TESTS OF GASES TO DESTROY SAN JOSi SCALE. 797 



cut from each of nine different trees and the scales examined, 

 with the following result : 



Alive 



Dead 



Number alive = 58 per cent. igS 



Ten trees were used in each test with carbon disulphide and 

 carbon tetrachloride except in No. 6, which had nine trees. Five 

 each were used in the acetylene tests, making in all two hundred 

 and twenty-four trees which were fumigated. These were set 

 in nursery rows on the station grounds, where they could be 

 watched during the season. 



Carbon Bisulphide. 



The liquid was volatilized by putting it in iron frying pans 

 heated to about ioo° C, according to the method described in 

 last year's report. The pans were placed on frames above the 

 trees and near the top of the case. The fumigating was done in 

 tin cases containing about six cubic feet. The figures in the table, 

 as well as those in the text, are calculated for one hundred cubic 

 feet. The quantities used, fumigation period and results, are 

 shown in Table I. The effect upon the scales corresponds with 

 the results of last year's tests in that ten fluid ounces or less 

 of the liquid does not kill all of the scales unless acting during a 

 long fumigation period. Thus in Nos. i and 2, ten ounces acting 

 for one and two hours left over twenty per cent, of living scales, 

 but in No. 5, where the same quantity was allowed to act for 

 four hours, all were dead. In Nos. 6 and 9, five ounces did not 

 kill all of the scales in two and four hours, but after being treated 

 for six hours none survived. 



As was the case in last year's tests, twenty or more ounces 

 acting for one hour or longer killed all of the scales. Where 

 thirty ounces acted for two hours, one tree (ten per cent.) failed 

 to grow, though it started and afterward died. 



Though not proven, our tests indicate that the limitations of 

 carbon disulphide vary from a minimum of twenty fluid ounces 

 for one hundred cubic feet with a fumigation period of one hour 

 to a maximum of thirty fluid ounces for two hours. Less than 

 the minimum may not kill all the scales, and more than the max- 



