T H E J O C R N A L O F I A T D U S T R I A L A N D E N G I -VE E RI N G CH E M I S T R Y
Apr., 1916
complete reduction of XSV t o Asiii in hydrochloric acid solution, and t h a t in those cases in which satisfactory results have been obtained b y t h e distillation method, using ferrous salts as reductors, one or more of t h e following conditions obtained: ( a ) metallic copper or a salt of copper was present, in which case some cuprous chloride would be formed; ( b ) t h e arsenic was present in very small a m o u n t ; (c) t h e arsenic was present as metallic arsenic or as a n arsenite and not as a n arsenate. 11-Cuprous chloride effectively reduces AsV t o A\siii in hydrochloric acid solution, and t h e arsenic trichloride is completely separated from antimony, lead, copper, zinc, iron and calcium b y distillation. IKSECTICIDE A N D FUKGICIDE LABORATORY BUREAUOF CHEMISTRY, TVASHIKGTOX
A SIMPLE AND RAPID ASSAY OF LEAD B y GRBGORY TOROSSIAN Received November 13, 1915
The following simple and rapid method for t h e approximate quantitative determination of lead may be of value t o metallurgists, mining engineers, prospectors and others who have occasion t o estimate quickly and with reasonable accuracy t h e lead cont e n t of certain lead compounds and minerals. T h e method is based upon the reduction of lead compounds by nascent hydrogen and is carried out TABLE I SAXPLE pbo.,,. , , , ,,.,,,.,,
Gram taken
o.iono 0.1000 0.1290 0.1858 0.1308 0. 1155
0 1167
PbSOA.. . . . . . . . . . . . 0 . 1 8 9 0 0.1435 0,1190 0.1774 0.1875 Pb(CzH30a)~.3HzO... . 0 , 2 0 1 0 0.1009 0,1028 0.1190
0,1150 0.1100 0.1056 0.1000 0.1092 PbC03. . . . . . . . . . . . . 0.1695 0.1720
O.li65
Red l e a d . . .
.......
0.1910 0.2090 0.1915 0.1740
Red l e a d . . . . . . . . . . . . . . . . .
TheoP h FOVXD Average retical Gram Per cent P e r cent Per cent 0.0925 ~2.50 0.0928 9 2 . 8 0 ’I 0,1196 92.72 0.1713 92.20 1 92.62 92.83 0.1215 92.89 0 . 12.50 92.25 0 1085 92.97 J 0.1310 69.31 1 0.1000 69.69 0.0830 69.75 69.32 68.31 0.1225 69.05 0.1290 68.80 0.1090 54.72 0.0552 5 4 . 7 1 0.0568 55.26 0.065i 55.20 0,0635 55.22 0.0596 54.19 0.0585 0.0552 0.0597 0 1305 76.99 0.1325 77.04 1 0.1370 77.80 1/.32 i7.54 0.1480 ii.48 0.1920 91.87 ‘ 0,1745 91.12> .,. ... 0.1590 91.38) ..... YO.79 (Regular analysis, 90.17)
j
5% 1 1i \ __ i
as follows: A n aluminum plate 2 in. wide, j in. long and about 0 . 0 3 in. thick is used. d b o u t l / d in. from each end of the plate concave cups are formed b y placing t h e plate over one of the t h u m b holes of a crucible tong or over a suitable ring and striking it with a pestle. The diameter of the cup need not be more t h a n an inch and t h e depth about 3 / 1 ~in. Before using, the aluminum plate is rubbed with emery paper or sand so as t o clean the surface from the aiuminum oxide coating t h a t hinders t h e action of acids. Each cup will serve for about fifteen determinations. From 0 .I j t o 0 .z g. of the finely powdered sample is placed in the cup on the aluminum plate (it
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may b e weighed directly on t h e plate in t h e cup) and moistened with a drop or t w o of dilute ( I : 3) hydrochloric acid. More acid is added, drop b y drop, until the, action of t h e acid on the aluminum is \vel1 started. T h e sample is subjected t o this treatment for several‘seconds or until the original color of t h e sample almost disappears or is changed markedly. By this time the sample becomes spongy, may he turned over by a pointed glass rod or gently stirred and more acid is added drop b y drop, if necessary. After a minute or two t h e contents of the cup are stirred with a pointed glass rod for about j min. or until all indications point t o the completion of t h e reaction. I n t h e case of PbS the fact t h a t H2S is no longer evolved is a good indication for the end of reaction. With colored lead compounds the disappearance of the color is indicative t h a t the reduction is over. I n the author’s experiments the reductions took from 5 t o I O min. When the reduction is over, a little pure water is added t o the cup and after gentle stirring the liquor from the cup is decanted; this operation is repeated 4 or j times, or until t h e wash mater shows no acid reaction (litmus test or “tongue t o u c h ” ) . Now the spongy metallic lead in t h e cup is pressed together with a glass rod so as t o make it solid and compact, then a filter paper is ‘pressed over the lead t o dry it as completely as possible. Finally, one drop of water is placed near the cup on the plate which is now warmed above a small flame or a lighted match or a n y convenient small source of heat until the mater is evaporated; this also dries the lead metal in the cup. The dried lead is now detached from t h e plate by a pocket knife and weighed, and the percentage of lead is calculated on t h e original sample. This method is very simple and quick and sufficiently accurate t o be of value in many instances of rapid estimation of lead in minerals and compounds. The d a t a in Table I show the degree of accuracy attained in this method. C. P. products were used for the experiments. NATIONAL CARBON COMPANY. CLEVELASD
T H E ANALYSIS OF MAPLE PRODUCTS, VI1 T h e Electrical Conductivity Test for Purity of Maple Syrdp B y J. F. SNBLL Received -4ugust 20, 1915 CORRECTIOXS TO PAPER I ’
In Paper I of this series, describing an electrical conductivity test for the purity of maple syrup, published in THISJOURSAL, 5 (1913), 740, the following corrections should be noted:? P. 745, Table TI,Column 8 (i.e . , fourth column from the right) : The minimum value of “ B I D ” is 83 and the per cent deviation of the minimum from the mean is, therefore, 2 9 , I per cent instead of 2 1 . 4 . Column I O (next t o last): The heading should be “ F I G ” instead of “E,’G.” Last column: The decimal point has been omitted from all but two of the ratios. Before each of these insert “ 0 . ” 1 Presented a t t h e 5 1st Meeting of t h e -4merican Chemical Society, Seattle, August 31 t o September 2 , 1915. 2 I n t h e edition of Paper I, published in Trans. R o y . SOC.(Canada), 131 7 (1913), 165-182. these errors were corrected.
