A CONVKXIKNT TVIM-: OF HYDROCYANIC ACID GAS 



CRNKRATOR FOR FUMIGATIN(^ \INFVARDS 



FOR THE DESTRUCTION OF 11 1 1'. MEALY 



BCG. PSHUDOCOCCUS CAPEXSIS J^.RAIN. 



B}- CiiAKLi-s Wiij.iAM Mallv. M.Sc, I'.E.S.. F.L.S. 



( Plates 2<S-29. ) 



In funiigaiin^^ Ki''H^*^ vines with liydrocyanic acid ^as during 

 the winter season for the destruction of the Vine Mealy Bug, 

 Pseiidococcus capcnsis Brain, it is necessary to use very small 

 amounts of acid and cyanide because of the small space enclosed 

 by the long, low. narrow, gas-tight oiled canvas covers for 

 trellised or " stump" vine (see Plate 29 j. It not only required 

 a great deal of time to weigh or measure off the chemicals, Init it 

 was not easy to drop them into the generating vessel witiioui loss 

 of gas. It was therefore decided to dissolve the c}anide in w ater 

 and use the solution to combine with the acid. 



Different methods of handling the acid and cyanide solution 

 were tried, with the result that the generator illustrated in Plate 

 2^^ was invented. 



It is made of lead (South African Lead Works, Cape 

 Town), and the essential feature is the pair of tubes in the lid. 

 one for acid and the other for cyanide solution. In this 

 generator the lid was perforated and a tube secured across the 

 top to emphasize lateral diffusion as the gas escapes from the 

 generator. But in practice the gas escai)es with such force that 

 this tube is not necessary. A small hole on either side just 

 below the edge of the lid serves the same purp<^se 



To charge the generator the lid is held upside-down, the 

 tubes filled with the proper amount of licjuid, the generator 

 inverted over it and pressed down in position. When ready, 

 introduce the generator under the tent, turn it right side up, and 

 withdraw the hand quickly. The gas is generated instan- 

 taneously and rushes out of the lateral openings in the form 

 of jets, thus allowing am|)le time for the hand to be withdrawn 

 before the gas can diffuse towards the o))cning under the tent. 

 This saves a great deal of time, there is no loss of gas, the 

 generator is easily cleaned and strong enough to stand rough 

 handling b}- coloured boys in the vineyards, and the two lateral 

 openings utilize the force of the chemical reaction to insure the 

 rapid lateral diffusion of the gas. 



BILHARZIASIS: OR THE RISKS Oi- KI\ER BATHlNii. 



Bv Fkkdekk K ( loKDox Cawston". B.A.. .M.I'.. 1-).C.. M.R. C.S. 



L.R.C.P. 



(Noi printed.) 



