THIRTY-FOURTH FRUIT-GROWERS ' CONVENTION. 



107 



the reaction to completion in the liberation of hydrocyanic acid gas. 

 For this test two series of generators were placed in line. In one 

 series equal parts of acid and cyanide were used; in the other series 

 114 parts of acid to one of cyanide were nsed. Three parts of water 

 were used in all cases. The amonnts of cyanide used ranged from 1 

 to 10 ounces ; that is, in one generator was placed 1 ounce of cyanide, 

 1 ounce of sulphuric acid and 3 ounces of water; in another of the 

 same series, 2 ounces of cyanide, 2 of acid and 6 of water, and so on 

 in the same proportion up to 10 ounces. The second series was identical 

 with the first, except for the use of 14 more acid than cyanide. After 

 generation had taken place for about an hour and a half an examination 

 was made of the residue. In the first series, in which equal parts of 

 acid and cyanide were used, the residue was in the form of a liquid. 

 In the second series, in which li/l times as much acid as cyanide was 

 used, the residue in several plots had collected in a mushlike mass. 

 Puzzled at first over this phenomenon, and in order to aseertaiii if 

 cyanide still remains unchanged in the residue, sulphuric acid was 

 added, but without further evolution of gas. This at once dem- 

 onstrated that all the available cyanide had been digested. Residue 

 from some of these vessels was sent to Washington for analysis. The 

 analysis showed that the reaction was as complete Avhere equal 

 parts of acid and cyanide were used as where ly^ parts of acid to 

 1 of cyanide were used, and in all cases the reactions ^vere as satis- 

 factory as could be desired. Of all the samples of residue analyzed, 

 in no case did the amount of cyanide lost exceed 2 per cent. In sub- 

 mitting the result of this analysis, Dr. Wiley, Chief of the Bureau 

 of Chemistr}^ wrote : ' ' The amount of cyanide present in these samples 

 is so small that it does not indicate to us incompleteness of reaction, 

 but rather indicates the amount of hydrocyanic acid dissolved in the 

 water. This view of the case is strengthened by the fact that increas- 

 ing the amount of sulphuric acid in the cases above has not decreased 

 the amount of cyanogen present in the residue. From our work, there- 

 fore, we are of the opinion that the same amount of sulphuric acid as 

 potassium cyanide is a plenty to carry the reaction to completion." 

 Thus, we have determined that equal parts of sulphuric acid to 

 potassium cyanide is sufficient for a complete reaction. The adoption of 

 three parts of water was entirely arbitrary. In all our work no injury 

 to the tree has resulted in the use of three parts of water, therefore we 

 see no reason for increasing the amount. Whether the amount can be 

 decreased or not with safety we hope to determine during our future 

 work. 



But why in the experiment just mentioned did the residue of gener- 

 ators in which ly^ parts of acid Avere used congeal, while that of those 

 generators in which equal parts of acid and cyanide were used remain 

 entirely in liquid form ? Let me explain. When sulphuric acid acts on 

 potassium cyanide, hydrocyanic acid, a gas, and potassium sulphate, a 

 solid, are formed. If enough water is present, the potassium sulphate 

 dissolves so that no residue is left. This is what happened when equal 

 parts of acid and cyanide were used. When, however, 14 more "acid 

 than cyanide is used there is an excess of acid. The potassium sulphate 

 is not as soluble in water containing this excess acid as it is in water 

 alone, hence it partly crystallizes out. 



