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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
tures or for control of rate of gas flow, as, for example, chlorination of natural gas and the determination of the heating value of gases. Acknowiedgment ;s made to the Gas Laboratory of the Pittsburgh Experiment Station of t h e Bureau of Mines for the pioneer work in applying flow meters t o
Vol.
11,
No. 4
measuring the rate of gas flow and the application of this principle t o testing gas mask absorbents and gas masks.
*.
GAS MASK RESEARCH DIvrsroN, c. w. s,, u. s. AMERICAN UNIVERSITY EXPBRIMENT STATION WASHINGTON, D. C.
ORIGINAL PAPERS THE GRAVIMETRIC AND VOLUMETRIC DETERMINATION OF MERCURY PRECIPITATED AS MERCURY ZINC THIOCYANATE1 B y GEORGE S. JAMIESON Received July 22, 1918
*
The methods t o be described are based upon t h e precipitation of t h e .mercury from mercuric compounds in neutral or acid solutions with a reagent which contained 39 g. of ammonium thiocyanate and zg g. of zinc sulfate per liter. T h e precipitate of mercury zinc thiocyanate was either weighed or titrated with a standard solution of potassium iodate in t h e presence of strong hydrochloric acid and an immiscible solvent such as chloroform in the same manner as recently described for the determination of zinc.2 I n order to get a quantitative precipitation of t h e mercury zinc thiocyanate there should not be more than 5 per cent of acid present in t h e solution before the addition of the precipitating reagent. Also i t should be observed t h a t in cases where larger quantities of acid are required for t h e solution of a substance the excess of acid should be neutralized with sodium hydroxide instead of ammonia because an excessive amount of ammonium salts exerts a solvent action upon the precipitate of the double thiocyanate. It was found t h a t cobalt, copper, bismuth, and nickel were partially precipitated along with the mercury zinc thiocyanate, and consequently, if present, they would interfere with the determination of t h e mercury. The volumetric procedure has been applied t o the determination of mercury in various kinds of antiseptic tablets and several other mercuric preparations with satisfactory results which are given below. I n order t o test the gravimetric method several solutions of mercuric chloride were * prepared and standardized by the well-known sulfide method. Measured volumes of these solutions were taken in perfectly clean, small beakers. Each solution was treated with 2 5 cc. of the reagent and diluted so t h a t the final volume would be about 7 j cc. The solutions were vibrated by striking t h e sides of the beakers with a stirring rod t o facilitate the separation of the crystals. After the solutions had stood for about j min. they were briskly stirred with a glass rod, previously moistened with water, for about a minute. This treatment permitted the rod t o be easily rinsed free from t h e precipitate so t h a t it could be removed from t h e beaker. The solutions were allowed t o stand a n hour or longer before filtration. The precipitates were collected on Gooch crucibles and washed four or five times with a washing solution which contained 5 cc. 1
Published by permission of the Secretary of Agriculture.
2
J A m . Chem. Soc., 40 (1918), 1036.
of t h e thiocyanate reagent a n d 450 cc. of water, on account of t h e solubility of t h e mercury zinc thiocyanate in pure water. T h e crucibles containing t h e precipitate were dried for a n hour between 1 0 2 ' a n d 108' C. a n d weighed. The mercury was calculated by multiplying t h e weight of the precipitate by t h e factor 0.40258. T h e dried double thiocyanate has the composition HgZn(SCN)4. The following results were obtained: No.
........
H g Taken
Gram
HgZn(SCN)'a Gram
0.0402 0.1239 0.1328 0.1118 0.1451 0.1209 . O . 1360 0,0907
0.1006 0.3082 0.3305 0.2783 0.3605 0.3009 0.3385 0.2246
I.. 2. . . . . . . . . . 3.......... 4
.......... S...... . . . . 6 .......... 7 . . ......... 8 ..........
