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 (A spidiotus aurantit), which was becoming quite 
troublesome in many orchards in Orange County. By 
