16 Bichromate Method. Treat the sample as above described until dis- solved. If the solution is not quite clear, filter. Add to the filtrate an excess of neutral potassium bichromate solution. Boil and stand in a warm place until the precipitate has settled. Filter on a Gooch crucible, or weighed filter paper, Wash thor- oughly, ignite below a red heat and weigh as PbCrO*. The PbGrOi may be estimated volumetrically by titrating the chromic acid present. For this method, dissolve the lead chromate from off the filter with hydrochloric acid. Wash well and de- termine the chromic acid present with a standard solution of ferrous ammonium sulphate, using a dilute solution of potassium ferrocyanide as an outside indicator. The ferrous ammonium sul- phate is made up of such strength that 1 c.c. will equal .0025 Fe. For a one gram sample divide the number of c.c. of ferrous ammonium sulphate used by 3.25. Details of this calculation are given under the Analysis of Lead Ores. Deduct the lead found as lead sulphate from the total lead and calculate the residual lead to PbO. ZINC. Boil one gram of the sample in a beaker with the following solution : 17 Water 30 c.c. Ammonium chloride .... 4 grams. Concentrated hydrochloric acid 6 CO. If the sample is not quite dissolved the result is not affected, as the residue is lead sulphate or pre- cipitated lead chloride. Dilute to 200 c.c. with hot water, add 2 c.c. of a saturated sodium hyposulphite solution and ti- trate with a standard solution of potassium fer- rocyanide, spotting out on a 5 per cent, solution of uranium nitrate as outlined under the Analysis of Lead Ores. Calculate the zinc to zinc oxide. SULPHTJB DIOXIDE. Digest two grams of the sample with frequent stirring in 5 per cent, sulphuric acid for ten min- utes in the cold. Add starch indicator and titrate with N/100 iodine solution. A more accurate method is to add an excess of standard iodine solution to the sample before the addition of the acid and then to titrate the excess of iodine with N/100 sodium thiosulphate solu- tion. Eeport the sulphur dioxide found directly, as it does not exist as a sulphite, but is instead an apparently occluded gas. IKON OXIDE. Determine this constituent as outlined under the Analysis of Litharge. 18 DETERMINATION OF APPARENT DENSITY. The determination of the apparent density and fineness of lead compounds has lately become of special importance in many laboratories where it is essential that the physical properties of these compounds be under control. The method must combine accuracy and rapidity. ' While many methods have been suggested for such control, it has been found that when rapidity is required the most excellent results are obtained through the determination of the weight of a cubic inch of the compoimd. This weight is dependent on two fac- tors, the fineness and the density of the particles. The determination is carried out on a Scott volumeter, modified by replacing the funnel hav- ing a fixed wire screen, with a funnel having an elongated neck, so arranged as to allow the use of various mesh silk bolting cloth. "While not only allowing of numerous determinations on fineness, the difficulty encountered through par- ticles of the compound adhering to the wire screen is eliminated. The apparatus consists of a stand, A, on which is mounted a small tower, B, containing bafiQe plates of glass which serve to evenly distribute the compound under examination. The funnel is divided into two sections, one the funnel proper, 19 Modified Form of Scott Volumeter. 20 D, and the other the neck, E, which fits over the funnel proper and holds the silk bolting cloth firmly in place. The metallic cube is exactly one cubic inch in size. The mesh cloth most suitable for the compound on which the determination is being made is fastened in the funnel. It has been found that a 72-mesh cloth gives concordant results, it being of such coarseness as, in most cases, to allow all the compound to be brushed through the cloth. The cube is placed directly under the bajQQie plates, the compound is placed into the funnel and gently brushed through until the cube is entirely filled. By a rapid stroke with a spatula the excess of the compound is removed, leaving an even cubic inch of the material. The cube and its contents are then weighed and the weight of the cube deducted, giving the weight of a cubic inch of the compound. Several determinations should be made and an average should be taken. Eesults may be ob- tained by this method which vary not more than 3^ of a gram. In the hands of different analysts it has been found that results may vary more than this, due to the personal equation in the carrying out of the method ; however, the method is only a comparative one and enables any analyst to closely check the apparent density of com- pounds in a very rapid manner. 21 SUBLIMED BLUE LEAD. Sublimed blue lead is at tbe present time find- ing its greatest value as an inhibitive pigment for the protection of iron and steel. The high rating given to this pigment on exposure tests conducted under the supervision of the American Society for Testing Materials for the prevention of cor- rosion is bringing it more a,nd more to the at- tention of paint technologists and engineers. In composition it consists of lead sulphate, lead sulphide, lead sulphite, lead oxide and zinc oxide, with occasional traces of carbon. Its color is a pleasing dull steel gray. Analysis. total lead. The total lead content is determined volumetric- ally as outlined under the estimation of Lead in Lead Ores. TOTAL SULPHITE. Treat one-half gram of the sample in a beaker with 10 c.e. of water and a few c.c. of bromine water. Boil gently until all the bromine has passed off. Dilute with water, add another por- tion of bromine water, boil and continue the treat- ment until the sediment has become white in color. Add 8 c.c. of nitric acid, evaporate the solution until the brown fumes of nitric acid have disap- peared, dilute with water and add an excess of sodium carbonate. From this point proceed with the determination of the sulphate as outlined un- der Sublimed White Lead. LEAD SULPHATE. On a separate sample determine the lead sul- phate as outlined under Sublimed White Lead, by transposition of the sulphate with sodium car- bonate. LEAD