MISCELLANEOUS 59 



Aug. 8th. 777,600,000 females lay 120 eggs each. 



Aug. i8th. 93,312,000,000 adults issue, of which 46,656,000,000 



are females. 



Aug. 28th. 46,656,000,000 females lay 120 eggs each. 

 Sept. loth. 5,598,720,000,000 adults issue, of which half are 



females. 



Such figures as these stagger the imagination, and when it is 

 remembered that in the above table it has been assumed that each 

 female has laid only 120 eggs, that is one batch, whereas in reality 

 she may lay four such batches. 



FUMIGATING WITH HYDROCYANIC ACID GAS. 



INTRODUCTION. 



The practice of fumigating greenhouses, conservatories, etc., for 

 the purpose of destroying animal pests is not carried out in this 

 country to anything like the extent it deserves to be, nor is the method 

 of treating trees by sheet tents or box covers. In other countries 

 the practice has during the past few years become widespread, and 

 there has been a great improvement in both equipment and methods. 



Recently Mr. Walter W. Froggatt, the Government Entomologist 

 of New South Wales, has drawn my attention to the different 

 quantities that are used by different operators, and in looking up the 

 work carried out, I have been led to make various experiments for 

 myself, and it is upon these materials that the present remarks are 

 based. 



THE CHEMICALS REQUIRED. 



The chemicals necessary for generating hydrocyanic acid gas are 

 potassium cyanide of 98 per cent, purity, sulphuric acid, and water. 



A stone or pot vessel is used, into which the measured quantity 

 of water is placed ; the necessary amount of acid is next added, which 

 rapidly increases the temperature of the mixture, and whilst still hot 

 the cyanide is added. It is important to remember that the cooler the 

 mixture is allowed to become, the slower will be the generation of 

 gas and a decrease in the amount. 



Certain writers have very properly emphasised the importance of 



