30 



sanguine expectation that all eggs could be killed has failed. While it 

 may be done, and has been done, so many intervening causes, especially 

 the difficulty of keeping a tent gas tight, in a treatment of an orchard, I 

 dare say the only practical way of exterminating the insect will be by two 

 treatments — say four weeks apart. The first treatment would exterminate 

 large bugs, everything not in the egg state, and the majority of the eggs. 

 The second, the remainder — all eggs then being hatched. 



Modes of Treatment. 



In Bulletin No. 73 Mr. Morse gives full directions for using the gas. To 

 avoid the injury to the foliage, which, according to the later investigations 

 of Mr. Morse, is due to free ammonia gas, Mr. Morse employed carbonic 

 acid gas, which was generated simultaneously by pouring the mixture of 

 cyanide and carbonate solution together in the receiver. 



The Process. 



I copy the following from Bulletin of Experimental Station, of Berkeley, 

 No. 73: 



Solutions. — The cyanide of potassium solution (nof the "mining cyanide") is prepared 

 by dissolving the salt in the proportion of ten pounds to two gallons of water. Place the 

 cyanide in the vessel in which you wish to make the solution, and add the water to it, 

 bring to nearlj^ boiling, with occasionally stirring, and let it cool. It is best to make the 

 solution one or two days before using, in order to avoid as much as possible the stronger 

 odor of a freshly prepared solution. 



In the prescribed dose an excess of acid has been recommended, in order that complete 

 action shall always take place. It is desirable to test the residue occasionally, to be satis- 

 fied that the work is complete. This is done by adding a little more acid, and noting 

 whether boiling or effervescence takes place upon stirring; care being taken not to mis- 

 take the effervescence from the material accidentally gathered on the sides of the cylinder 

 during the operation for that of material which should have been acted upon in the bottom 

 of the cylinder. 



Doses According to Size of Trees. 



The regulation of the doses for the different sized trees, so as to produce uniform treat- 

 ment, is calculated on the basis of the results of the experiments which determined the 

 amount of each constituent for a twelve-foot tree. The following table indicates the 

 amounts of trees of diflerent dimensions of top, based upon the rates of cubical contents. 



The amount of material for each dose differs from that previously recommended (Bul- 

 letin 71), by a decrease of one fourth in the amount of soda, and a slight change in the 

 acid; the cyanide remains the same. Varying amounts of soda were used, showing quite 

 clearly that a decrease of one fourth was possible, but further than this an appreciable 

 lessening in the preservative effect was noticeable. 