SULPHITE. Boil one and one-half grams ofthe sample with 3 grams of sodium carbonate, allow to stand, fil- ter and thoroughly wash. To the filtrate add 3 c.c. of bromine water, heat gently to oxidize the sodium sulphite to sulphate and precipitate the sulphate with barium chloride. Filter, wash and weigh in the usual manner. The barium sulphate formed will contain both the sulphur present as sulphate and that present as sulphite converted to sulphate. Deduct the amount present as sul- phate and calculate the remainder to lead sul- phite. LEAD SULPHIDE. Deduct the sulphur present as sulphate and sul- phite from the total sulphur and report the dif- ference as lead sulphide. LEAD CAEBONATE. A small amount of lead may be present as car- 23 bonate. Determine the carbonic acid present as outlined under Corroded White Lead, and calcu- late this carbonic acid to lead carbonate. LEAD OXIDE. Deduct the lead present as lead sulphate, lead sulphite, lead sulphide and lead carbonate from the total lead and report the difference as lead oxide. ZINC OXIDE. Determine the zinc present as outlined under Sublimed White Lead, and report it as zinc oxide. CAKBON AND VOLATILE MATTEE. Ignite the sample in a partially covered cruci- ble at a low heat for two hours. Report the dif- ference as carbon and volatile matter. 24 EED LEAD AND ORANGE MINERAL. These two compounds are oxides of lead, of an approximate formula, PbgO*, being probably a combination of lead dioxide and lead monoxide. They are found on the market as milled oxides and flake oxides. In some instances oxides are found which are artificially colored with organic dyes. The analysis of red lead and orange mineral consists in the determination of the red lead con- tent or the lead dioxide content, moisture, iron, silica, copper and metallic lead. It is also neces- sary to determine from a physical standpoint the apparent gravity or density, which may be done by determining the weight of a cubic inch of the material, as outlined on page 19. MOISTTJEE. Dry 2 grams of the sample for 2 hours at 105 degrees C. The loss will be moisture. RED LEAD, OK LEAD DIOXIDE. Treat 1 gram of the sample in a beaker with 15 c.c. of nitric acid, sp.g. 1.2 (110 c.c. nitric acid, sp.g. 1.42, to 100 c.c. of water). Stir the sample until all trace of red color has disappeared. Add from a calibrated pipette or burette exactly 10 c.c. 25 of dilute hydrogen peroxide (1 part of 3% hydro- gen peroxide to 3.5 parts of water). Add about 50 c.c. of hot water and stir until all the lead dioxide has passed into solution. In the case of some coarsely ground oxides the contents of the beaker may have to be gently heated to effect com- plete solution. After the oxide has completely passed into solution, dilute with hot water to about 250 c.c. volume and titrate directly with a standard potassium permanganate solution, hav- ing an iron value of .005. Titrate to the faint pink permanganate color. A blank titration on the hydrogen peroxide solution must now be made. TITRATION OF HYDEOGEN PEKOXIDE, AND CALCULATION OF BESITLTS. Into a beaker pour 15 c.c. of nitric acid having the strength as above given and add exactly the same amount of hydrogen peroxide (10 cc). Dilute to 250 c.c. with hot water and titrate with standard potassium permanganate to a faint pink color. The difference between the number of c.c. of potassium permanganate required for the blank titration and the number required for the red lead titration is the amount of potassium permanga- nate required for the hydrogen peroxide which was reacted on by the lead dioxide. The dif- ference between the two amounts of potassium permanganate required multiplied by 3.058 gives 26 the percentage of red lead present according to the following proportion : 2 Fe : PbsO. : : .005 : X 112 : 685 : : .005 : X X equals 3.058 To determine the lead dioxide present multiply this difference by 1.067 according to the following proportion : 2 Fe : PbO. : : .005 : X 112 : 239 : : .005 : X X equals 1.067 FLAKE BED LEAD. In certain instances it is found that flake red lead is soluble only with the greatest difficulty by the above procedure. In cases where this dif- ficulty is encountered the following method will be found to give excellent results : Digest 1 gram of the sample in a beaker with 15 c.c. of nitric acid made up of a strength as given in the previous method. Boil the solution for a short time, add 10 c.c. of a standard oxalic acid solution, the strength of which has been pre- viously determined. Add 2 c.c. of sulphuric acid (Id). Boil the solution and titrate with a stand- ard solution of potassium permanganate having an iron value of .005. A blank titration on the same amount of oxalic acid must be made. The 27 difference between the amount of potassium per- manganate required for the blank titration and that required for the red lead titration multiplied by the factor 3.058 or 1.067 will give the content of red lead or lead dioxide according to the pro- portions in the previous analysis. lEOWt This occurs in such a small proportion in all the red leads placed upon the market at the pres- ent time that it can best be estimated colorimetrie- ally. Excellent results can be obtained for the colorimetric determination of this constituent by modifying the method of Thomson.* The very slight quantities of copper which sometimes are found do not interfere with the reaction. One gram of the sample is treated with 10 c.c. of water and just sufficient nitric acid added drop by drop to convert all, the oxide present, except^ ing the lead dioxide, into lead nitrate. Add 10 c.c. of dilute hydrogen peroxide (1:3.5), cover the beaker with a watch glass and boil for a minute to effect complete solution and to convert all the iron to the ferric condition. Wash the contents of the beaker into a 100 c.c. Nessler cylinder, allow the solution to cool, add 15 c.c. of dilute ammonium sulphocyanide solution (1:20), and fJ. I. & E. C, 1912, Sept., ppg. 659. *J. C. S.. 1885, 493. 