CHEMISTRY OF FUMIGATION". 



101 



of the cyanid, previously dissolved in 10 cc of water, and partially 

 open the stopcock, allowing the solution of the cvanid to flow slowly 

 into the acid. As soon as the stream of hydrocyanic-acid gas reaches 

 "B," containing the potassium hydrate, it is absorbed very readily; 

 in fact, so readily that unless the flow is quite rapid the potassium- 

 hydrate solution rises in the tube and in several instances was drawn 

 back into flask "A." In order to prevent this it is necessary to watch 

 the apparatus constantly and not permit the flow of gas to subside; 

 or, if this is impossible, to close the pinchcock on the tube connecting 

 the two flasks for an instant and apply suction. As soon as the solu- 

 tion of the cyanid has all been added the separatory funnel is washed 

 down with 1 cc of water, heat is applied to flask "A," and the tem- 

 perature of the acid brought to 110° C, which is about the average 

 temperature obtained by adding 1 part acid to 2 parts water. The 

 heat is then removed, flask U F" attached, suction applied, and air 

 drawn through the apparatus for about 40 minutes. According to 

 the authorities, air alone drawn through a solution of a cyanid 

 causes it to decompose, but this action is very slow and for this work 

 can be neglected. The residue in U A" is washed out into a beaker, 

 cooled, made alkaline with potassium hydrate, and the amount of 

 cyanid present determined by titration with tenth-normal silver 

 nitrate. The solution in "B " is washed out into a 500 cc flask, made 

 to the mark, and aliquot portions used for the determination of the 

 cyanid present. Solutions in "C" and "D" were also tested for 

 cyanid, but in only two or three instances was any present, as in most 

 cases it had all been absorbed in "B. " 



RESULTS OF EXPERIMENTS. 



The results of the experiments conducted as outlined, when employ- 

 ing pure chemicals, are given in the following table: 



Results of experimental work. 



Experiment No. — 



Equivalent 

 of HCN in 

 the sam- 

 ple. 



Per cent of 



total HCN 



evolved. 



Per cent of 



total HCN 



remaining 



in "A." 



Per cent of 

 total HCN 



decom- 

 posed (by 

 difference). 



1 



Per cent. 

 51.82 

 51.82 

 51.82 

 51.82 

 51.82 



94.81 

 94.40 

 93.77 

 96.90 

 96.28 



3.59 

 3.29 

 3.84 

 2.20 

 1.40 



1.60 



2 



2.31 



3 



2.39 



4 



90 



5 



2.32 







Average 



51.82 



95.23 



2.86 



1.91 



These results indicate that there is some variation in the amount 

 of hydrocyanic acid decomposed, but this would be expected from 

 the fact that the experiments are subject to slight variations in the 



