CHAP. III.] LEUCINE. 235 



with cold water with frequent stirring, and the solution is separated 

 from insoluble matter by filtering through calico. The insoluble 

 matters are again treated with cold water. The collected turbid 

 solutions, if distinctly acid, are at once boiled : if not, they are first 

 feebly acidified, by means of acetic acid, and then boiled. After 

 separation of any proteid which has been precipitated, solution of 

 acetate of lead is added and the liquid again filtered. A stream 

 of sulphuretted hydrogen is passed through the filtrate, so as to 

 precipitate the excess of lead. After again filtering, to get rid of 

 the lead sulphide, the filtrate is concentrated to a syrupy consistence 

 and then set aside to crystallise. Any leucine which separates may 

 be then purified by the processes referred to in page 236. 



3. By the action of boiling sulphuric acid and other agents. 

 It has already been stated that, by the action of various reagents 

 upon the albuminous and albuminoid bodies, the complex molecule 

 is split up and a large number of products are obtained, some of 

 which may be considered as due to the primary decomposition, others 

 as the result of a secondary action of the decomposing agent upon 

 the bodies first formed. Amongst the principal methods which have 

 been employed with success to effect the decomposition of the 

 proteid molecule, and of which the products have been carefully 

 studied, are the following : 



1. Heating the substance under investigation with solution of 

 barium hydrate under pressure, at temperatures which have in 

 different researches varied between 100 C. and 200 C. This method 

 has been largely employed by Schiitzenberger and by Gautier, by 

 Schultze in association with Barbieri and Bosshard, and has led to 

 results which have afforded a considerable amount of information 

 as to the probable structure of the proteid molecule. 



2. Boiling the substance for many hours with stannous chloride 

 and hydrochloric acid, an inverted condenser being employed and 

 arrangements sometimes made for excluding atmospheric oxygen. 

 (Hlasiwetz and Habermann 1 , E. Drechsel 2 .) 



3. Heating the substance with bromine water in sealed bottles. 

 (Hlasiwetz and Habermann 3 .) 



4. By the action of dilute hydriodic acid on coagulated serum 

 albumin. (E. Drechsel 4 .) 



5. Boiling or fusing the albuminous substances with caustic 

 alkalies. 



1 Hlasiwetz and J. Habermann, ' Ueber die Proteinstoffe, ' Ann. d. Chem. . 

 Pharm., Vol. CLXIX. p. 150. 



2 E. Drechsel, ' Zur Kenntniss der Spaltungsproducte des Caseins.' Du Bois 

 Raymond's Archiv, 1891, p. 254. See also the various papers by Drechsel and his 

 pupils, under the heading Lysiue and Lysatinine. 



3 Hlasiwetz and Habermann, 'Ueber die Proteinstofife,' Annalen der Chemie, 

 Vol. CLIX. p. 304 et seq. 



4 E. Drechsel, 'Ueber die Einwirkung von verdiinuten Sauren auf Albumin. 

 Ludwig's Festgabe, p. 83. 



TTNT 