28 dilute to mark. The intensity of the red color de- pends upon the amount of iron present. This color is now compared with a hlank carried out in the following way : For the blank titration a solution of ferric am- monium sulphate of known strength is required. This is made by dissolving .7022 gram of ferrous ammonium sulphate in water. Add 10 c.c. of sul- phuric acid, heat to boiling and add a solution of potassium permanganate until the iroil is con- verted to the ferric condition. Only the very slightest pink tinge due to potassium perman- ganate may be present, as this pink tinge will fade away, while the presence of any pink color will tend to vitiate the results. Allow the solu- tion to cool and dilute to exactly 1 liter. One c.c. of this solution equals .0001 grams of iron. Pre- pare a blank by placing into a Nessler cylinder 10 c.c. of hydrogen peroxide solution of the above given strength, approximately the same number of drops of nitric acid and 15 c.c. of ammonium sulphocyanide solution. Dilute to 100 c.c, titrate to the exact color developed in the sample of red lead under examination by the addition of the standard ferric ammonium sulphate solution. One c.c. of this solution will equal .01 per cent, of iron when a 1 gram sample is used. It will be found that this method is not only rapid, but that the color can be compared to within .001 per cent, of iron content. 29 COPPER. This constituent is best determined gravi- metrically, as the very slight percentage of other impurities present in red lead tend to interfere in colorimetric methods. Twenty grams of the sample are treated in a large beaker with 50 c.c. of nitric acid, 25 c.c. of water and sufficient hydrogen peroxide to cause complete solution of the lead dioxide. Determine the copper as outlined under the Analysis of Litharge. SILICA. Silica is found to be present in oxides of lead both as free silica and as lead silicate, though usually in inappreciable amounts. Digest 2 grams of the sample in a casserole with 2 grams of potassium chlorate and 15 c.c. of dilute nitric acid. Proceed from this point as outlined under the Analysis of Litharge. OBGANIC COLOK. The adulteration of red lead and orange min- eral with organic coloring matter may be detected by adding 20 c.c. of 95 per cent, alcohol to 2 grams of the oxide, heating to a boil and allowing to settle. Pour off the supernatant liquid, boil with water, allow to settle and add a very small amount of ammonium hydroxide. If either the alcohol, water or ammonium hydroxide are colored, it in- dicates organic coloring matter. The quantita- tive determination is exceedingly difficult and the organic color is usually estimated by difference. 30 LITHAEaE. Litharge, the monoxide of lead, PbO, may contain small percentages of iron, copper, silica, silver and free metallic lead. When the litharge has been made by a process where steam is used, there may be an appreciable amount of moisture present. It appears on the market in two colors, yellow and red. In some instances litharge is fouiid containing a comparatively large percentage of red lead, which in certain uses is undesirable. The determination of each of the foreign constituents in litharge depends largely upon the use to which the litharge is to be put, as in very few cases are all the constitu- ents determined. Analysis, moistukb. Dry 2 grams of the sample at 105° C. for two hours. The loss will be moisture. PEEE METALLIC LEAD. Two grams of the sample are treated in a beaker with hot water and just sufficient acetic acid is slowly added, to dissolve the lead oxide. Stir the solution well and note whether any lead sili- 31 cate remains undissolved. Should such remain, continue stirring until solution has been effected. The solution should never have greater than a 5 per cent, acetic acid strength. Filter the solution and wash the residual metal three or four times by decantation with hot water, having all the wash water pass through the filter paper, which is finally thoroughly washed with hot water. Transfer any "metal on the filter paper to the beaker containing the residual lead, add 1 c.c. of concentrated nitric acid and heat to solu- tion. Dilute with 50 c.c. of water, add 1 gram of sodium acetate and follow this with an excess of saturated neutral potassium bichromate solution, sufficient to precipitate all the lead. Boil, dilute to 100 c.c, allow to cool, filter off the lead ehro- mate, wash thoroughly and determine the lead chromate gravimetrically by drying at 100° C. or volumetrically by titration of the chromic acid present as outlined under the Analysis of Lead Ores. The factor for the direct determination of lead is, however, in this case 1.63, as a 2-gram sample is used. KED LEAD. Determine the percentage of red lead present as outlined under the Analysis of Eed Lead. IBON, Treat 1 gram of the sample with 10 c.c. of water and just sufficient nitric acid, added drop by 32 drop, to cause complete solution. Heat to boiling to oxidize all the iron and determine it colori- metrically as outlined under Eed Lead. COPPEE. Twenty grams of the litharge contained in a 200 c.c. flask are dissolved in nitric acid (50 c.c. concentrated nitric acid to 100 c.c. water). Boil to complete solution. Add 40 c.c. of dilute sulphuric acid (1:1), boil gently for one hour and allow to cool. Filter off the lead sulphate and wash the precipitate thoroughly. Nearly neutralize all the free acid present with ammonium hydroxide, render slightly acid with hydrochloric acid, warm the solution and pass in hydrogen sulphide until no further precipitation of sulphide occurs. Filter off the precipitate without washing, using some of the filtrate to transfer the last traces of sulphide to the filter paper. Dissolve the precipi- tate in a little nitric acid and wash the filter paper thoroughly with hot water. Add 3 c.c. of concentrated sulphuric acid, evaporate until the white fumes of sulphuric acid are evolved and allow the solution to cool. Add a little water and allow to stand for some hours. Filter off the lead sulphate, washing with hot water containing a little sulphuric acid. Heat the filtrate to boiling and precipitate the copper as sulphide with hydrogen sulphide in an ammoniacal solution. Filter off the copper sul- 33 phide through an ashless filter paper, wash, ignite and weigh in a covered porcelain crucible, from which the heat and cover are occasionally re- moved for a few seconds. The precipitate will consist of a mixture of CuO and CujS. Since the percentage of copper is the same in both of these, the copper may be determined by multiplying