Hg Calculated Gram 0.0405 0.1240 0.1327 0.1120 0.1451 0.1211 0.1362 0.0904
Error
Gram -~ +0.0003 ~~
+O.OOOl -0.000 1 $0.0002 0.0000 +0.0002 +o .0002 -0,0003
I n Analysis 8, t h e precipitate was allowed t o s t a n d for only half an hour instead of a n hour or longer as recommended above. The test analyses show t h a t satisfactory results can be obtained by this method. I n order t o test the volumetric method for the determination of mercury when precipitated as t h e double thiocyanate, two solutions of potassium iodate were used. The first one which had been made for another purpose, contained 39.2882 g. of KIOa in 1000 cc., a n d t h e second one, specially prepared for this investigation, contained 19.2191 g. of KIOs in 1000 cc. According t o t h e equation
+ 6KI03 + I z H C l = HgS04 + ZnSOl + + 4 H C N + 61C1 + 6KC1 + 2HzO
HgZn(ScN)e ~HzS04
the first solution will have I cc. equivalent t o 0.006133 g. of Hg a n d the second solution will have the value I cc. = 0.00300 g. of Hg. Measured volumes of t h e standard mercuric chloride solutions mentioned above were precipitated and allowed t o stand as previously described. The solutions were filtered on 7 cm. washed filters, using gentle suction. The precipitate adhering t o t h e beaker was transferred t o t h e filter by means of a small wash bottle containing I O cc. of t h e thiocyanate reagent and 4 j o cc. of water. Then t h e filters were washed around t h e upper edge four times with small quantities of the washing solution. When the filters had drained, t h e suction was stopped. The filters were carefully removed from t h e funnels and were folded so t h a t they could be placed in 8 oz. glass stoppered titration bottles. A thoroughly cooled mixture of 3 5 cc. of concentrated hydrochloric acid and I O cc. of water along with 7 cc. of chloroform was added t o one of t h e titration bottles containing mercury zinc thiocyanate, because it is best t o titrate immediately after adding t h e acid t o t h e precipitate. During t h e first p a r t of t h e titration the potassium
T H E J O U R N A L O F I N D L ' S T R I A L A N D E,VGliVEERING C H E M I S T R Y
-Apr., 1919
iodate is added rapidly while rotating t h e bottle in order t o keep t h e contents mixed. When the iodine; which is liberated during t h e first stage of t h e reaction, has disappeared from t h e solution, t h e stopper is inserted and t h e contents of t h e bottle are thoroughly mixed by shaking for about half a minute. From this point the titration is continued slowly, shaking t h e closed bottle thoroughly after each addition of potassium iodate solution, until the iodine color has disappeared from t h e chloroform indicator which marks the end-point. If more t h a n 60 cc. of t h e potassium iodate solution are required, I O t o I j cc. more of concentrated hydrochloric acid are added before proceeding with the titration. The following results were obtained : KIOa Re- Hg Calculated quired. Cc. Gram 16.40 0.1006 0.0806 13.15 8.25 0.0506 0.0806 13.15 14.70 0.0902 3.30 0.0202 0.0825 13.45 15.40 0.0945 13.15 0.0806 35.15 0.1055 0.1206 40.20 0.0905 30.15
Hg Taken Gram .0.1006 0.0805 0.0503 0.0805
&TO.
I.. ........ 2 . . .. . . . . . . 3.. . . . . . . . . -4. . . . . . . . . .
8... .
.....
0.0945
1 1 . . . . . . . . . . 0.1209 12.. . . . . . . . . 0,0907
Error Gram 0.0000 +O.OOOl +0.0003
+O,OOOl
-0,0003 +o 0001 0.0000 0.0000 +O,OOOl -0.0002 -0,0003 -0.0002
.
Analyses I O t o 1 2 were made with t h e second potassium iodate solution mentioned above with I cc. = 0.00300 g. of Hg. T h e test analyses show t h a t t h e method gives satisfactory results providing t h a t t h e directions given above are closely followed. This method was further tested b y employing it for t h e determination of mercdry in a sample of yellow mercuric oxide which had been analyzed b y the sulfide method. Weighed portions of t h e oxide were dissolved in 2 cc. of I : I nitric acid and t h e resulting solutions were diluted with 3 5 t o 40 cc. of water and precipitated in the usual manner. T h e following results were obtained: h'O.
1 .
2
.
..
