Value of Arsenic as an Addition to Kerosene Emidsion. 199 



THE VALUE OF ARSENIC AS AN ADDITION TO THE KEROSENE 



EMULSION. 



BY PKOF. C. V. RILEY. 



In an address which I had the honor to deliver at Riverside last spring, 

 in continuing the question of washes, and more particularly the kerosene 

 emulsion, I made the following suggestion : 



Again, if permanency can be given to the effect of a wash, so that the 

 few insects escaping the first application, or which would hatch oiit there- 

 after, would succumb, such addition would be invaluable ; and though the 

 arsenites are, as a rule, effective chiefly against mandibulate insects (or those 

 which masticate their food), in other words, although the action of these 

 poisons is mainly through the stomach, yet I happen to know from experi- 

 ence that they have also a direct effect by contact. Therefore, I recommend , 

 with considerable confidence, that in this diluted kerosene emulsion there 

 be added a small proportion of arsenious acid, say from two to three ounces to 

 every fifty gallons of wash. This arsenious acid may be prepared and added 

 in various ways. Probably one of the simplest would be to take half a pound 

 of arsenic to half a pound of sal-soda, boil this in one-half gallon of water 

 until the arsenic is dissolved, and mix this with about 100 gallons of the 

 diluted emulsion. A quarter of a pound of London purple to 50 gallons of 

 the diluted emulsion, or even a still greater amount, would, perhaps, serve 

 the same purpose, and be less likely to injure the tree. 



I am aware of the danger of making recommendations that have not 

 yet had thorough trial, but I have already made a few limited experiments 

 (and intend making more) which would seem to justify these, and, at all 

 events, if care be taken not to use too large a quantity of the arsenic, no 

 harm will result from it, either to the tree or to those who use the fruit. 



It gives me pleasure to announce that, so far as the experiments go, 

 they confirm this recommendation, and I submit herewith a portion of the 

 report recently received from one of my agents, Mr. Albert Koebele, on ex- 

 periments in this direction. Also, some further experiments with resin 

 compound and arsenic acid. 



MR. KOEBELE'S report. 



In the main I followed your suggestions, while here in April last, in 

 preparing the kerosene emulsion, viz.: to emulsify with resin compound 

 and use arsenic acid in addition. I am glad that your hopes in this wash 

 are verified. In every instance where your proposed arsenic acid was added 

 either to emulsified kerosene or resin compound, there has been a complete 

 extermination of the scales. 



At first too much of the arsenic acid was used, resulting in more or less 

 injury to trees treated, particularly so in weak washes. 



The best results in preparing the emulsion were obtained by taking one 



