282 JOURNAL OP ECONOMIC ENTOMOLOGY [Vol. 2 



posure should be made in order that the gas may be considered a fairly- 

 sure preventive." He also reached the conclusion: 



''In fumigating nursery trees at the normal recommended strength, 

 viz, 1 ounce of cyanide to 100 cu. ft., the duration of exposure 

 should be 1 hour, and if less time is desired the strength of the gas 

 may be increased with perfect safety to the trees, and insure as far 

 as possible the killing of any scale that may be present." 



While we had concluded from our various experiments and obser- 

 vations that a 60 minute exposure is preferable to a shorter length 

 of time in ordinary nursery work, it was decided to call attention to 

 these facts in a circular letter to state nursery inspectors, and re- 

 quest from them an opinion in regard to the length of exposure. Re- 

 plies were received from 29 inspectors, practically all of whom ex- 

 pressed the opinion that a 45 minute exposure to the ordinary 

 strength of gas is sufficient to kill the San Jose scale under best con- 

 ditions of exposure, etc. All appeared to agree also on the point 

 that no injury need be expected to dormant nursery stock even 

 though exposed to the gas for a much greater period. 



Mr. J. A. West of Illinois called attention to injury from fumigat- 

 ing cherry stock both in the fall and spring. Mr. Berger states that 

 45 minutes' exposure to a dose of 1 ounce is injurious to citrous nur- 

 sery trees, but that the trees will stand this strength of gas if the 

 roots are covered, so as to protect them from the gas. 



Of the 29 entomologists replying to the above circular, one is recom- 

 mending a 30 minute exposure, twelve a 40 minute exposure, four 

 a 45 minute exposure, two a 50 minute exposure, and five a 60 

 minute exposure. Several did not express themselves in letter of 

 reply, while nine who are recommending a less exposure, stated they 

 had about decided to recommend a 60 minute exposure, or inclined 

 strongly towards this recommendation. 



At a meeting of the American Association of Horticultural In- 

 spectators, held in Washington, D. C. November, 1903, the 1-2^ 

 formula was adopted and has now come into use generally. There 

 appears, however, to have been a lack of any very definite experiments 

 as to the chemical combination of the materials used in generating 

 this gas, upon which to base this recommendation. 



Recent work by ]\Ir. R. S. Woglum, of the Bureau of Entomology,^ 

 m conjunction with the Bureau of Chemistry, appears to throw some 

 light on the subject. From these experiments, it seems that 2 parts 

 of water to 1 part each of acid and cyanide produces the maximum 



"See bulletin No. 79, Bureau of Entomology, U. S. Dept. Agr. 



