162 THE PROTEIN SUBSTANCES. 



beautiful deep bluish-violet rosettes which are composed of long, irregular, right- 

 angled plates. It is quite soluble in cold water. The free acid crystallizes in 

 fern-like formations. Besides this acid SKRAUP obtained two other acids which 

 he calls caseanic acid, C 9 H 16 N 2 O 7 , and caseinic acid, C 12 H 24 N 2 O 5 . The caseanic 

 acid crystallizes, melts at 190 -191, is tribasic, and is probably an oxydiamino- 

 acid. The caseinic acid is dibasic and occurs in two modifications. The one 

 which melts at 228 is faintly dextrorotatory; the other modification melts 

 at 245 and is optically inactive. Both crystallize, but the inactive form does 

 not yield well-defined crystals. Caseinic acid seems also to be an oxydiamino- 

 acid. 



Diaminotrioxydodecanoic acid, C 12 H 28 N 2 5 , is an acid obtained by FISCHER and 

 ABDERHALDEN 1 on the hydrolysis of casein and seems to stand close to SKRAUP 's 

 caseinic acid, but differs from it in its optical properties. This acid is faintly 

 levorotatory : (a) D = about 9. It crystallizes in plates, which grow into rosettes 

 or spherical aggregations. It has a faint bitter taste, gives a crystalline hydro- 

 chloride which is slightly soluble in strong hydrochloric acid, and gives a 

 crystalline copper salt. 



In regard to the methods which are used in the separation and prep- 

 aration of the ammo-acids and other products produced in the hydrolysis 

 of proteins, we refer the reader to larger handbooks and to E. FISCHER'S 

 work, " Untersuchungen iiber Aminosauren, Polypeptide und Proteine," 

 Berlin, 1906. 2 



In order to quantitatively follow the proteolysis, especially the later 

 stages, one can, according to SoRENSEN, 3 determine to advantage the 

 increase in the carboxyl groups which takes place during the progress 

 of the hydrolysis. For this purpose he has worked out a method which 

 is as follows: The amino groups are converted into methylene groups 

 by means of formaldehyde and then the carboxyl groups determined 



N 



acidimetrically by Ba(OH) 2 (or in certain cases by caustic alkali) using 

 o 



phenolphthalein or thymolphthalein as indicator. By this method 

 not only can enzymotic products be titrated, but also products of acid 

 hydrolysis after decolorization by means of silver nitrate. 



SIEGFRIED 4 has found that amino-acids in the presence of alkali or 

 alkaline earths de-ionize carbon dioxide and form salts of the type of 

 the carbamino salts. For example glycocoll in the presence of lime 

 yields with carbon dioxide, calcium carbamino-acetic acid, CH 2 .NH.COO 



COO Ca 



If the nitrogen is determined and at the same time the combined carbon 

 dioxide estimated by means of the calcium carbonate split off on boiling 



PO 

 the filtered solution, then the quotient -^ gives the number of N atoms 



1 Zeitschr. f. physiol. Chem., 42. 



2 See Hoppe Seyler-Thierfelder, Handb. d. physiol. in pathol. Chem. Analyse, 8 

 Aufl., Berlin, 1909, and also Abderhalden in Handb. der Biochem. by C. Oppenheimer, 

 Bd. 1, p. 347. 



3 Biochem. Zeitschr., 7; with Hansen, ibid., 7. 



4 Zeitschr. f. physiol. Chem., 44 and 46; with Neumann, ibid., 54; with Lieber- 

 mann, ibid., 54. 



