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 ISTEW HAVE]^, COFTsT. 
 
 BULLETIN No. 112, 
 
 JUNE, 1892. 
 
 ON THE GUNNING-KJELDAIIL METHOD AND A 
 
 MODIFICATION APPLICABLE IN THE 
 
 PRESENCE OF NITRATES. 
 
 By A. L. WiNTON, Jr. 
 
 The Giinnbig MetJiod [in absence of nitrates). 
 
 The modification of the Kjeldahl method, proposed by Gunning 
 in 1889, has since been indorsed by a number of well-known 
 chemists. 
 
 The Gunning method is very simple — the only reagents used 
 previous to the distillation with caustic soda being sulphuric acid 
 and potassium sulphate, the latter taking the place of the three 
 reagents — mercury, (oxide or metallic), potassium permanganate 
 and potassium sulphide— ordinarily used. 
 
 The mixture of sulphuric acid and potassium sulphate boils at a 
 high temperature, and, as a rule, oxidizes the organic substance 
 more rapidly than the ordinary mixture of sulphuric acid and 
 oxide of mercury. 
 
 The results obtained by Gunning,* Atterberg,f Van SlykeJ and 
 others, including the writer, on fodders, dairy products, fertili- 
 zers free from nitrates, and various organic substances, show that 
 this method is fully as accurate as the ordinary Kjeldahl method, 
 and, in some cases, gives better results. It is a well known fact 
 that the nitrogen of many alkaloids, azo-compounds and various 
 bodies of the aromatic series cannot be determined by the usual 
 Kjeldahl method, but Gunning and Atterberg have obtained good 
 results on morphine, quinine, indigo and aniline oxalate by the 
 Gunning modification. 
 
 * Fres. Zeit., 28, 188. 
 
 f Chem. Zeitnng, 14, 509. 
 
 X U. S. Dept. Agr. Div. Chem. Bull., 31, 142. 
 
 no. ha. 
 
2 
 
 The chief disadvantage of the method is the frothing wliich 
 occurs during tl)e first part of tlie heating. This fi-othing, Ijow- 
 evcr, causes but little trouble if a flask of at least 500 c.c. ca- 
 pacity (which can afterwards be used for the distillation), is em- 
 ployed and care be taken in adjusting the heat. 
 
 The Gunning mixture is, at ordinary temperatures, half-solid, 
 and must be heated before it can be measured for use. It is 
 therefore best to add 18 grams of potassium sulphate and 20 c.c. 
 of sulphuric acid, separately and in the order named, to the flask 
 containing the substance, shaking a few times before heating. 
 The coarsely powdered sulphate may be conveniently measured 
 out in a cai'tridge-shell adjusted to hold 18 grams and provided 
 with a wire handle. The acid may be added from a graduated 
 cylinder or a burette of wide calibre connected by a siplion with 
 the acid reservoir.* 
 
 After the digestion is completed water should be added before 
 the mixture becomes too cold, otherwise it is difficult to obtain a 
 solution of the solid mass. 
 
 The writer has found that the fertilizer-chemical known in the 
 trade as " High Grade Sulphate of Potash," and costing but a few 
 cents a pound, answers every purpose, and is, in fact, better than 
 the white sulphate of the apothecary, being usually free from 
 moisture and chlorides, the presence of which tends to increase the 
 frothing. 
 
 Following is a comparison of results, obtained by the methods 
 named, on those forms of organic nitrogenous matter which are 
 most commonly used in mixed fertilizers, and on four commercial 
 fertilizers free from nitrates. 
 
 Kjelclahl Melbod. Gunning-KJeldahl Wetiiod 
 
 Cotton Seed Meal 7.06 7.11 
 
 " " 7.10 7.13 
 
 " " 7.10 7.1.5 
 
 " " " 6.95 6.97 
 
 Castor Pomace 5.56 5.59 
 
 Tankage 5.03 5.07 
 
 " 5.72 5.82 
 
 Bone 4.03 4.02 
 
 " 3.92 3.90 
 
 Dry Ground Fish .- - 8.69 8.77 
 
 " " 8.14 8.06 
 
 Peruvian Guano 2.88 2.95 
 
 Mixed Fertilizerf 3.45 3.45 
 
 X 3.00 3.00 
 
 " " § 3.80 3.76 
 
 " " 1.82 1.81 
 
 * Report Conn. Agl. Expt. Station, 1889, 192. 
 
 f Contains 1.89 per cent. Nitrogen in Ammonia salts. 
 
 i '• 1.76" " 
 
 8 " 1.77 " 
 
Tim Modified Method appUcahle in the presence of Nitrates. 
 
 In laboratories where fertilizer analyses are being made, the 
 adoption of the Gunning method wonld tend to complicate rather 
 than to simplify matters so long as in the presence of nitrates 
 nitrogen is determined by another method. 
 
 It is impracticable to add salicylic acid to Gunning's reagent 
 as such a mixture could only be used while hot and it is impor- 
 tant that the temperature be kej^t as low as possible during the 
 early stages of the digestion. It occurred to the writer, however, 
 that Scovell's mixture of sulphuric and salicylic acids might be 
 used in the ordinary way, potassium sulphate being added later 
 in the process in place of mercury. After a number of unsuc- 
 cessful trials — unsuccessful because too much potassium sulphate 
 was used and the boiling point of the liquid became so high that 
 oxides of nitrogen were driven off — the following plan was settled 
 iipon. 
 
 The material, .5 to 1.0 gram, is digested with 80 c. c. of Sco- 
 vell's salicylic acid mixture (30 c. c. of sulphuric acid and 2 gms. 
 salicylic acid) in a flask of 600 c. c. capacity, for two hours with 
 frequent shaking. Two grams of zinc dust are then slowly 
 added, with continual shaking, and tlie flask heated, at first gently, 
 until after a few minutes boiling, dense fumes are no longer given 
 off. Thus far the process is the same as in the Scovell-Kjeldahl 
 method (the oflicial method of the Association of Ofiicial Agri- 
 cultural Chemists) except, that the digestion is continued for two 
 hours, which, in some cases, the writer has found absolutely 
 necessary in order to secure comjjlete solution of the nitrate. 
 Ten to twelve grams of potassium sulphate are next added and 
 the boiling continued for a little time after the solution is color- 
 less or, if iron is present, has a lighc straw color which remains 
 unchanged. On cooling, as the mixture begins to solidify, water 
 is added, at first slowly with shaking, and the distillation with 
 caustic soda is cari-ied on in the usual manner. 
 
 The trials thus far made with this method on nitrates and fer- 
 tilizers containing nitrates, have proved entirely satisfactory. 
 
 In the following table are given the results obtained by the 
 official method and the method here described, together with the 
 percentage of nitrogen in nitrates as determined by the Schulze- 
 Tiemaun method. 
 
 The average of the 25 determinations by the Scovell-Jodlbauer 
 method is 4.64 per cent., by the proposed method 4.65. The 
 greatest discrepancy in any instance is one-tenth per cent., 
 the average discrepancy five onehundredths per cent. In ten 
 cases the proposed method gave the lower result, in 13 cases the 
 higher result. 
 
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