386 AGRICULTURAL ANALYSIS 



iron oxid. These are found in the soluble portions. In the in- 

 soluble portions have been found silica, sulfates, lime, magnesia 

 and iron oxid. A sample of commercial ammonium sulfate ana- 

 lyzed by Jumeau contained the following substances: 30 



Per Cent. 



Moisture 10.5109 



Ammonium sulfate 67.8453 



Ammonium thiocyanate ... 9-3935 



Sodium sulfate 9.2429 



Potassium sulfate 0.9774 



Calcium sulfate 0.6800 



Iron thiocyanate 0.5000 



Magnesium chlorid traces 



Silica 0.0830 



Undetermined 0.7670 



The determination of the thiocyanic acid in the thiocyanate 

 is generally made by the oxidation of the sulfur to sulfuric acid 

 and its subsequent weighing in the form of barium sulfate. 

 Jumeau has modified the method by determining the amount of 

 the thiocyanate by means of a titrated liquid. The method is 

 practiced as follows: 



A solution of ammonium thiocyanate is prepared, containing 

 eight grams of this salt per liter, and its exact content of thio- 

 cyanate is rigorously determined by titration with silver nitrate 

 or by the weight of the barium sulfate produced after the oxida- 

 tion of the sulfur. Ten cubic centimeters of the titrated liquor 

 are diluted with water to about 100 cubic centimeters and 10 

 cubic centimeters of pure sulfuric acid added. Afterward, drop 

 by drop, a solution of potassium permanganate is added, con- 

 taining about 10 grams of that salt per liter. The perman- 

 ganate is instantly decolorized. There is an evolution of hydro- 

 cyanic acid as the thiocyanate passes to the state of sulfuric acid. 

 A single drop in excess gives to the mixture the well-known rose 

 coloration of the permanganate solution which persists for sev- 

 eral hours. The number of cubic centimeters necessary to pro- 

 duce the persistent rose tint is noted and the same operation is 

 carried on with from one-half to one gram of the unknown prod- 

 uct which is to be assayed. A simple proportion indicates the 

 80 Revue de Chimie analytique applique'e, 1893, 1:51. 



