802 Report or THE DEPARTMENT OF ENTOMOLOGY OF THE 
always a marked odor of hydrocyanic acid gas to the leeward 
of the trees. Hence conclusions as to what can be accomplished 
by fumigation with the above gas should not be based upon 
results obtained with tents. 
CONCLUSIONS. 
Excluding conditions where tents were used, the results of 
tests for 1900-1901 show that with good covers, debarring acci- 
dents and infestation from other sources, fumigation with hydro- 
cyanic acid gas can be depended upon to exterminate the San 
José scale, on medium sized orchard trees, over small areas. 
Under favorable conditions, the scales were all killed by the 
use of .15 gram per cu. ft. (one-half ounce of potassium cyanide 
per 100 cu. ft.), but as shown later, at least double this amount- 
should be used unless the operator is certain that all conditions 
are favorable. 
AMOUNT AND GRADE OF CHEMICALS TO USE. 
Writers on fumigation with hydrocyanic acid gas have recom- 
mended the use of various formulas. The principal variations 
are in the amounts of acid and water used. Coquillet,! Marlatt? 
and Webster? have recommended the use of one part by weight 
of potassium cyanide, one part by volume of sulphuric acid, and 
two parts by volume of water. Based on the weight of potas- 
sium cyanide, the charge would be represented by the formula 
1-1-2. Smith* recommends a formula of 1-1-8. Johnson® and 
Gould® have recommended the use of 1-14-24; while Craw’ rec- 
ommends 1-1j-8. The author has recommended the use of 
1-14-4. The latter was based on results obtained in all-night 
treatment of forcing houses and in nursery fumigation, where 

Insect Life, 2:208 (1890). 
?Year Book U. S. Dept. Agr. 1896:228. 
*Ohio Agr. Exp. Sta. Bul. 103 (1899). 
‘Rept. N. J. Agr. Coll. Exp. Sta., 1897:467. 
®°Md. Exp. Sta. Bul. 57:79 (1898). 
®°Md. Exp. Sta. Bul. 73:163 (1901). 
™Fourth Rept. St. Board Hort. Cal. 1894:107. 