the amount found by the factor .7988. SILICA. Digest 5 grams of the sample in a covered casserole with 2 grams of potassium chlorate and 15 c.c. of dilute nitric acid (1:1). Evaporate to dryness and dehydrate. Treat the residue, after cooling, with hot water and nitric acid. Heat to boiling, and filter the solution through an ashless filter paper. Wash the residue and filter paper thoroughly with hot acid ammonium acetate solu- tion, made up to a strength as outlined under the Analysis of Lead Ores. Should the residue show a trace of iron, wash it thoroughly with dilute hy- drochloric acid. Complete the washing with hot water, dry, ignite and weigh as SiOa. The residue may be volatilized with hydrofluoric acid, if there is any doubt regarding the purity of the silica. The silica is present as lead silicate and free silica. The above method determines the total content of silica. The free silica may be deter- mined by dissolving the litharge in dilute nitric acid. Heat to boiling, filter, wash, ignite and weigh as silica. 34 BASIC CAEBONATE OF LEAD. (Corroded Wtite Lead.) Basic carbonate white lead (2PbC03Pb(OH)2) contains approximately 80 per cent, metallic lead and 20 per cent, carbonic acid and combined water, witb traces of silver, antimony, lead, and other metals. The analysis of basic carbonate white lead can best be carried out by Walker's method. (a) total lead. "Weigh 1 gram of the sample, moisten with water, dissolve in acetic acid, filter, wash, ignite, and weigh the insoluble impurities. To the filtrate from the insoluble matter add 25 c.c. of sulphuric acid (1:1), evaporate and heat until the acetic acid is driven off ; cool, dilute to 200 c.c. with water, add 20 c.c. of ethyl alcohol, allow to stand for two hours, filter on a Gooch crucible, wash with 1 per cent, sulphuric acid, ignite, and weigh as lead sulphate. Calculate to total lead (PbSO* X 0.68292 = Pb) or calculate to basic car- bonate of lead (white lead) by multiplying the weight of lead sulphate by 0.85258. ' ' The filtrate from the lead sulphate may be used to test for other metals, though white lead is *P. H. Walker, Bureau of Chemistry Bulletin No. 109, re- vised, U. S. Dept. of Agriculture, pp. 21 and 22, 35 only rarely adulterated with soluble substances ; test, however, for zinc, wMch may be present as zinc oxide. "Instead of determining the total lead as sul- phate it may be determined as lead chromate by precipitating the hot acetic acid solution with potassium bichromate, filtering on a Gooch cruci- ble, igniting at a low temperature, and weighing as lead chromate. (b) complete analysis. "When it is necessary to determine the exact composition of a pure white lead, heat 1 gram of the pigment in a porcelain boat in a current of dry, earbon-dioxide-f ree air, catching the water in sulphuric acid and calcium chloride and the car- bon dioxide in soda lime or potassium hydroxide (1.27 specific gravity). By weighing the residue of lead monoxide in the boat all the factors for determining the total composition are obtained. Figure the carbon dioxide to lead carbonate (PbCOa), calculate the lead monoxide corre- sponding to the lead carbonate (PbCOs) and sub- tract from the total lead monoxide, calculate the remaining lead monoxide to lead hydroxide (Pb(0H)2), calculate the water corresponding to lead hydroxide and subtract from the total water, the remainder being figured as moisture. *J. Soc. Chem. Ind., 1905, 24:487. 36 "This method assumes the absence of acetic acid. Thompson* states that acetic acid varies from 0.05 per cent, in Dutch process white lead to 0.7 per cent, in some precipitated white leads. It is then more accurate to determine the carbon dioxide by evolution; this is especially the case when working with a lead extracted from an oil paste, as the lead soap and unextracted oil will cause a considerable error by the ignition method. In determining carbon dioxide by the evolution method, liberate the carbon dioxide with dilute nitric acid, have a reflux condenser next to the evolution flask and dry the carbon dioxide with calcium chloride before absorbing it in the potas- sium hydroxide bulbs. (c) ACETIC ACID. "It is sometimes necessary to determine acetic acid. The Navy Department specifications de- mand that white lead shall not contain 'acetate in excess of fifteen one-hundredths of 1 per cent, of glacial acetic acid. ' Thompson 's method* is as follows : " 'Eighteen grams of the dry white lead are placed in a 500 c.c. flask, this flask being arranged for connection with a steam supply and also with an ordinary Liebig condenser. To this white lead is added 40 c.c. of syrupy phosphoric acid, 18 *J. Soc. Chem. Ind., 1905, 24:487. 37 grams of zinc dust, and about 50 c.e; of water. The flask containing the material is heated di- rectly and distilled down to a small bulk. Then the steam is passed into the flask until it becomes about half full of condensed water, when the steam is shut off and the original flask heated di- rectly and distilled do:wn to the same small bulk — this operation being conducted twice. The dis- tillate is then transferred to a special flask and 1 e.c. of syrupy phosphoric acid added to insure a slightly acid condition. The flask is then heated and distilled down to a small bulk — say, 20 c.c. Steam is then passed through the flask until it contains about 200 c.c. of condensed water, when the steam is shut off and the flask heated directly. These operations of direct distillation and steam distillation are conducted until 10 cc' of the dis- tillate require but a drop of tenth-normal alkali to produce a change in the presence of phenol- phthalein. Then the bulk of the distillate is titrat- ed with tenth-normal sodium hydroxide, and the acetic acid calculated. It will be found very con- venient in this titration, which amounts in some cases to 600-700 c.c, to titrate the distillate when it reaches 200 cc, and so continue titrating every 200 c.c. as it distils over. "If the white lead contains appreciable amounts of chlorine it is well to add some silver phosphate to the second distillation flask and not carry the 38 distillation from this flask too far at any time. ' ' The method used by the chemists of the Navy Department is as follows: Weigh 25 grams of white lead in an Erlenmeyer flask, add 