344 M. R. Schneider on the Volumetric 



be used in the dilution, and that the determinations must be 

 made as rapidly as possible. The transient red colour produced 

 on the addition of iodine to a sulphuretted hydrogen solution 

 containing starch, is only feeble when the solution is greatly 

 diluted; it rapidly disappears, and does not prevent the true 

 iodine reaction. 



The details of the process are as follows : — 



The sulphide of antimony which lias been precipitated by 

 sulphuretted hydrogen from a solution containing tartaric acid*, 

 is collected on a filter of Swedish paper and completely washed 

 out, the last washings being with hot water. 



The filter with the partially dried precipitate is carefully 

 removed from the funnel, and pressed into such a form that it 

 can be conveniently introduced into the neck of a small flask. 

 With a little practice this is effected without breaking the filter, 

 and without any loss ; it is of course easier when the precipitate 

 is quite dry, for then it occupies less room. 



In decomposing the sulphide of antimony and collecting the 

 sulphuretted hydrogen, an apparatus may be used similar to 

 that which Bun sen has described in his paper on iodometric de- 

 terminations. The size of the flask varies with the quantity of 

 sulphide of antimony : for quantities of 0*3 to 0*4 grm. SbS 3 , a 

 flask of 100 cubic centims. capacity is sufficient ; for 0*4 to 1 

 grm. SbS 3 , the capacity maybe 200 cubic centims. The bottom 

 of the flask must be circular, the neck sharply tapering off, long, 

 narrow, and cylindrical. The retort which serves as receiver 

 must have two large bulbous enlargements blown in the neck : 

 the bulb part of the retort must be filled with water freed from 

 air; and from 30 to 50 cubic centims. of caustic ammonia must 

 be added, according to the quantity of the sulphide of antimony. 



The sulphide of antimony is then introduced into the flask, 

 hydrochloric acid mixed with one-fifth its volume of water added 

 in excess, the gas delivery-tube affixed, and then the distillation 

 commenced. 



The liquid in the receiver must still be alkaline when the 

 distillation js complete. It is left in the retort until cold, and 

 is then placed in a measuring vessel and its volume made up to 

 a litre or to half a litre with boiled water, according to the 

 quantity of sulphuret of antimony taken. 



An aliquot part of this, one-fifth or one-tenth, is used for the 

 determination. It is poured into a beaker and diluted with its 

 own volume (or twice its volume) of water free from air ; a strip 



* The addition of tartaric acid is quite essential ; for the sulphide of an- 

 timony precipitated from a hydrochloric acid solution persistently retains 

 some chloride of antimony, which is not the case in the presence of tartaric 

 acid. 



