5) 
During 1899 mills were fumigated in Pennsylvania and Ohio, under 
the direction of Professor Johnson, with satisfactory results, and con- 
tinued in later years by and under the direction of Professor Johnson as 
well as by Professor Washburn, State entomologist of Minnesota, Prof. 
H. A. Surface, State zoologist of Pennsylvania, and other State 
officials. In the course of time hydrocyanic-acid gas has come to be 
recognized as the best fumigant for the Mediterranean flour moth. It 
is equally valuable against related moths found in mills, but is less 
effective in destroying flour beetles and grain weevils, and even in 
the destruction of the Angoumois grain moth in corn. Indeed, it is 
not generally recommended for any of the latter pests. 
From what subsequently has been learned of this method, failure 
in some cases was undoubtedly due to impure potassium cyanid and 
to faulty application of the process, since the fumigating vessels were 
rather small for the purpose and permitted a considerable boiling 
over at the top. Much residue also remained; in other words, the 
potassium cyanid was probably too weak, perhaps no stronger than 
50 to 60 per cent pure, as was also the sulphuric acid, which was not 
uséd in sufficient quantity to produce a perfect gas, a considerable 
amount of cyanid remaining unaffected as solid residue in the generat- 
ing vessel. It seems also probable that the cyanid was broken into 
too fine particles, but this detail can not now be remembered. 
Owing to these failures as well as to those of other tests which were 
afterwards made, the suspicion arose that something was wrong with 
the ingredients. A sample of the cyanid used was submitted to 
the Bureau of Chemistry and treated with sulphuric acid, with the 
result that only 54.50 per cent of the amount of hydrocyanic-acid 
gas demanded by theory was found. Analysis showed 51.70 per 
cent potassium cyanid, 2.07 per cent sodium cyanid, and 39.28 per 
cent potassium carbonate, the remainder consisting of sodium chlo- 
rid or common salt and impurities. It will be noticed that this 
cyanid was little more than half as strong as demanded for per- 
fect work; hence, what appeared to be a fumigation at the rate of 
September, 1904, the writer, with Mr. Pratt, undertook the fumigation of a dwelling 
infested by the cigarette beetle (Lasioderma serricorne Fab.), using 1 ounce of cyanid 
to 100 cubic feet of space, which destroyed many beetles. Two weeks later, however, 
the beetles had again accumulated in numbers, showing that neither larvee nor pupz 
had been killed to any extent. Then 3 ounces of cyanid were used with a still longer 
exposure, a total of practically forty-two hours. This killed many larve which 
dropped from the furniture, the principal seat of infestation, although carpets were 
also affected, but many were probably not killed and certainly the eggs were not 
destroyed, as the insects continued to infest the house, with the result that before a 
third fumigation could be given the furniture was disposed of. 
For particulars see pages 68-70, Bul. 54, Bur. Ent., U.S. Dept. Agr., 1905. 
[Cir. 112] 
