Chemistry of Acid-manufacture, 



375 



oxide, the variation being from 2*6 per cent, to 3'2 per cent. 

 As* 0^. It is difficult to imagine how this arsenic has been re- 

 tained in the coke, as it would have been expected that the 

 decomposition of the terchloride by the water in the towers 

 would have been complete. (See Table V.) 



Table V. 

 Coke from Condensing-towers. 



No. of analysis. 



Arsenic trioxide. 



1. 

 2. 

 3. 



per cent. 

 2641 

 3182 

 2-837 



8-()6() 



Mean 



2-886 





Air in flue from condensing-towers to chimney. — Not only is 

 the decomposition of the arsenic terchloride not completed in the 

 towers, but a considerable amount of arsenic (in what condition 

 I am not aware) escapes from the flue leading; from the conden- 

 sing-towers to the chimney of the works. The amount of air 

 passing through this flue was 31,722 cubic feet per hour; and 

 for each analysis 500 cubic feet were taken. The method em- 

 ployed for collecting the arsenic (trioxide ?) contained in the air 

 passing through this and the next mentioned flue was as fol- 

 lows : — The air was aspirated through three bottles containing 

 respectively H'^ 0, HCl, and AgNO^. The gas was allowed to 

 bubble very slowly through the solutions; the bottles containing 

 them were capable of holding 40 ounces, and were about half 

 filled. It was found in most cases (it might almost be said in 

 all) that the AgNO^ solution was unnecessary, the H^ and the 

 HCl absorbing all the arsenic which was in the air drawn through. 



As an average of twelve analyses, the following results were 

 obtained : — 



As^O^ As" 03 As^O^ 



per 1000 cubic feet. per hour. per da}^ 



0-158 grain. 5*012 grains. 120-282 grains. 



This amount may appear small ; but when we consider that 

 the 120 grains per day are from the chimney of one works only, 

 the question becomes rather a serious one when we take into 

 account the number of manufactories employed daily in throwing 

 this amount into the air even within a short distance of Man- 

 chester. (See Table VI.) 



