ECONOMIC USE OF HYDROCYANIC ACID GAS 5 



this idea, so that in most of the earlier work elaborate 

 provision was made for the mixing of the gas and the 

 air contained in the tent. Generally some form of 

 blower connected with the generator was used. How- 

 ever, later work has demonstrated that this is of minor 

 importance. 



The first theory of Mr. Coquillett was that the 

 mixing, or perhaps the combination, of the gas with 

 water rendered it more injurious. Both of his proc- 

 esses were based on this idea. He explained the 

 effectiveness of the soda process as arising from the 

 affinity of the carbonic acid for water. Mr. Morse's 

 original ideas are not made plain in his writings, but 

 his later studies led him to believe that the develop- 

 ment of ammonia in the gas was the most important 

 cause of injury. The injurious effects of ammonia 

 are well known, and he demonstrated the presence 

 of ammonia in the gas, especially in that generated 

 from a solution of cyanide. Thus there were two 

 theories accounting for the good effects of the methods 

 then known, and both agreed in favoring the dry gas 

 process. The latter theory seems to have had more 

 foundation in fact, but it soon became evident that 

 there were other still more important factors determin- 

 ing the injury to the foliage. 



The successful introduction of ladybirds from Aus- 

 tralia into California, and the promising results of the 

 importation, caused the gas method to remain at a 

 standstill for some time. The interest in fumigation 

 was later revived, however, on account of the red 

 scale {Aspidiotus aurantii}, which was becoming quite 

 troublesome in many orchards in Orange County. By 



