THE UNIVERSITY OF ILLINOIS LIBRARY G-50.1 .-2. T\ V A UNIVERSITY OF ILLINOIS Agricultural Experiment Station BULLETIN No. 194 A NEW LIMESTONE TESTER BY CYKIL G. HOPKINS URBANA, ILLINOIS, JANUARY, 1917 LIMESTONE TESTER (Weight, about 40 grams. Capacities below connecting tube, about 35 cc. and 50 cc. respectively) A NEW LIMESTONE TESTER BT CYRIL G. HOPKINS, CHIEF IN AGRONOMY AND CHEMISTRY Since the publication of Circular 185, describing a limestone tester, the writer has designed a more simple apparatus by means of which the purity of limestone can be quickly ascertained with a very satisfactory degree of accuracy. As shown in the accompanying illustration, this tester consists of two small glass bottles, joined together and fitted with ground-glass stoppers, the stopper of the smaller bottle resting upon a surface only slightly inclined from the horizontal, and projecting loosely into the neck. A set of weights from 5 milligrams to 50 grams, a balance suit- able for these weights with a capacity of 100 grams, a thermomeer, a 25 cubic centimeter graduated cylinder, and the limestone tester, are all one needs for testing limestone for relative purity. To make the test, place 5 grams of pulverized limestone in the larger bottle and fill the smaller one to the side-opening with acid made by mixing about equal parts of concentrated hydrochloric acid and water and saturating with carbon dioxid. Insert the stoppers and weigh. Now tip the apparatus carefully until the acid begins to flow thru the side-opening. As it drops upon the limestone, the carbonate is changed to chlorid and the liberated carbon dioxid gas passes thru the side-opening, lifting the small stopper as it passes out. Partly immerse the apparatus in cool water to keep it at about room tempera- ture. Gradually transfer the acid until foaming 1 ceases; then dry the apparatus with a soft cloth, weigh, and note the loss. To this loss in weight add .6 milligram for each cubic centimeter of air-space in the "loaded" apparatus, then deduct the proper percentage for the room temperature (about 1 percent for 70 F. see Table 1), and divide by 2.2 to get the relative purity of the stone. If the direct loss represented only the total carbon dioxid liber- ated, then its weight divided by 2.2 would give the relative purity of the stone in terms of calcium carbonate, since 5 grams of pure calcium carbonate (CaC0 3 ) contains 2.2 grams of carbon dioxid (C0 2 ), the atomic weights being 40 for calcium, 12 for carbon, and 16 for oxygen. However, the moist air which fills the air-space at the beginning is replaced by moist carbon dioxid during the reaction. At 70 Fah- renheit (21 centigrade) and 29.33 inches (745 millimeters) barometric 'Too persistent frothing may be prevented by adding a few drops of gas- engine cylinder oil to the acid before weighing the "loaded" apparatus. 487 488 BULLETIN No. 194 [January, pressure (taken as room temperature and average atmospheric pres- sure at an elevation of 600 feet above sea level), 1 cubic centimeter contains 1.744 milligrams of carbon dioxid or 1.148 milligrams of air, not including the water vapor. The difference in weight is practically .6 milligram per cubic centimeter; and, if the air-space in the "loaded" apparatus is, for example, 75 cubic centimeters, then 45 milligrams should be added to the loss in weight, under these condi- tions. Again, the gas (air or carbon dioxid) passing out of the appa- ratus during the reaction is accompanied by some water vapor, which amounts to .018 milligram per cubic centimeter at 70 F. The com- bined weight of the carbon dioxid and water vapor in 1 cubic centi- meter, at 70 F. and 29.33 inches, is 1.762 milligrams (1.744 + .018). Thus, about 1 percent must be deducted from the first corrected weight. For example, 5 grams of a certain limestone shows a loss of 1.990 grams. The first correction (45 milligrams) increases this to 2.035 grams, and the second correction (20 milligrams) reduces it to 2.015 grams. This divided by 2.2 gives .916, or 91.6 