224 TEE PRINCIPLES OF FLORICULTURE 



ering the pieces of potassium cyanide not already acted upon, 

 so that the sulphuric acid cannot reach these pieces to combine 

 with them and produce gas. For this reason, then, too much 

 acid is as undesirable as too little, and if after a fumigation has 

 been completed, there is a solid or a slushy substance left in the 

 dish, this indicates that either too little water or too much acid 

 was used." 



265. The action of the water. "At present, then, the proper 

 amounts to use seem to be one part by weight of cyanide, and 

 one part by measure of acid. 



" Water is not absolutely essential to the production of hydro- 

 cyanic gas by the action of sulphuric acid on potassium cyanide, 

 as the acid could be poured directly upon the cyanide, and some 

 gas be given off. The process would quickly come to an end, 

 however, in this case, as the potassium sulphate formed would so 

 coat over the cyanide that the acid would either fail to reach it 

 or would do its work too slowly. Water is useful in dissolving 

 both the cyanide and the potassium sulphate produced, and in 

 hastening the chemical reaction, which is of importance, as the 

 maximum amount of gas is needed as quickly as possible for 

 effective results. If too little water is present, the potassium 

 sulphate tending to coat the cyanide is not dissolved, and this 

 delays the process if it does not in part prevent it. Then the 

 heat produced by mixing the acid and the water is a great 

 advantage, as it hastens the chemical reaction. 



"It is evident that too little water will prevent the production 

 of the maximum amount of gas. Experiment shows that too 

 much water acts in the same way, more of the gas entering the 

 water and thus reducing the amount in the air. A series of tests 

 using varying amounts of water has shown that for the best 

 results, there should be three times as much water as acid, and 

 the best proportions of all three materials to use, therefore, be- 

 come : cyanide, one part by weight ; acid, one part by measure ; 

 water, three parts by measure." 



266. The right order in mixing. " It is desirable to utilize the 

 heat produced by the addition of the sulphuric acid to the water, 

 in order to hasten the production of hydrocyanic acid gas. 

 Accordingly, the water should be placed in the jar first, and as 

 the heat produced by adding the sulphuric acid is considerable, 

 granite-ware dishes are preferable to earthenware ones, since 

 the latter frequently crack from the heat. The sulphuric acid 

 should be added to the water, and while hot, the cyanide should 

 be dropped into the rest. 



" To destroy any particular kind of insect, at least a certain 