75 c.c. of 25 per cent, phosphoric acid, distil with steam to a ,500 c.c. distillate, add to the distillate some milk of barium carbonate, bring to a boil, filter, keeping the solution at the boiling point (it is not necessary to wash), add an excess of sulphuric acid to the filtrate and determine the barium sul- phate in the usual manner ; subtract 53 milligrams from the weight of the barium sulphate and cal- culate the remainder as acetic acid (BaSO* times 0.515 equals CH3COOH). The object of this rather indirect method is to avoid any error that might arise from fatty acids being carried over by the steam distillation. For white lead that has not been ground in oil, Thompson's method is to be preferred." (d) caebonic acid. The carbonic acid content of white lead may be determined by using the Scheibler apparatus, complete reference to which, with all tables, may be found in "The Analysis of Paints and Paint- ing Materials,"* page 6. A more simple and efficacious m6thod of determining the carbonic *The Analysis of Paints and Painting Materials, Gardner and Schaeffer: The McGraw-Hill Book Company, New York. 39 Carbon Dioxide Apparatus. 40 acid content will be found in the following method : The method can be used in such cases where the substances to be analyzed evolve gases other than carbon dioxide; that is, hydrogen sulphide, sul- phur dioxide, or organic matter. The apparatus used is shown in the accompanying diagram. A weighed sample of the substance is introduced into the Erlenmeyer flask (A). Into flask (B) is placed a 10 per cent, solution of barium chloride, more than sufficient to hold the carbon dioxide evolved, and 20 c.c. of concentrated ammonium hydroxide free from carbon dioxide. If sulphides are present, it is sometimes advisable to pass the liberated gas first through a few c.c. of strong potassium permanganate. ' The flask (B) is warmed until completely filled with ammonia fumes. -Flask (D) is a safety bottle containing the same solution as flask (B). Only in rare cases will any trace of carbon dioxide be noticed in the safety flask. After flask (B) is completely filled with ammonia vapor, make all connections and allow the hydrochloric acid to drop slowly from the separatory funnel into the decomposition flask (A). When effervescence has ceased, heat the contents of the flask until filled with steam. The delivery tubes and sides of the precipitating flask are then washed with boiling water, the flask is filled to the neck, stoppered, and the precipi- 41 tated barium carbonate allowed to settle. Wash thoroughly by deeantation, each time stoppering the flask to prevent any error from the carbon dioxide present in the air, and determine either gravimetrically, by conversion into barium sul- phate, or volumetrically, by dissolving in standard hydrochloric acid and titrating the excess of acid used with standard potassium hydroxide. Calcu- late the barium found to carbonate and the amount of carbon dioxide from the found car- bonate. The entire operation may be hastened by conducting a brisk current of air free from carbon dioxide through the entire apparatus. Two new and rapid volumetric methods for the determination of carbonic acid contents are de- scribed in detail by Leon T. Bonser in the Jour- nal of Industrial cmd Chemical Engineering, March, 1912, page 203, and by H. W. Brubaker in the same journal, August, 1912. A few typical analyses of basic carbonate white lead, for impurities, are given : 42 MfOOOCO V 1) — I UeO U CM CD CM CD 00 iH oioooco c c th CO c t^ lo CO o "-1 00 lOOOiH O O rH OO O i-H O O ^ tH CD OOOO C CO CO COOOOOCM C>0-*00lO U U CD vxn 4) O >/: 05 05 1/3 CO cmiothoj e CO yo coco^oicmio iHOOCO OOO go OiHOOOrtHQO, oooo c coiJo cooooom t^-^t^CD U U 00 1>M U CO -J ■* 03 O CVI OJ>-eMCM e COCO c-<*coO'>»tMCD eoOOCM O OO OO Oi-IOOO-*rf< OOOOCCOCOCOO -OOIO 05iHCM03 u veo u as u co eri »h cm oi oo oococMCM c c -^ CO c^-^O'^Tftio oooeo o OO OO oihootHih'^ OOOO C CO CO COOOOOOJ t>-00Tt(O3 V I) CM U 00 U r-l lO Tt< 03 CO 00 tH CM CM O C C tH CO C t^ C5 tH ■» O lO •*oocM o OO OO ooooo-*«o oooo C CO CO C O O O O O CM i-flOOCM V U tH O CD U CM CM ■<* 1/5 IC O ■^CO^CM C C^ yo C Ttl T(H O O CD CD CMOOi-i o OO So o^oo^i-HO oooo c coiJO coooooco omcMio CO 00 t^ CD tH O O »H OOOC) 1) c o c u 1/3 S8 1) 1> 1/3 1/3 .-( t^ C^ C lil -* O CM 03 lO O O OO O rt< ^ COOOOOCO CM O) '-( t^ 10^003 CM O O iH OOOO u a o a ii CO CO e o U O 00 03 00 C3 CJ3 c o CO o c<3 C3 eo. OCOOOCOCMIO COOOOO"* J3 O U 73 ^ S'c g a 3 W 4-t ^ 1-1 ^^ o -5 s g s -I a-ij « C i2.2rS M O;- o g « «'S S 5.C c U r- c "S. p -w u C aj^ o c"u e ^0.° V, wOUZN2U^i5<:c«U< 43 ELECTROLYTIC DEPOSITION OF LEAD. Lead may be determined electrolytically in a very rapid manner by following the procedure as outlined by Smith* in Ms Electro-Analysis. THE EAPID PEECIPITATION OF LEAD DIOXIDE WITH THE USB OF A BOTATING BLECTEODE. "Twenty c.c. of concentrated nitric acid were added to a solution of lead nitrate, giving a total volume of about 125 c.c. and acted upon with a current of N.D.ioo = 10 amperes and 4.5 volts. The rotating electrode (cathode) per- formed 600 revolutions per minute. The deposits had a uniform, velvety black color. There was no tendency on the part of the deposit to scale off, though more than a gram of the dioxide was pre- cipitated. The time varied from ten to fifteen minutes. A platinum dish with sand-blasted inner surface was used as anode. By using a current of N. D.ioo = 11 amperes and 4 volts upon a solution of lead nitrate containing 0.4996 gram of lead or 0.5787 gram of dioxide, the rate of precipitation was found to be : ♦Electro-Analysis, Smith: P. Blakiston's Sons & Co. 44 In 5 minutes . . 0.4940 gram lead dioxide. In 10 minutes. .0.5708 gram lead dioxide. In 15 minutes . . 0.5747 gram lead dioxide. In 20 minutes. .0.5770 gram lead dioxide. In 25 minutes. .0.5787 gram lead dioxide. In 30 minutes . . 0.5789 gram lead dioxide. The maximum time period for a quarter of a gram of metal is fifteen minutes, and the maxi- mum time for a half gram of metal is twenty-five minutes." 