ANHYDROUS LIQUID HYDROCYANIC ACID FOR 

 FUMIGATION PURPOSES. 



By Charles William Mally, AI.Sc, P'.L.S. 



For the destruction df insect pests on fruit trees by means 

 of hydrocyanic acid gas the usual practice is to generate the gas 

 by the action of dihite sulphuric acid on potassium or sodium 

 cyanide, either ( a ) dry or ( b ) in solution. Either method 

 leaves much to be desired, for it not only takes time and care 

 in preparing the chemicals, but there is also the danger of burn- 

 ing the tents by acid coming in direct contact with them through 

 handling them ; or the absorption of fumes or vapours driven 

 off during the generation of the gas may result in the familiar 

 " rotting " of the canvas. The above factors are of special 

 importance in connection with vineyard fumigation for the 

 destruction of the mealy bug, Pseudococciis capciisis Brain, 

 because the vines, whether trellised or " bush," must be covered 

 with long, narrow sheets of gas-proof canvas, almost the whole 

 of which is in close proximity to the freshly-generated 

 gas by whatever means it is produced. The space enclosed is 

 very small, and hence only a small amount of gas is required. 

 On account of the shape of the tent, the gas should be liberated 

 at several points to secure a quick and uniform distribution. 

 This means ^a number of small generators or points of introduc- 

 tion from an external generator. In military work the trouble 

 with acid and cyanide and generators increases the amount of 

 strict supervision necessary, and the time required to do the 

 work. On going into the matter of possible ways of improv- 

 ing on present methods, I decided to trv to make use of the 

 fact that the gas readil_\- condenses on being subjected to a low 

 temperature, and ])roduces the anhydrous liquid hydrocyanic 

 acid. The matter was discussed with the Government Analyst, 

 Dr. C. F. Juritz, and later on, with the assistance of Mr. W. 

 W. Brighton-AIanning, in arranging the details of a small ex- 

 perimental apparatus, a small quantity of the liquid acid was 

 l^roduced at the Entomological Experiment Station, Rosebank, 

 Cape Province. 



The li(|uid acid proved to be much easier to work with 

 than was anticipated. ( )n testing it with dift'erent insects, 

 T came to the conclusion that the gas arising from the 

 liquid dift'uses more quickly, and is more violent in its action 

 than that from an ordinary generator. This is probably due to 

 the absence of moisture or other impurities, which may, in the 

 case of (icticrator gas, have a retarding effect. If this holds in 

 practical work it is an important item, for it involves a smaller 

 amount of gas or else a shorter exposure. 



