A tared filter paper is placed in a funnel to the neck of which has been fitted a piece of rubber tubing provided with a clip. The paper is moistened with a solution of acetone and ammonia, the cap composition is weighed off directly on to the filter paper and is then covered with the solution of acetone and ammonia and allowed to stand thirty-four hours. It is then washed repeatedly with the same solution until the washings give no coloration with ammonium sulphide, and afterwards washed with acetone until washings give no residue on evaporation dried and weighed. The paper is again put in the funnel and washed with water until free from potassium chlorate, dried and weighed.
If c = weight of composition taken,
d = " " filter paper,
a = " after first extraction,
b = " " second extraction,
then c+d-a = weight of fulminate,
c+d-a-b = " " KClO_{3},
b-d = " " sulphide of antimony.
The composition should be finely ground in an agate mortar.
The results of the analysis by this method of two mixtures of known composition are given below—
________________________________________________________________________ | | | | | | A | B | | | | | | | Percentage | Percentage | Percentage | Percentage | | | Taken. | Found. | Taken. | Found. | |____________________|____________|____________|____________|____________| | | | | | | | Antimony Sulphide | 36.47 | 36.25 | 37.34 | 37.22 | | Potassium Chlorate | 33.25 | 33.71 | 46.03 | 46.43 | | Mercury Fulminate | 30.27 | 30.02 | 16.61 | 16.34 | |____________________|____________|____________|____________|____________|
Dr. H.W. Brownsdon's (Jour. Soc. Chem. Ind., xxiv., April 1905) process is as follows:—The cap composition is removed by squeezing the cap with pliers, while held over a porcelain basin of about 200 c.c. capacity, and removing the loosened foil and broken composition by means of a pointed wooden chip. Composition adhering to the shell or foil is loosened by alcohol, and washed into the dish by means of alcohol in a small wash bottle. The shell and foil are put to one side and subsequently weighed when dry. The composition in the dish is broken down quite fine with a flat-headed glass rod, and the alcohol evaporated on the water bath till the residue is moist, but not quite dry, 25 c.c. of water are then added, and the composition well stirred from the bottom. After the addition of 0.5 grm. of pure sodium, thiosulphate, the contents of the dish, is well stirred for two and a half minutes. One drop of methyl orange is then added, and the solution titrated with N/20 sulphuric acid, which has been standardised against weighings of 0.05-0.1 grm. fulminate to which 25 c.c. of water is added in a porcelain dish, then 0.5 grm. of thiosulphate, and after stirring for two and a half minutes, titrated with N/20 sulphuric acid. The small amount of antimony sulphide present does not interfere with the recognition of the end point. After titration, the solution is filtered through a small 5-1/2 cm. filter paper, which retains the antimony sulphide. The filter paper containing the Sb_{2}S_{3} is well washed and then transferred to a large 6 by 1 test tube. Five c.c. of strong hydrochloric acid are added, and the contents of the tube boiled gently for a few seconds until the sulphide is dissolved and all the H_{2}S driven off or decomposed: 2-3 c.c. of a saturated solution of tartaric acid are added, and the contents of the tube washed into a 250 c.c. Erlenmeyer flask. The solution is then nearly neutralised with sodium carbonate, excess of bi-carbonate added, and after the addition of some starch solution titrated with N/20 iodine solution. This method for small quantities of stibnite is both quick and accurate, the error being about ±0.0003 grm. Sb_{2}S_{3} at the outside.
The tendency of this method is to give slightly low figures for the fulminate, but since these are uniform within a negligible error, it does not affect the value of the results as a criterion of uniformity. The following test results were obtained by Dr Brownsdon:—
____________________________________________________________ | | | | | Fulminate Taken. | Fulminate Found. | Error. | | Grm. | Grm. | Grm. | | | | | | 0.0086 | 0.0083 | -0.0003 | | 0.0082 | 0.0081 | -0.0001 | | 0.0074 | 0.0071 | -0.0003 | | 0.0068 | 0.0066 | -0.0002 | |____________________|___________________|___________________| | | | | | Stibnite Taken. |Sb_{2}S_{3}, Found.| Error. | | Grm. | Grm. | Grm. | | | | | | 0.0085 | 0.0084 | -0.0001 | | 0.0098 | 0.0099 | +0.0001 | | 0.0160 | 0.0157 | -0.0003 | | 0.0099 | 0.0100 | +0.0001 | |____________________|___________________|___________________|
TABLE FOR CORRECTION OF VOLUMES OF GASES FOR TEMPERATURE, GIVING THE DIVISOR FOR THE FORMULA.
V_{1} = V x B/(760 x (1 + dt)) (d = 0.003665) 1 + dt from 0° to 30° C.