90 



form is at the bottom of the tree, while with the pot or portable 

 generator the greatest toxicity is at the top. Besides scale- insects, 

 75,000 Cocinellids have been used to obtain the index of results. 

 The greatest possible peld is 108 lb. or 18-56 U.S. gals, of anhydrous 

 liquid hydrocyanic acid from 200 lb. sodium cyanide (51-52 per cent, 

 cyanogen). The amount of liquid hydrocyanic acid (95-98 per cent.) 

 that has been recovered during the past year has been about 78 per 

 cent, of the total available. The amount of gas evolved by the pot 

 or portable generator is estimated at 90 per cent, of the total available 

 gas. During 1918, 75 per cent, of the gas from a given amount of 

 cyanide in the liquid form was made to cover the same ground as 

 90 per cent, from the same amount by the ordinary methods of 

 generation. Thus, while there has been a discrepancy of 10 or 15 per 

 cent, in the actual amount of gas used through the liquid method, 

 the results in the field have not indicated any important difference 

 on the scale-insects experimented with. In the present tests, exami- 

 nations were made of the whole tree including the top. If the results 

 at the centre and bottom only were considered, as is usual in 

 fumigation tests, there was practically no difference between the 

 hquid and the pot methods, and this is confirmed by results in the 

 field. When the centre and top only are considered, the pot method 

 proved more efficient than the liquid. In considering the whole 

 tree, it is found necessary to use about 20 c.c. of liquid hydrocyanic 

 acid (96 or 98 per cent.) to equal 1 oz. of sodium cyanide as given 

 in the schedules of dosage now in practical use. The atomising 

 machines should therefore be graduated to deliver 20 c.c. for each 

 oz. required by the schedules. 



In discussing the physical and chemical properties of Hquid 

 hydrocyanic acid, it is stated that material of 95 per cent, or greater 

 purity is considered a satisfactory grade. As the necessary informa- 

 tion is accumulated it is confidently anticipated that the yield in the 

 future will be equal to or even greater than that now obtained 

 from portable generators. The adoption of the weight basis for 

 commercial transactions in preference to the volume basis is strongly 

 urged. A table is included showing the weights and corresponding 

 volumes of various grades of commercial liquid and the quantities 

 corresponding to various percentages of the maximum yield. The 

 acid is miscible with water in aU proportions and will not stratify 

 upon standing. Hydrocyanic acid evaporates more rapidly than 

 water from dilute mixtures of the two. 



Eeference tables appended to this bulletin, containing data on the 

 specific gravity of commercial Uquid hydrocyanic acid and on the 

 extent of variation of hydrometer readings as affected by temperature, 

 make it possible to determine in a moment the quality of a given 

 Hquid by the use of a hydrometer graduated either in specific gravity 

 or Baume degrees. A cyanometer, i.e., a hydrometer graduated 

 directly in percentages of hydrocyanic acid and provided with a 

 simple table of temperature corrections has been constructed for 

 this purpose. The development of any colour (usually yeUow) or 

 an odour of ammonia indicates incipient decomposition of the Hquid. 

 Factors favouring decomposition are the presence of more than 5 per 

 cent, of water, high temperature, residue from a decomposed Hquid, 



