APPENDICES. 141 



an account of these experiments will be found at the end of this report. 

 Among the numerous gases tried none have given as good satisfaction 

 as the hydrocyanic acid gas ; an account of the discovery of the effects 

 of this gas is given in the paper by Mr. Cra\\-, reproduced above, and 

 need not be repeated here. Several of the other gases experimented 

 with by me have not as yet been given sufficient trial to justify me in 

 reporting either for or against their use as insecticides. 



In the month of April, 1887, several of the fruit-growers of Sau 

 Gabriel, who had become acquainted with the results that Mr. Wolf- 

 skill, Mr. Craw, and myself had obtained from the hydrocyanic acid 

 gas, applied to Prof. E. W. Hilgard, of the California State University, 

 at Berkeley, for a chemist to assist them in experimenting with various 

 gases, and he delegated Mr. F. W. Morse. Mr. Morse experimented 

 with about half a dozen different kinds of gases, but found none so 

 effectual as the hydrocyanic acid gas, which I had used over six months 

 previously. His report will be found in Bulletin No. 15, Division of 

 Entomology of this department. He was the first to use an apparatus 

 for agitating the air in the tent, but this idea appears to have originated 

 with Professor Hilgard, who writes me that he instructed Mr. Morse 

 to always agitate the air in the tent after introducing the gas. 



In the months of September and October, 1886, Mr. Albert Koebele, 

 one of the entomological agents of this department, made a few experi- 

 ments with the liquid bisulphide of carbon, an account of which he 

 gave in his report to Prof. C. V. Riley, published in the report of this 

 department for the year 1886, page 569. The results of these 

 experiments, however, especially those made under a tent, are so 

 discrepant as to leave one in doubt as to the value of the bisulphide as 

 an insecticide. 



During the past season I have made several experiments with the 

 liquid bisulphide, the main object l)eing to devise some method whereby 

 it could be evaporated more quickly than by merely exposing it to the 

 air, but the results of these experiments were not entirely satisfactory. 

 I next manufactured the bisulphide by passing the vapours of sulphur 

 over red-hot charcoal and conducting the gaseous bisulphide into the 

 tent ; but the numerous experiments I have made with the bisulphide 

 thus produced indicate that it can never be successfully used for the 

 destruction of insects on trees. 



The Tent. — The tent used in enclosing the tree is of the usual 

 circular form, with a conical or dome-shaped roof. It is usually made 

 out of heavy bed-ticking, and is afterward thoroughly oiled with boiled 

 linseed oil ; care should be exercised not to leave the tent folded or 

 rolled up while still damp with the oil. A tent belonging to Mr. J. 

 W. Wolfskin of this city had been recently oiled, and when nearly 

 dry was rolled up and thrown upon the ground where the sun shone 

 upon it ; this was in the forenoon, and when it was unrolled the next 

 morning the greater part of it was found to be charred, as if by fire. 



It would be desirable to use some kind of ready-prepared cloth for 

 making the tent, but thus far no substitute for the oil-cloth has been 



