DETERMINATION OF THIOCYANATES 385 



and \2.y 2 cubic centimeters of normal alkali be necessary to neu- 

 tralize the excess of the acid. Then the nitrogen is found by 

 the following equations: 20.0 12.5=7.5 an< ^ 7.5X0.014=0.105 

 gram = weight of nitrogen found. Then 0.105X100-^-0. 5=21 

 =per cent, of nitrogen found. 



The distilling apparatus of Aubin is preferred by the French 

 chemists, an apparatus so arranged with a reflux partial con- 

 denser that nearly all the aqueous vapor is returned in a con- 

 densed state to the flask, while the ammonia, on account of its 

 great volatility, is carried over into the receiver. To avoid the 

 regurgitation which might be caused by the concentrated ammo- 

 nia gas coming in contact with the acid, the separable part of the 

 condensing tube is expanded into a bulb large enough to hold 

 all the acid which lies above its mouth. By means of this appara- 

 tus the ammonia is all collected in the standard acid without 

 greatly increasing its volume and the titration is thus rendered 

 sharper. The employment of caustic magnesia has the advan- 

 tage of not decomposing any organic matters or cyanids that may 

 be present. 



If the sample under examination hold part of its ammonia a^ 

 ammonium magnesium phosphate, it will be necessary first to 

 treat it with sulfuric acid in order to set the ammonia free, and 

 then to use enough of the magnesium oxid to neutralize the ex- 

 cess of the sulfuric acid and still supply the two grams necessary 

 for the distillation. When the sample contains a considerable 

 quantity of organic matter it sometimes tends to become frothy 

 towards the end of the distillation. This trouble can be avoided 

 by introducing into the flask one or two grams of paraffin. 



Where carbon dioxid is given off during the distillation, the 

 contents of the receiver must be boiled before titration, or else 

 lacmoid must be used as an indicator instead of litmus. 



337. Determination of Thiocyanates in Ammoniacal Fertilizers. 

 The extended use of ammonium sulfate as a fertilizer 

 renders it important to determine the actual constituents which 

 may be present in samples of this material. The following bodies 

 have been found in commercial ammonium sul fates : Sulfuric 

 acid, chlorin, ammonia, thiocyanic acid, potash, soda, lime and 

 '3 