percent, as the relative purity of the stone. For all practical purposes, the first correction is a constant for each apparatus, the variations for ordinary differences in temperature and pressure being negligible. The second correction varies appre- ciably only with change of temperature. For each 2 degrees above 70, the correction of 1 percent is increased by about .1 percent. Thus, if the room temperature is 86, add to the weight of escaped gas .6 milligram per cubic centimeter of air-space and then deduct 1.74 per- cent (see Table 1). This, in the above example, with a direct loss of 1.900 grams, would give a final corrected weight of 2.000 grams of carbon dioxid from 5 grams of stone, and this divided by 2.2 gives 90.9 percent. But to perform the operation at 86 and figure the sec- ond correction at 1 percent, as should be done for 70, would intro- duce an error of .7 percent in the purity found. To saturate the hydrochloric acid with carbon dioxid, drop a piece of limestone weighing 3 or 4 grams into a pint bottle of the diluted acid, replacing the stopper after foaming ceases. To determine the air-space in the "loaded" apparatus, place 5 grams of pulverized limestone in the larger bottle, fill the smaller bottle to the side-opening with water, and then pour in measured water from a graduated cylinder and note the addition .required to completely fill the apparatus. If one has a barometer, and a balance capable of weighing to 1 milligram, a still higher degree of accuracy may be secured by using the data given in the accompanying tables. Thus, 5 grams of pulverized limestone shows a direct loss of 2.164 grams at 77 and 28.50 inches, with an apparatus having 71 cubic centimeters air-space when "loaded." When saturated with water 1917] 489 TABLE 1. CARBON DIOXID SATURATED WITH WATER VAPOR AT 760 MILLIMETERS (29.92 INCHES) Temperature Milligrams per cubic centimeter Percent of water in total Pressure of water vapor millimeters C F Carbon dioxid Water vapor Total 10 50.0 1.879 .009 1.888 .50 9.2 11 51.8 1.870 .010 1.880 .53 9.8 12 53.6 1.862 .011 1.872 .57 10.5 13 55.4 1.853 ..Oil 1.864 .61 11.2 14 57.2 1.844 .012 1.856 .65 11.9 15 59.0 1.836 .013 1.848 .69 12.7 16 60.8 1.827 .013 1.840 .73 13.5 17 62.6 1.818 .014 1.832 .78 14.4 18 64.4 1.809 .015 1.824 .83 15.4 19 6G.2 1.800 .016 1.816 .89 16.3 20 68.0 1.791 .017 1.808 .95 17.4 21 69.8 1.782 .018 1.800 1.01 18.5 22 71.6 1.773 .019 1.792 1.08 19.7 23 73.4 1.763 .020 1.784 1.15 20.9 24 75.2 1.754 .022 1.773 1.22 22.2 25 77.0 1.744 .023 1.767 1.29 23.6 26 78.8 1.735 .024 1.759 1.37 25.0 27 80.6 1.725 .026 1.751 1.46 26.5 28 82.4 1.715 .027 1.742 1.55 28.1 29 84.2 1.705 .029 1.734 1.64 29.8 30 86.0 1.695 .030 1.725 1.74 31.5 31 87.8 1.685 .032 1.716 1.85 33.4 32 89.6 1.674 .033 1.707 1.96 35.4 33 91.4 1,664 .035 1.609 2.08 37.4 34 93.2 1.653 .037 1.690 2.20 39.6 35 95.0 1.643 .039 1.682 2.34 41.8 vapor under those conditions, 1 cubic centimeter contains 1.659 milli- grams of carbon dioxid or 1.093 milligrams of air, the difference being .566 milligrams, or 40 milligrams in 71 cubic centimeters. This first correction being added gives 2.204 grams of moist carbon dioxid, of which 1.29 percent, or 28 milligrams, is water vapor, leaving 2.176 milligrams of dry carbon dioxid, and this divided by 2.2 gives 98.9 percent; whereas, if the barometric pressure were assumed to be 29.33 inches, the purity found would be 99.0 percent, as may readily be computed from the data given in Tables 1, 2, and 3. NOTE. This method of testing for relative strength or purity serves to meas- ure the basicity (power to neutralize acidity) of dolomitic as well as of the more common limestone, but to hasten the reaction it is well to pulverize dolomite so it will pass thru a 100-mesh sieve. 490 BULLETIN No. 194 [January, ', o oq to * ca o 00 > * w o . 'P, * ^ oi >-H co in m m m m in in co co co co co to b- b- b- b- b-oocooooo oo co o o o <3i O CXJ CO in CO CO OS O r-l - m ro eo po po pri pr^ p^ ?(~! 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