222 THE PRINCIPLES OF FLORICULTURE 



strength of cyanide, but who uses the 50 per cent cyanide, which 

 is the usual strength kept at drug stores, instead of the 98 to 

 99 per cent material, will of course, get results widely different 

 from those obtained by persons using the stronger article. We 

 must use standard materials, then, if we use the same formula 

 in their preparation." 



261. Purity, of the cyanide. " Three materials are necessary 

 potassium cyanide, sulphuric acid and water. We have to 



consider their quality and the quantity to use. 



" It is important to use a cyanide which is practically pure. 

 The 98 to 99 per cent grade manufactured by Merck is a reliable 

 material, and the products of similar strength made by a number 

 of other manufacturers are also satisfactory. With lower grades, 

 less of the material from which the gas is formed is of course, 

 available, and there is also a question as to what result the pres- 

 ence of other substances may produce. With 50 per cent cya- 

 nide, for example, there would be only half as much cyanogen 

 to combine with the hydrogen of the sulphuric acid as with the 

 98 to 99 per cent grade, and if among the constituents of the 

 other 50 per cent there should be something which would com- 

 bine with the hydrocyanic acid gas as fast as it formed, there 

 might be little or none of the gas left to do its work. Therefore, 

 use a practically pure potassium cyanide." 



262. The sulfuric acid. " Perhaps the sulphuric acid is the 

 most variable of the three factors used in fumigation. At least, it 

 is exceedingly important that it should meet certain requirements 

 if the treatment is to be satisfactory, as the use of a wrong grade 

 of acid is liable to cause injury to the foliage. Commercial 

 sulphuric acid is satisfactory, provided it contains no nitric acid, 

 and is of the strength known as 66 Baume. Such an acid should 

 average 93 to 94 per cent of actual sulphuric acid, the other 6 or 

 7 per cent consisting of impurities of various kinds. Sulphuric 

 acid is made either from free sulphur or from sulphur combined 

 v with iron or copper and known as pyrites. Ordinarily, the pyrites 

 used, contains arsenic and other materials of a like nature. In 

 the manufacture it becomes mixed with fumes of nitric acid 

 gas, and when pyrites is used rather than sulphur, much more 

 nitric acid becomes mixed with the sulphuric acid produced, than 

 in the case where sulphur is taken. The nitric acid can be removed 

 by refining, of course, but this increases the cost. 



" The danger in having nitric acid present, is that it is energetic 

 in its action, and also volatilizes readily. Accordingly, when 

 sulphuric acid containing it, is added to water, the heat produced 

 begins to volatilize the nitric acid, and when the cyanide is 



