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F. J. BRIXLEY AND R. H. BAKER. 



(a). The humidifying unit is filled with either distilled water or 

 various strengths of sulfuric acid to give the desired humidity. 

 The air, after passing through the flow regulator, passes over the 

 humidifying unit and through the first flow meter, which gives 



FIG. i. Apparatus used in determining the toxicity of HCN to insects. 



the total rate of flow in liters per hour. The air line is divided 

 after leaving flow meter No. i ; part of the air passes directly 

 into the gassing chamber E, the remainder of the air goes through 

 the second flow meter, thence to the generating flask D, which 

 contains the source of HCN (calcium cyanide or liquid HCN). 

 The air saturated with HCN mixes with the pure air in the tube 

 leading to the gassing chamber E. The apparatus is so designed 

 that the concentration of HCN can be regulated by controlling 

 the amount of air which passes through the second flow meter. 

 The reading of the second meter gives the rate of flow of air 

 through the generating flask. The air-gas mixture, after leaving 

 the gassing chamber, passes into the absorption bottle G con- 

 taining a concentrated solution of NaOH for the purpose of 

 absorbing the HCN, thus preventing any escape of the gas into 

 the room. 



To collect a sample of gas for analysis, the gas-air mixture 

 is passed through a small absorption bottle F by turning a two- 

 way stopcock /. In this work two methods of analysis were 

 used. The first method consists of collecting one liter of gas 

 in a 10 per cent. NaOH solution and titrating with silver nitrate. 