45 PIG LEAD. Pig lead is placed upon the market, both in the refined and crude condition. It will usually con- tain small varying amounts of other metals, such as antimony, arsenic, bismuth, cadmium, copper, iron, manganese, nickel, cobalt, silver and zinc. Refined lead and crude lead are analyzed by the same procedure, save that a 200-gram sample of refined lead is usually required, while a 20- gram sample of the crude lead is ample in most cases. The following methods deal with the analysis of crude lead, for the analysis of refined lead proportionally larger volumes and weights are used. Analysis. The lead is carefully scraped with a bright knife until a clean surface is exposed. The re- quisite amount of lead is removed either by cut- ting off comparatively large pieces with a knife or by filing off small particles with a bright, clean file. Treat the sample with warm dilute hydro- chloric acid, wash thoroughly with hot water and dry, so as to insure the removal of all foreign ad- hering impurities. Weigh off exactly 20 grams and transfer the same to a 500 c.e. Erlenmeyer flask. Add 50 c.c. 46 of concentrated nitric acid and sufficient water (about 25 C.C.) and heat until complete solution has been effected. Add sufficient water (about 60 c. c.) to prevent the separation of any lead nitrate. In certain instances where the lead con- tains a high percentage of antimony a white pre- cipitate may remain. When this occurs, it is re- moved by filtration and washing. The precipitate is reserved for further treatment. Add 20 c.c. of concentrated sulphuric acid, di- luted with water, to the clear lead solution. Boil the solution gently until sulphuric acid fumes are evolved, allow to cool, dilute to 250 c.c. with water and filter off the precipitated lead sulphate. In a lead high in antimony, the lead sulphate precipitate may be contaminated with antimony. In this case the lead sulphate is dissolved in hy- drochloric acid, diluted with water and treated with hydrogen sulphide. The precipitated sul- phides are filtered and treated with yellow am- monium sulphide to dissolve any antimony sul- phide present. The insoluble lead sulphide is removed by filtration. The residue, should any such have remained, obtained in the original solu- tion of lead in nitric acid is added to the filtrate and the combination of the two reserved for future treatment. Warm the filtrate from the lead sulphate pre- cipitation after adding ammonium hydroxide un- 47 til tlie greater portion of the free acid has been neutralized, to about 80° C. and treat with hydro- gen sulphide until no further precipitation occurs. Filter off the precipitated sulphides and wash with hydrogen sulphide water. The filtrate will contain the iron, nickel, cobalt and zinc, while the precipitate will contain the copper, cadmium, bismuth, arsenic, antimony and silver. The later metals are separated according to the method outlined by Fresenius,* the method, however, being slightly modified. The precipitate is gently heated in a beaker, after complete removal from the filter paper, with yellow ammonium sulphide. Filter off the insolu- ble sulphides and wash. Treat the small quantity of precipitate which is insoluble in the yellow ammonium sulphide, after spreading out the filter in a small dish, with di- luted nitric acid (1 part nitric acid, sp.g. 1.2, to 2 parts of water) , at near the boiling point. When the precipitate has dissolved, filter, wash the filter, dry and incinerate, adding the ashes to the nitric acid solution. Add 2 c.e. of concentrated sulphuric acid, evaporate to sulphuric acid fumes, dilute with a little water and filter off any resi- dual lead sulphate. Nearly neutralize the filtrate ♦Quantitative Chemical Analysis, Fresenius, Vol. 2, pages 684-590. 48 with potassium carbonate, then add sodium car- bonate and a little potassium cyanide, free from potassium sulphide, and heat gently. Any pre- cipitated bismuth is filtered off, washed thorough- ly, dissolved in dilute nitric acid and determined by precipitation with ammonium carbonate and weighing as oxide or is fused with potassium cyanide arid weighed as metal. The clear filtrate is treated with more potas- sium cyanide and any cadmium present is pre- cipitated by the addition of a little potassium sulphide. Any silver present will be precipitated with the cadmiurii, consequently the precipitate is removed by filtration, with subsequent washing, dissolved in hot dilute nitric acid and the silver is precipitated by the addition of a few drops of hy- drochloric acid. Filter and evaporate the filtrate almost to dryness and precipitate any cadmium present with sodium carbonate. If any cadmium is precipitated, dissolve it in nitric acid, evap- orate, ignite and weigh as cadmium oxide. To the filtrate from the cadmium and silver sulphides, add a little sulphuric and nitric acids and a few drops of hydrochloric acid and evap- orate until the odor of hydrocyanic acid has en- tirely disappeared. Precipitate the copper in this solution, filtered if not clear, with hydrogen sul- phide, filter, wash and weigh the copper as a 49 mixture of CuaS and CuO as stated under the Analysis of Litharge. Before the copper is pre- cipitated the solution must always be tested for silver, to avoid contamination. The combined solutions containing antimony, as previously stated, and the filtrate obtained from treatment of the sulphides with yellow ammonium sulphide are combined and rendered acid with hydrochloric acid. Filter off the precipitated sulphides. They are examined for arsenic and antimony according to the method of Neher* as follows : The sulphides are dissolved in a solution of potassium hydroxide and oxidized in a casserole, warmed gently on the water bath, with chlorine until all the alkali is decomposed. This requires from one-half to three-quarters of an hour. Any chlorate is decomposed by adding concentrated hydrochloric acid, drop by drop, to the warm solu- tion until no more chlorine is evolved. "When free from chlorate, the acid solution is washed into an Erlenmeyer flask and cooled by sur- rounding the flask with ice. In another flask con- centrated hydrochloric acid (sp.g. 1.2) is likewise cooled. When both solutions are at 0° C, the arsenic-antimony solution is diluted with twice its *Zelt. fur Anal. Chemie., 32-45. Translation from Tread- well and Hall's Analytical Chemistry, 183, 184, Vol. 2 SO volume of the strong hydrochloric acid. Into this cold solution a rapid stream of hydrogen sulphide is passed for one and one-half hours. The