the Action of Water on White Precipitate. 429 



of potassium, there is ammonia disengaged, and a brown 

 powder formed. To this reaction I shall hereafter recur. In 

 order to determine the composition of this yellow powder, 

 the following experiments were made : — 



A. — 100 parts of corrosive sublimate were dissolved in 

 water, and ammonia added in excess. The mass, in place of 

 being filtered cold, was boiled until the light-white precipitate 

 was changed into the clear yellow heavy powder ; it was then 

 filtered, and the quantity of product determined. The liquor 

 and washings were acidulated by nitric acid, and precipitated 

 by nitrate of silver, and the chloride abstracted from the sub- 

 limate thus determined ; the liquor contained a very small 

 trace of mercury. Several experiments were made on this 

 plan, the results of which are exhibited in the following table : 



100 parts of sublimate gave, 



Exp. Yellow powder. Chlorine in liquor. 



1 83-5 19*25 



2 83-3 18*50 



3 84-7 18-90 



mean 83*83 18-89. 



Now 100 of sublimate contain 



Mercury 74'09 



Chlorine 25*91. 



Hence we see that there have been abstracted from the 

 sublimate three-fourths of Us chlorine ; the remaining fourth, 

 and all the mercury, existing in the yellow powder. We have 

 therefore in 83*83 parts of it : 



Mercury 74*09 



Chlorine 71*02 



Or in one hundred parts, 



Mercury 88-381 



Chlorine 8*374 



B. — When white precipitate already prepared is boiled with 

 water, there is obtained a similar yellow powder, and the su- 

 pernatant liquor is found to contain only sal-ammoniac. As 

 we know, within very strict limits, the composition of the 

 white powder, we can make use of this reaction to illustrate 

 the nature of the yellow product: 



100 parts of white precipitate were boiled with water until 

 completely converted into the yellow powder; the liquor, 

 which was quite neutral, was acidulated ; and the chlorine dis- 

 solved precipitated as chloride of silver, from which its quan- 

 tity was obtained by calculation. The following table gives 

 the results of experiments conducted in this manner : 

 100 of white precipitate gave 



