306 EXPERIMENT STATION EECOED. 



20° C.) was found by the author to be 32.25 gin. when calculated according to 

 Tollen's formula. Other authorities have found this to be from 32.5 to 33 gm., 

 according to the concentration of the dextrose in solution. 



In using this noi'mal weight the actual dextrose scale divisions are found by 

 means of a table or a formula which is accurate for variations in specific rota- 

 tion due to concentration. The advantage in employing the method lies in the 

 fact that the percentage of dextrose is found in one operation without making 

 a preliminary analysis in order to find out how much material is to be weighed 

 out. 



Time factors in the determination of nitrogen and other observations on 

 the Kjeldahl method, P. L. Hibbard (A/j.-?. in Science, n. ser., 32 {1910), No. 

 823. p. ^i76). — "Organic substances such as blood or bone have their nitrogen 

 completely converted into ammonia by boiling 3 hours with 25 cc. of sulphuric 

 acid, 10 gm. potassium sulphate, and i gm. copper sulphate ; in most cases. In 

 distillation of this digestion practically all the ammonia is obtained in less than 

 15 minutes. Bumping of the digestion is prevented by addition of 1 to 2 gm. 

 ferrous sulphate. Using the Ulsch-Street method, only a few minutes are re- 

 quired to change the nitrogen of nitrates to ammonia. During the acid diges- 

 tion loss of ammonia occurs when a large portion of the acid has been driven 

 out by too much or too long-continued heat, but not because the flask is heated 

 by the bare flame above the level of the acid." 



Note on the Kjeldahl estimation of nitrogen in fatty substances, J. A. 

 Brown {Cliem. News, 102 {1910), No. 26U, p. 51).— "Ou distilling off the am- 

 monia into standard acid in the Kjeldahl estimation of nitrogen in such sub- 

 stances as cheese, milk, etc., the author has frequently found that a trouble- 

 some frothing ensues in the alkaline liquor, which compels the operation to be 

 conducted very slowly, and with constant attention, to prevent the alkaline 

 liquor frothing over into the distillate and vitiating the result. . . . 



" The author has found that the fi'othing is caused by traces of fatty acids, 

 which escape decomposition in the digestion with strong H2S04 by volatilizing 

 and condensing firmly, in minute disks, on the long neck of the Kjeldahl flask, 

 where they are with great difficulty, if at all, rinsed back into the tub. These 

 fatty acids appear to be identical with those which constitute the insoluble 

 volatile fatty acids in the Reichert distillation of butters, i. e., the Polenske 

 value. The undecomposed fatty acids combine with the excess of alkali, added 

 for the subsequent distillation of ammonia, to form a soap, which causes the 

 liquid to froth when boiled. This may be prevented by diluting the digested sub- 

 stance, previous to adding excess of alkali, to about 100 cc. with distilled water 

 and boiling briskly until only about 40 cc. remains in the flask. On now making 

 alkaline and proceeding in the usual way, the distillation can be conducted 

 with the greatest rapidity, without even attending to the initial ebullition." 



The formaldehyde method for the estimation of nitrogen in organic sub- 

 stances, A. M. Wright {Trans, and Proc. New Zeal. Inst., 42 {1909), pp. 22k, 

 225). — The author shows that Bennett's method* can be advantageously em- 

 ployed for organic substances such as meat extracts, mixed commercial fer- 

 tilizers, dried tankage, and dried blood. It is carried out as follows : 



" The substance under examination is digested with sulphuric acid and sul- 

 phate of potash until the liquor is clear ; the excess of acid is neutralized with 

 sodium hydrate solution, using pheuolphthalein as the indicator ; a neutral solu- 

 tion of formaldehyde is added, liberating the sulphuric acid present in combi- 

 nation with ammonia ; hexamethylenetetramine is formed, which is neutral to 



o Jour. Soc. Chem. Indus., 28 (1909), p. 291. 



