EXPERIMENT STATION BULLETINS. 567 



celain crucible, and the resulting globule of silver was weighed. For 

 every atom of silver in the fused filtrate a molecule of hydrocyanic 

 acid had been caught in the potassium hydrate flask at the beginning. 

 One-fourth the weight of the silver, therefore, gave the weight of the 

 hvdrocvanic acid and from this weight its volume in the measured 

 amount of air-mixture became known and consequently its percentage 

 also. By subtracting this percentage from the combined percentage 

 value of carbon dioxide and hydrocyanic acid already found, the value 

 of the carbon dioxide present was given. 



A source of error, which needed most attention in this method was 

 due to the fact that hydrocyanic acid decomposes rapidly, forming 

 certain solid bodies.* The percentage of acid-gas in the(V') volume 

 Avas certain, therefore, to be enough lower than in the (V) volume to 

 introduce a fatal error in the carbon dioxide estimation unless certain 

 precautions were observed. Experiments showed that in the case of 

 air containing 10.5% of hydrocyanic acid, the decrease in the acid 

 might be as high as 1.1% in 15 minutes. But the rate of decrease fell 

 rapidly as the percentage of the gas became lowered; so that in air 

 containing 2.5% hydrocyanic acid, the fall was only 0.16% in 30 

 minutes. The tests were carried out under the ordinary light condi- 

 tions of the laboratory. 



At the best, about 10 to 12 minutes were required between the(V) 

 and (V) measurements. Moreover, high percentages of the poison 

 gas were not necessary or useful in studying the effect of this gas upon 

 respiration, since 0.8% in the respired air was sufficient to render P. 

 cormitus motionless in 8 to 10 minutes. Even 0.01 of 1% rendered 

 strong specimens of the beetle partly helpless for a time. 



The hydrocyanic acid used in these experiments was made from pure 

 potassium cyanide and sulphuiric acid in a vei^y small cup which was 

 floated on the mercury within a gas container. 



After a good deal of preliminary practice a series of eight sets of 

 experiments were carried out by the above method using three or four 

 specimens of P. cormitus at a time. In two of these, the amounts of 

 the respiratory exchange were very small and approached the limit of 

 accuracy so closely as to make the quotients found of doubtful value,: 



CO2 0.15 



e. g. — — = —- - • The other experiments, however, seemed to demon- 



° O2 O.IG '■ ' ' 



strate that the influence of hydrocyanic acid (when present in amounts 

 just sufficient to render the beetles helpless) was to increase, slightly, 

 the value of the respiratory quotient. Most of the quotients influenced 

 by this insecticide were only a little higher than those given by the 

 same insects in air; the average was 0.3 higher. The largest quotient 

 was -~~= 1.28 the quotient in air for the same specimens being 



1.08 ■^^ O.by. 



CO 

 EFFECT OF CARBON-DISULPHIDE VAPOR UPON ^ " OF PASSALUS CORNUTUS. 



A plan was worked out (in theory) for estimating the vapor of 

 carbon disulphide, Avhen present in air, by the combustion method — 

 the two products of complete combustion could both be estimated 



*A wliite cryst. powder was deposited in considerable amounts — probably ammonium oxalate and 

 Rmmonium formate. 



