18 



CIRCULAR 3 7 3, U. S. DEPARTMENT OF AGRICULTURE 



side of the car. By this revised procedure the fumigation of the 

 cars was conducted for several seasons with very satisfactory 

 results. 



TESTS WITH COMMERCIAL PRODUCTS 



The appearance on the market of several compounds that pro- 

 duce hydrocyanic acid gas suggested the desirability of finding out 

 how effective these materials were against the beetle and whether or 

 not they might be used as alternative fumigants. Accordingly, in 

 1930, a series of comparative tests was begun with five materials 



designated by num- 

 ber as follows: 



No. 1. A crude cal- 

 cium cyanide, made 

 by treating calcium 

 cyanamide with 

 carbon and alkaline 

 salts, and contain- 

 ing between 40 and 

 50 percent of cal- 

 cium cyanide, in ad- 

 dition to impurities. 

 No. 2. A commer- 

 cial calcium cyanide, 

 made by treating 

 lime with liquid 

 hydrocyanic acid. 

 This material con- 

 tains approximately 

 88 percent of cal- 

 cium cyanide, cal- 

 culated from the 50 

 percent cyanogen 

 content guaranteed 

 by the manufactur- 

 ers. (This was the 

 product indicated 

 in the recommenda- 

 tions , previously 

 mentioned, for re- 

 frigerator-car fumi- 

 gation.) 



No. 3. A com- 

 mercial preparation 

 containing hydrocyanic acid, plus chloropicrin as a warning gas, ab- 

 sorbed on granular infusorial earth. This material is sold on the basis 

 of net hydrocyanic acid content, a so-called " 1 -pound can " meaning 

 1 pound of hydrocyanic acid, the weight of the inert material being 

 disregarded. 



No. 4. A commercial preparation containing hydrocyanic acid 

 absorbed in disks of wood-paper pulp. This material is also sold 

 on the basis of the hydrocyanic acid content, rather than the total 

 weight of the contents of the can. 



No. 5. Commercial sodium cyanide (96-98 percent NaCN). In all 

 tests run with this material it was added to water and sulphuric 



Figure 13. — Method of applying" powdered calcium cya- 

 nide through the hatch into a container in the ice 

 compartment. 



