106 



THIRTY-FOURTH FRUIT-GROWERS^ CONVENTION. 



ably from that in practice with others. The estimation of dosage in 

 use to-day is entirely guesswork. Measurements of trees are made 

 by the eye, consequently successful results depend largely upon the uni- 

 formity of the estimator's eyesight, supported by his experience in 

 fumigation. Under this system of guesswork, however, the results 

 secured by some f umigators has been most excellent ; by others, not 

 as satisfactory as could be desired. 



Having grasped the exact situation of the present system, it wa.s 

 realized that one of the very first problems before this investigation 

 was the establishment of a basis upon which to build up a fumigation 

 dosage with accuracy and definiteness. The only way in which to 

 obtain this end is through the determination of the cubical contents 

 of the space enclosed by the fumigating tent, and dosing the tree in 

 proportion to the contents. In our work, measurements are made 

 over the top of the tent and around the bottom. With these measure- 

 ments we are able to determine immediately, and with some degree 

 of accuracy, the cubical contents enclosed by the tent, using therefor 

 calculation tables which we have invented. 



For the generation of hydrocyanic acid gas, as used in fumigation, 

 potassium cyanide, sulphuric acid and water are used. The hydrocyanic 

 acid gas is derived from the action of the sulphuric acid on the cyanide 

 of potassium. The w^ater does not enter into the reaction, but is present 

 merely to assist it. 



A brand of cyanide manufactured by the Roe.ssler & Haaslacher 

 Company, which is used quite universally in Southern California, 

 has been employed in our work. The cyanide has so far proven 

 entirely satisfactory^ 



In the production of hydrocyanic acid gas we have been using the 

 j-equired chemicals at the rate of cyanide of potassium 1 part, sul- 

 phuric acid 1 part, water 3 parts. The water is first measured, then 

 poured into the generator, which is placed beneath the tented tree. 

 The acid is then introduced, followed immediately by the dry, lumps 

 of cyanide. Chemical combinations take place with definiteness: that 

 is, when one chemical reacts on another in the production of a third 

 substance, the proportion of these first two chemicals which enter 

 into the reaction is always the same. Such is the result in the action 

 of sulphuric acid on potassium cyanide. A quotation from a letter 

 received from Mr. J. K. Haywood, of the United States Bureau of 

 Chemistry, serves well to illustrate this point : "In the reaction of 

 commercial sulphuric acid on potassium cyanide, for every part of 

 potassium cyanide % part of sulphuric acid is used up. xVccording 

 to this, % part of sulphuric acid is all that is theoretically needed to 

 convert 1 part of potassium cyanide to hydrocyanic acid. Since it 

 is always best to have some excess of the acid to carry the reaction to 

 completion, the ratio of 1 part of acid to 1 part of cyanide is about 

 correct. In using parts of acid to 1 part of cyanide there is an 

 entire waste of part of acid. It does no good and should not be 

 used. ' ' 



As a further illustration of this point, allow me to mention the 

 result of some tests made along this line. It was desired to determine 

 by experiment if equal parts of acid to cyanide were sufficient to carry 



