AGRICULTURAL ANALYSIS 



Many of these minor changes have tended to simplify the pro- 

 cess, but without affecting the principle of the method in the 

 least. 



2. In the second place a class of changes may be mentioned in 

 which there is a marked difference in the method of effecting the 

 oxidation secured by the introduction of a substance, usually a 

 metal, during the digestion for the purpose of accelerating the 

 oxidation. In the original process the only aid to oxidation 

 was applied at the end of the digestion in the use of potassium 

 permanganate. In the modifications now under consideration a 

 metallic oxid or metal is applied at the beginning of the diges- 

 tion. Copper and mercury are the metals usually employed. A 

 separate paragraph will be given to the description of this modi- 

 fication known as the process of Wilfarth. 



3. The third class of changes is even more radical in its nature, 

 having for its object the adaptation of the moist combustion 

 method to oxidized or mineral nitrogen. The chief feature of 

 this class of changes consists in the introduction of a substance 

 rich in hydrocarbons, and capable of easily forming nitro com- 

 pounds, for the purpose of holding the oxids of nitrogen which 

 are formed during the combustion and helping finally to reduce 

 them to the form of ammonia. The chief varieties of this class 

 of changes were proposed by Asboth, Jodlbauer, and Scovell, 

 and will be fully set forth in separate paragraphs. 



313. Method of Wilfarth. The basis of this modification as 

 already noted rests on the fact that certain metallic oxids have 

 the power of carrying oxygen and thus assisting in a catalytic 

 way in the combustion of organic matter. 2 The copper and mer- 

 cury oxids are best adapted for this purpose and experience has' 

 shown that mercuric oxid, or even metallic mercury gives the 

 best results. The manipulation is carried out as follows : 



From one to three grams of the sample, according to its rich- 

 ness in nitrogen, are heated with a mixture of 20 cubic centimeters 

 of acid containing two-fifths fumfng and three-fifths ordinary sul- 

 furic acid. To this is added about seven-tenths gram of mer- 

 curic oxid prepared in the wet way from a mercury salt free of 

 * Chemisches Ceutral-Blatt, 1885 : 113. 