flask is stoppered up and allowed to stand one to two hours. The AS2S5 is filtered through a Gooch crucible and washed with hydrochloric acid (1 vol. water to 2 vol. concentrated hydrochloric acid) until 1 c.c. of the filtrate, after being con- siderably diluted with water and tested with hy- drogen sulphide, shows no precipitation. It is then washed with water, and finally with hot alco- hol. After drying at 110° C, the precipitate is weighed as AS2S5. "The filtrate from the arsenic sulphide pre- cipitation is diluted largely with water and satu- rated with hydrogen sulphide. The SbaSs is fil- tered through a Gooch crucible, dried at 230° C. and weighed. ' ' lEOSr, NICKEL, COBAJLT, MANGANESE AND ZINC. The filtrate and washings from the hydrogen sulphide precipitation containing the iron, man- ganese, nickel, cobalt and zinc are rendered alka- line with ammonium hydroxide and treated with ammonium sulphide. Pour the solution into a flask, fill up the flask to the neck, stopper and set aside for at least twenty-four hours and filter. Add acetic acid to the filtrate just to acidity, then ammonium acetate and evaporate at a gentle heat, so that if a trace of nickel sulphide is retained in 51 the solution it will be precipitated with the sul- phur. Collect this sulphur on a filter paper. Treat the precipitated sulphides on the filter paper repeatedly with a mixture of about 6 parts of hydrogen sulphide water and 1 part of hydro- chloric acid (sp.g. 1.2), so that the sulphides may be dissolved with the exception of the nickel and cobalt sulphides. Combine this precipitate with the sulphur precipitate obtained in the above separation and examine them for nickel and co- balt. These sulphides may also be separated by the sodium succinate method as outlined in Tread- well and Hall's Analytical Chemistry. The filtrate containing the iron, manganese and zinc is concentrated by evaporation and finally with the addition of a little nitric acid. Precipi- tate with ammonium hydroxide and filter; redis- solve the precipitate in hydrochloric acid, again precipitate with ammonia, wash, dry and weigh the iron oxide or determine it volumetrically in the usual way. The iron may be determined directly in the sample by following the colorimetric method as outlined under the Analysis of Bed Lead. The filtrate from the iron oxide is treated with ammonium sulphide and allowed to stand twenty- four hours at a gentle heat. Filter off any pre- cipitate and treat it with dilute acetic acid to re- 52 move any manganese sulphide. Determine the zinc gravimetrically or volumetrically as outlined under the Analysis of Lead Ores. Evaporate the acetic acid solution to a small volume and examine for the presence of man- ganese. SILVER. The silver ,is best determined by direct cupella- tion of the requisite amount of metallic lead, this amount depending upon the kind of lead examined. S3 lODOMETEIC DETERMINATION OF ANTI- MONY AND ARSENIC IN LEAD-ANTI- MONY ALLOYS. G. M. Howard* has described a method of sep- arating and determining antimony and arsenic in lead-antimony alloys, which he uses in the labora- tory of the Electric Storage Battery Co. In this method tin does not interfere, making it applicable in the analysis of type metal. Small amounts of iron or copper do not interfere. "Weigh 0.5 to 2 gram portions of the sample in the form of fine filings into dry 125 c.c. Erlen- meyer flasks. Heat the finely divided alloy (it is a good plan to run the filings through a fairly fine sieve) with HCl until action ceases. Remove the fiask from the plate, add about 0.5 c.c. of HNO3 and let stand a few moments until the red- dish color is obtained. Then shake the flask, when the Sb and As will dissolve quickly and com- pletely. Now place upon the plate again and boil vigorously for five minutes or so. "Now, while still hot, pass hydrogen sulphide into the solution until it is completely saturated; 15 minutes is usually sufficient. If insufficient *J. A. C. S., 30, 378 (1908). *C. A., 2, 2348. *J. A. C. S., 30, 1789-90. 54 hydrochloric acid has been used, or the solution has been boiled so long on the hot plate that much has been lost, antimony sulphide will be pre- cipitated as the solution cools. ' ' The hydrogen sulphide treatment is most con- veniently handled by fitting the flasks with two- hole stoppers and inlet and outlet tubes, and con- necting several in series to the generator. If the outlet in the last flask is led into a bottle of caus- tic soda solution, no gas escapes into the room. When saturated the flasks are transferred to a current of air, still in series and again absorbing the gas from the last flask in the caustic soda, and the air passed until all of the hydrogen sul- phide is removed (one-half hour is sufficient for two flasks). The hydrogen sulphide precipitates nothing but arsenic as sulphide, but reduces all salts capable of reduction, antimony, tin, cop- per, iron, etc. The current of air then reoxidizes all these except the antimony, which remains in the antimonious form. "To the now cold solution add a little tartaric acid, and enough water to double the bulk, and filter through a double filter into a one-half litre flask. Practically all of the lead chloride must be washed out of the precipitate with hot water, but it is not necessary to add all of the washings to the filtrate, as the antimonious chloride is readily washed out by decantation with cold water. 55 ANTIMONY. "The filtrate is nearly neutralized by adding powdered sodium carbonate in small portions, care being used not to reach the point of precipi- tation of the lead, or, if this is reached, making it slightly acid again with hydrochloric acid. The neutralization is then completed with sodium bicarbonate and a slight excess added (about one teaspoonful of powder). The antimony is then determined by titrating with standard iodine so- lution, using fresh starch solution as indicator. The precipitate of lead carbonate does not affect the titration, and with a little practice the end point can be recognized just as easily as in a clear solution. Too much starch should be avoid- ed, as it makes the end point obscure. A con- venient strength for the iodine solution is 1 c.c. = 0.005 gram antimony, then with a 0.5 gram sam- ple, 1 c.c. = 1% antimony. "If arsenic is negligibly low, which, with a little experience, can be pretty well gauged by the appearance of the precipitate, or for any reason is not to be determined, the filtering may be dis- pensed with. In this case the whole solution, with the arsenious sulphide, if any, and free sulphur in suspension, is merely transferred to a larger flask, neutralized and titrated. The suspended arsenious and free sulphur are without effect." 