37 AGRICULTURAL ANALYSIS 



and the distillation may be finished within 30 minutes, thus secur- 

 ing a saving of time. There will doubtless be a slight corro- 

 sion of the flasks by the sulfid employed, but where the gunning 

 oxidation process is practiced this danger would be avoided. 



320. The Gunning Moist Combustion Process. The modifi- 

 cation proposed by Gunning was based upon the observation that 

 in the ordinary kjeldahl process the excess of sulfur trioxid in 

 the beginning of the operation soon escapes or unites with water 

 in a form not easily decomposed. 11 During the progress of the 

 combustion the acid diminishes in strength until it is below the 

 concentration represented by the formula H 2 SO 4 , and in this 

 diluted condition the oxidation takes place more slowly. Gun- 

 ning proposes to avoid this difficulty by mixing potassium sulfate 

 with the sulfuric acid. This salt forms with the sulfuric .acid, 

 acid salts which, by heating, lose water easier than acid, and, as 

 is well known, they not only act as decomposing and oxidizing 

 media as well as sulfuric acid, but even in a higher degree, re- 

 sembling the action of sulfuric acid at high temperatures and 

 under pressure. 



By heating this mixture of sulfuric acid and potassium sulfate 

 with organic matters in an open vessel, not only the water origi- 

 nally present, but that which is formed during the oxidation, is 

 driven off without loss of acid. For this reason instead of the 

 oxidizing mixture becoming weaker, the acid becomes stronger, 

 the boiling-point rises and this, combined with the fluidity of 

 the mass, favors the decomposition and oxidation of the organic 

 matter in a constantly increasing ratio. 



The original mixture used by Gunning has the following com- 

 position; viz., one part of potassium sulfate and two parts of 

 strong sulfuric acid. The substances are united by heat, and 

 on cooling are in a semi-solid state, melting, however, easily on 

 the application of heat and assuming a condition that permits 

 them to be poured from vessel to vessel. The quantity of the 

 sample should vary in proportion to its nitrogenous content from 

 half a gram to a gram. The combustion takes place in flasks en- 

 tirely similar to those used in the ordinary kjeldahl process. In the 

 11 Zeitschrift fur analytische Chemie, 1889, 28 : 188. 



