AGRICULTURAL ANALYSIS 



in the digestion flask with the desiccated sample. The strongest 

 sulfuric acid is added in sufficient quantity, not less than 10 cubic 

 centimeters in any case, to secure complete decomposition. The 

 acid must be free of ammonia and be kept in such a way as not 

 to absorb ammonia from the atmosphere of the laboratory. To 

 guard against danger of error from such an impurity, frequent 

 control determinations should be made. In control experiments 

 one or two grams of pure sugar are used as the organic matter. 

 If the acid employed contain traces of ammonia, the necessary 

 corrections should be made in each analysis. 



The flask having been charged is placed on a wire gauze over 

 a small flame. The organic matter becomes black and tar-like, 

 and soon there is a rapid decomposition, attended with the evolu- 

 tion of gaseous products, among which sulfur dioxid is found. 

 To avoid danger from spurting, the digestion flask is placed in an 

 oblique position. The flask should have a capacity of at least 

 loo cubic centimeters, and a long neck and be made of a kind of 

 glass capable of withstanding the action of the boiling acid. Par- 

 ticles of the carbonized organic matter left on the sides of the 

 flask by the foaming of the mass at first are gradually dissolved 

 by the vapors of the boiling acid as the digestion proceeds. The 

 action of the sulfuric acid is not entirely finished when gases 

 cease to be given off, but the digestion should be continued until 

 the liquid in the flask is clear and colorless, or nearly so. Usually 

 about two hours are required to secure this result. When aided 

 by the means mentioned below, the time of digestion can be very 

 materially shortened. By adding some fuming sulfuric acid, or 

 glacial phosphoric acid, the dilution caused by the formation of 

 water in the combustion of the organic matter can be avoided. 

 For albuminoid bodies it is hardly necessary to continue the 

 combustion until all carbonaceous matter is destroyed. The full 

 complement of ammonia is usually obtained after an hour's com- 

 bustion, even if the liquid be still black or brown, but with other 

 nitrogenous bodies the case is different, so that upon the whole 

 it is safest to secure complete decoloration. 



The temperature must be maintained at the boiling-point of 