56 AKSBNIO. "The bulk of the arsenious sulphide and sul- phur is washed off the filter back into the same flask in which the precipitation was made, using not more than 20 c.c. or so of water. A few drops of sodium hydroxide are added (5 drops of 20 per cent, solution is ample), the solution boiled for a few moments and then decanted through the filter into a 250 c.c. Erlenmeyer flask. This weak soda readily dissolves the arsenious sulphide, while taking up only a small part of the free sulphur. If the amount of precipitate is at all considerable, it is safer to give a second treat- ment with soda solution. "The filter is washed with hot water and dis- carded. To the filtrate is added hydrogen per- oxide solution, which should be reasonably fresh, or else its strength known. Twenty c.c. of 3 per cent, solution is sufficient for arsenic up to several per cent. The hydrogen peroxide oxidizes all arsenic and also all sulphur compounds, giving a colorless solution. This is now boiled down to a small bulk, about 20 c.c, the excess of peroxide being decomposed in the process. When cool, potassium iodide solution is added in amount equivalent to about 0.1 gm. of KI, then 20 c.c. of concentrated hydrochloric acid. After standing five minutes it is cooled and titrated with standard thiosulphate, adding three drops of starch solu- 57 tion only when the color is almost gone. A con- venient strength for the thiosulphate solution is 1 c.c. = 0.001 gm. arsenic, and it should, of course, be frequently standardized. It is well also to run a blank titration, using the same amounts of reagents as in the analysis, to determine whether there is any constant to be deducted from the burette reading, due to impurities in the reagentss. The difficulty with the end point experienced by many in this titration appears to be due to the use of too large an excess of KI and too much starch. With the proportions given above, the end point is exceedingly sharp, and the reaction seems to be just as complete as when more KI is added." 58 Index. A. Page Acetic acid, in basic carbonate of lead 37 Thompson 's method 37 Navy method 37 Antimony, in lead — antimony alloys 56 Antimony, in pig lead 51 Apparent density, determination of 19 Ammonium molybdate method for lead 8 Arsenic, in lead — antimony alloys 57 Arsenic, in pig lead 51 B. Basic carbonate of lead, analysis of 35 Basic carbonate of lead, composition of 35 Basic sulphate of lead, analysis of 15 Basic sulphate of lead, composition of 15 Bismuth, in pig, lead 49 C. Cadmium, in pig lead 49 Carbon, in sublimed blue lead 24 Carbonic acid, in basic carbonate of lead 39 Carbonate of lead, in sublimed blue lead 23 Cobalt, in pig lead 52 Copper, in litharge 33 in pig lead 49 in red lead 30 Corroded white lead, analysis of 35 E. Electrolytic deposition of lead 44 59 F. Flake red lead, analysis of 27 H. Howard method for iodometric determination of antimony and arsenic in lead — antimony alloys 54 I. Iodometric method for the determination of anti- mony and arsenic in lead — antimony alloys ... 54 Iron — in litharge 32 in orange mineral 28 in pig lead 52 in red lead 28 in sublimed white lead 18 L. Lead, bichromate method for 9 Lead, in lead ores 7 Lead, in sublimed blue lead 22 Lead, in sublimed white lead — bichromate method 17 molybdate method 16 sulphate method 16 Lead, molybdate method for 7 Lead, metallic, in litharge 31 Lead oxide, in sublimed blue lead 24 Lead oxide, in sublimed white lead 17 Lead oxide in red lead and orange mineral 25 Lead sulphide, in sublimed blue lead 23 Lead sulphite, in sublimed blue lead 23 Lead sulphate, in sublimed white lead 16 Lead sulphate, in sublimed blue lead 23 60 Lead, total, in basic carbonate of lead 35 Lead, total, in sublimed white lead 16 Litharge, analysis of 31 Litharge, composition of 31 M. Manganese, in pig lead 53 Moisture, in litharge 31 in red lead 25 Molybdate method for volumetric determination of lead 8 N. Nickel, in pig lead 52 0. Orange mineral, analysis of 25 Organic color, in orange mineral 30 iu red lead : 30 Orange mineral, composition of 25 P. Pig lead, analysis of 46 Potassium bichromate method for volumetric de- termination of lead 9 Potassium ferroeyanide method for volumetric de- termination of zinc 11 B. Red lead, analysis of 25 Red lead content, determination of 25 in' litharge 32 in orange mineral 25 in red lead 25 Red lead, composition of 25 61 s. Scott volumeter 20 Silica, in litharge 34 in red lead 30 Silver, in lead ores 13 in pig lead 49 Smith's method for electrolytic deposition of lead. 44 Sublimed blue lead, analysis of 22 Sublimed white lead, analysis of ^ 15 Sublimed blue lead, composition of 22 Sublimed white lead, composition of 15 Standardization of ammonium molybdate for de- termination of lead 8 Standardization of potassium ferrocyanide for de- termination of zinc 12 Sulphate, lead, in sublimed blue lead 23 Sulphate, lead, in sublimed white lead. : 15 Sulphate method, for lead 35 Sulphite, lead, in sublimed blue lead 23 Sulphate, lead, in sublimed blue lead 23 Sulphur, total, in sublimed blue lead 22 Sulphur dioxide, in sublimed white lead 18 T. Thompson's method for acetic acid 37 Total lead, in sublimed blue lead 22 Total lead, in sublimed white lead 16 Total sulphate, in sublimed blue lead 22 Total sulphate, in sublimed white lead : . . . 15 Typical analyses of basic carbonate of lead 43 V. Volatile matter, in sublimed blue lead 24 62 Volumetric methods for lead — Bichromate method 9 Molybdate method 8 Volumetric method for zinc — ferrocyanide method 11 W. Walker's method, for basic carbonate of lead 35 Z. Zinc, in lead ores 11 Zinc, in pig lead 52 Zinc oxide, iu sublimed white lead 17 Zinc oxide, in sublimed blue lead 24 Zinc, potassium ferrocyanide method for 11 63 ■,..'i .i<: . 'Oh'MM.-'y,,::;,, ■^■, ■'"■■■',■ ',,/; . , ■! „ '^,/,X^''""'^-^''if"'"i'''^'<^''"''^'''- ^^-^"K».'?-'.i