530 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 4 



with an aspirator of one litre capacity and it in turn connected with 

 a vacuum filter pump fitted to the water faucet. 



In order to get the full value of the air bubbles as gas conveyors 

 a "Cottrell spiral" of very fine platinum wire is inserted in the end 

 of a glass tube drawn down to a fine point and this tube runs through 

 the cork in one neck of the Woulff bottle and a similar one placed 

 in the KOH flask and the air in passing through them is thus broken 

 up into tiny bubbles. 



When a jar or a series of vials containing the scale or other insects 

 is ready for treatment, all connections are made gas tight, the proper 

 amount of acid added to the cyanide solution and the vacuum pump 

 started. As soon as sufficient vacuum is created in the fumigating 

 jar or vials, a stream of air comes bubbling through the cyanide solu- 

 tion, conveying the gas into the jar or vials, and through them into 

 the KOH solution where it is collected for titrating. 



In order to allow of a thorough diffusion of the gas in the jar or 

 vials, the pump is kept running for about fifteen minutes or 15 litres 

 of gas run through. A fresh solution of KOH is then placed in the 

 flask and two litres of gas, as measured by the aspirator, is run through 

 and collected in the flask for titration. 



The KOH solution is now titrated with silver nitrate (AgNoa) 

 solution using a N/lOO solution instead of N/lO as the reaction with 

 the weaker solution is more delicate and more easily controlled. 



For measuring the titrate solution we use a 100 cc. Mohr's burette 

 graduated to 0.1 cc. 



For containing the insects we use the size gelatine capsules, placing 

 one or more insects in each capsule and one or two capsules in each 

 vial. In fumigation the caps are removed from the capsules and 

 afterward replaced. A series of living insects placed in capsules and 

 subjected to the same conditions as to temperature, moisture, etc., 

 but leaving out the cyanide treatment is kept as checks for each 

 series of treated insects. 



For keeping a record of each experiment a card, designed by Professor 

 Woodworth, is used. This card contains appropriate headings for 

 recording the locality, date, temperature, time, weight of cyanide, 

 etc., and numbered spaces for thirty insects. When running series, 

 we use one card for each percentage of gas, dividing the spaces into 

 four lots, allowing one space for recording the living check and six 

 spaces for recording the treated insects in each lot. The squares 

 containing the numbers for treated insects are colored yellow with 

 India ink while those for the checks are left white. This arrangement 

 being of considerable assistance to the ej^e in recording quickly and 

 accurately. 



