458 



1 next operated on larger orange trees by using a 40-gallon barrel in 

 the same manner that I had the tin can. After making a series of ex- 

 periments with this barrel I had a tent made out of unbleached muslin, 

 and afterwards had it oiled with boiled linseed oil; with this tent I 

 could operate on trees about five feet high. I next used a tent belonging 

 to Mr. J. W. Wolfskin, of this city ; this tent was made out of heavy 

 ducking, and was large enough to treat trees ten or twelve feet in height. 

 It was simply oiled with boiled linseed oil, and was placed over the trees 

 by the aid of poles. In making these experiments I was aided by Mr. 

 Alexander Craw, Mr. Wolfskill's foreman, and the experiments were 

 made at all hours of the day and also at night. 



At first I dissolved the cyanide in cold water, then used it with water 

 but undissolved, and later I used the cyanide dry. 



In all of these experiments I used commercial sulphuric acid, undi- 

 luted, for the purpose of generating the gas. No machine of auy kind 

 was used for the purpose of circulating the gas inside of the tent, and 

 the gas was generated within the tent or other appliance used for inclos- 

 ing the trees. 



Shortly after making these experiments Mr. J. W. Wolfskill had a 

 fumigator constructed for operating oq tall trees, and he had the entire 

 upper part of his fumigating tent painted black for the purpose of ex- 

 cluding the rays of light, as my previous experiments with the un- 

 painted tents demonstrated the fact that trees treated in the hottest 

 part of the day were more liable to be injured by the gas when an over- 

 dose of it had been used than they were when treated in the cooler 

 portion of the day or at night. In conjunction with Messrs. Wolfskill 

 and Craw I made a large series of experiments with this fumigator both 

 during the daytime and also at night. 



All of my experiments with hydrocyanic acid gas, referred to above, 

 were made in the latter part of the year 1886, and they demonstrated 

 the* following facts : 



(1) That when the aqueous solution of cyanide was used, the trees 

 were more liable to be injure d bj' an overdose of the gas than when the 

 cyanide was used dry. 



(2) That trees treated in the hottest part of the day were more liable 

 to be injured by an overdose of the gas than if treated in the cooler 

 portion of the day or at night. 



(3) That the use of a black tent in the daytime somewhat prevented 

 injury to the trees by the gas, but only to a comparatively slight 

 degree. 



In the spring of the year 1887, Prof. E. W. Hilgard, of the State Uni- 

 versity of California, delegated one of his assistants, Mr. F. W. Morse, 

 to carry on a series of experiments with various gases for the destruc- 

 tion of insects on Citrus trees, and after testing several different kinds 

 of gases he found none so effectual as hydrocyanic acid gas, which he 

 generated by means of an aqueous solution of potassium cyanide and 



