December, '11] COLEMAN: hydrocyanic acid gas 529 



For control of the gas production the following table, constructed 

 from the results of a large number of experiments, can be depended 

 upon to give very satisfactory results in production of the low per- 

 centages of gas required in the work. 



1 Litre of Hydrogen =0.0896 gram 



1 Litre of HON = .0896X9.006 (At. wt. HON) = .8069 gram 



1 ec. AgNOa N/10= .00054 gram HON. 1 cc. AgNOa N/100= .000054 gram HON 



5 grams KCN (98-99'^ ) in 500 ee. HjO (distilled) at 15° C. 



The amount of gas produced by the addition of the given quantity 

 of acid will vary slightly at different temperatures. The quantities 

 noted being for an average of 15°C. It will require slightly less at 

 higher temperature and more at lower temperatures. 



A centigrade thermometer is inserted through one hole in the cork 

 in one neck of the Woulff bottle into the liquid and a record made of 

 the temperatures throughout each experiment. 



For measuring the acid a 25 cc. pipette graduated to 0.1 cc. and fitted 

 with rubber tube and pinch cock for controlling the flow, mounted 

 in a holder, is very satisfactory. 



In order to ehminate all chance of leakage, or contamination of gas, 

 a Novy's gas-jar (Plate 21) is used for treating large numbers of 

 scale insects at one time. While for treating scale or other insects 

 in series, a series of vials, each five inches in length, with two hole 

 rubber corks through which glass tubing is passed, one tube reach- 

 ing well down to the bottom of vial, the other just through the cork 

 and the vials are connected in series as desired by rubber tubing 

 (Plate 22). 



One end of this series of vials is connected with the gas-generating 

 bottle by rubber tubing. A calcium chloride tube being inserted if 

 it is desired to use dry gas. The other end of the series is connected 

 with a gas wash bottle of 250 cc. capacity in which is placed 200 cc. of 

 N./lOO solution of potassium hydrate (KOH). This flask is connected 