HgO Taken Gram 0.1828 0.2215
,
Cc. K I O 2 Reouired 56.40 68.30
Hg Found Per cent 92.56 92.57
Hg by Sulfide Method Per cent 92.56 92 63
I n applying t h e method t o the analysis of antiseptic tablets, a sample was prepared b y grinding a dozen of t h e tablets t o a fine powder. The portions taken for analysis were dissolved in 3 5 t o 40 cc. of water and three drops of hydrochloric acid were added before the mercury was precipitated. I n the case of t h e mercuric cyanide tablets which contained borax it was necessary t o add I cc. of hydrochloric acid. T h e following results were obtained: H g by HgCh Sulfide Found Method PREPARATION Per cent Per cent 47.96 47.97 HgC12, NH4Cl.. . . . . . . . . . . . . . . . . 47.97 48.00 46.49 46.50 Green HgClz, NH4C1 ............ 46.51 46.44 63.49 63.64 Blue HgCh, citric a c i d . . 63.59 63.51 Hg(CN)z Hg(CN)a 20.15 35.62 35.67 Pink Hg(CN)2, b o r a x . . . . . . . . . . . 0.2137 0.3054 28.85 35.69 35.76 1 cc. of KIOa soln. = 0.003000 g. of Hg, 0.004060 g. of HgC12, o r 0.003778 g. of Hg(CN)z. Sample Taken Gram 0.2358 0.3623 0.3428 0.3313 0.2024 0.2551
i
........ I
KIOa Required Cc. 27.85 42.80 39.25 37.95 39.25 39.95
t
I n t h e case of t h e green tablets, some of t h e dye was precipitated with t h e mercury zinc thiocyanate a n d consequently a light green color was imparted t o t h e
297
chloroform indicator. However, by watching t h e color change in t h e chloroform, t h e end-point of t h e titration was easily seen. I n order t o dissolve basic mercuric salicylate it was found necessary t o heat the portions taken for analysis with 2 t o 3 cc. of I : I nitric acid in covered beakers. When all was in solution, 40 cc. of water were added and the mercury was precipitated as soon as the solution had cooled t o room temperature. KI03
Sample Taken Gram 1. . . . . . . . . . . . . 0.2040 2 . . . . . . . . . . . . . 0.2006 3 . . . . . . . . . . . . . 0.1876
NO.
Required cc. 38.30 37.60 35.15
Hg Found Per cent 56.32 56.23 56.21
Hg by Sulfide Method Per cent 56.31 56.30
...
Ammoniated mercuric chloride (HgClN Hz) was best dissolved by treating t h e portions taken for analysis with 5 cc. of concentrated hydrochloric acid. The mixture was allowed t o stand for about half a n hour with frequent shaking; then it was diluted with 5 cc. of water and heated just long enough t o dissolve all of t h e substance. Immediately 40 cc. of cold water were added, and when the solution was cold t h e mercury was precipitated as described above. The following results were obtained: Sample Taken Gram I . . . . . . . . . . . . . 0.1709 2 . . . . . . . . . . . . . 0.1896 3 . . . . . . . . . . . . . 0.1757
NO.
KIOa
Required cc. 45.50 50.50 46.70
Hg Found Per cent 79.87 79.91 79.79
Hg by Sulfide Method Per cent 79.86 79.86
...
The tables of analyses given above show t h a t t h e iodate method gives very satisfactory results when applied t o the analysis of antiseptic preparations. However, it should be observed t h a t in order t o get satisfactory results, it is essential t h a t t h e directions given above should be closely followed in every particular. Mercurous compounds can be titrated directly by the iodate method which has been previously described.l BUREAUO F CHEMISTRY DEPARTMENT OF AGRICULTURE WASHINGTON, D. C.
COLORIMETRIC DETERMINATION OF ORGANIC SUBSTANCES By H. HEIDENHAIN Received August 26, 1918
Many years ago I published a method for t h e volumetric determination of organic substances2 which was based on the observations t h a t a mixture of a dilute solution of potassium bichromate and sulfuric acid in certain proportions could be boiled for a long time with hardly any decomposition of t h e chromic acid and t h a t a large number of organic compounds could be oxidized by such mixture either quantitatively or nearly so. According t o t h e quantity of t h e organic substance present t h e reaction produced solutions of different shades of color ranging from a pure green, indicating complete reduction of t h e chromic acid, t o t h e pure orange of t h e undecomposed chromic acid with all shades of yellowish green and greenish yellow between these extremes. It occurred t o me t h a t here was a n opportunity t o develop a colorimetric method for t h e determination 1
a
A m . J . Sci., 33 (1912), 349. J . Am. Chem. Soc., 15 (1893), 71.
