36 BULLETIN" 730, U. S. DEPARTMENT OF AGRICULTURE. 



were dead, but at a depth, of 40 to 50 centimeters (16 to 18 inches), 

 as well as between the stocks in a radial direction, even by nsing five 

 times more water, the result was incomplete. 



EXPERIMENTS AT WINCHESTER, VA. 



Having prepared the basins as described for the use of carbon 

 disulphid in solution, using 8 gallons of liquid to a 4-foot basin, one 

 tree was treated with the solution at the rate of one-half ounce to 4 

 gallons of water, and the second tree at the rate of 1 ounce to 4 gal- 

 lons. The aphids within the treated area were killed. 1 



PREPARATION OF 'THE SOLUTION. 



Sodium cyanid is very soluble in water, and it is therefore not 

 necessary to exercise the same degree of care in preparing the solu- 

 tion as is the case when using carbon disulphid. In the initial experi- 

 ments outlined above the correct amount of sodium cyanid was 

 weighed out and stirred into the water contained in 2-gallon pails. 

 In the more extended field experiments the material was dissolved in 

 a 200-gallon spray tank and run into the basins through the auxiliary 

 tanks described under the "Use of carbon disulphid in solution." 



DOSAGE EMPLOYED. 



Experiments were carried out in which from one-fourth to 2 ounces 

 of sodium cyanid to 4 gallons of water were used, and as in the case 

 of carbon disulphid it was found that one-half ounce of sodium 

 cyanid to 4 gallons of water was the most satisfactory. 



THE EXTENT OF THE LATERAL AND VERTICAL DIFFUSION OF THE GAS BEYOND THE 

 RANGE ATTAINED BY THE LIQUID. 



The particular experiment (p. 32, fig. 1) made to determine whether 

 the fumes of carbon disulphid diffused laterally beyond the range of 

 the liquid was repeated with sodium cyanid. The results were the 

 same in both instances, namely, the fumes of sodium cyanid do not 

 diffuse laterally beyond'the point attained by the liquid in its diffusion. 



Experiments and observations made during the course of the work 

 confirmed the opinion of Mouillefert, recorded above, that the gas 

 from the dissolved cyanid did not diffuse evenly or produce aphid 

 mortality to the lowest depths attained by the liquid in the case of 

 carbon disulphid. 



No difficulty was encountered in killing the aphids at shallow 

 depths when the liquid was used at the rate of three-fourths gallon 

 per square foot of soil area, but the aphids forming the deeper in- 

 festation invariably escaped. This was the case even in moist, light 

 soils, where the foregoing quantity of water will penetrate to a con- 

 siderable depth. 



1 The aphid infestation on these trees was shallow. 



