236 LEUCINE. [BOOK n. 



6. Long-continued boiling with dilute sulphuric acid ; various 

 observers employed acid of different concentration (though the pro- 

 portion of 1 of acid to 3 of water has been most common), the 

 duration of boiling usually varying between 24 and 36 hours. 



By any of these methods of decomposition leucine may be obtained 

 from any of the albuminous or albuminoid bodies, mixed with a large 

 number of other bodies, which are to be looked upon as either 

 primary or secondary products of the decomposition of the proteid 

 molecule. Whilst the first four methods have been employed with 

 the greatest success for the purposes of investigation, the fourth and 

 especially the fifth have been had recourse to when the object has 

 been merely the preparation oFleucine and tyrosine, for these two 

 bodies are, with few exceptions, obtained together, and have to be 

 separated one from the other. 



As a raw material for preparing leucine the following, amongst 

 other substances, have been chiefly employed : meat, cheese, fibrin, 

 horn, wool, feathers, yellow elastic tissue. The following are the 

 details of the method for obtaining both leucine and tyrosine from 

 horn-shavings : 



1000 grammes of horn-shavings are boiled for 24 hours with a mixture 

 containing 2500 c.c. of concentrated sulphuric acid and 6*5 litres of water, 

 the evaporated water being replaced from time to time. 



Thin milk of lime, of uniform consistency, is then gradually added to 

 the acid liquid until an alkaline reaction is obtained, the liquid being con- 

 tinually stirred. The mixture, which necessarily contains a large quantity 

 of precipitated calcium sulphate, is filtered through a jelly-bag; the residue, 

 after squeezing, is boiled with water and again filtered. The mixed filtrates 

 are slightly acidulated with oxalic acid, which precipitates the calcium 

 originally present in solution as calcium oxalate. The liquid being filtered, 

 the filtrate is concentrated until a crystalline pellicle appears, when it is set 

 aside to cool and to crystallise. 



The united masses of crystals are dissolved in boiling water ; some 

 solution of ammonia is added, and then, with continual stirring, a solu- 

 tion of lead acetate, until the precipitate which forms is no longer 

 brownish but white. The liquid is then filtered and the hot filtrate is 

 acidulated with dilute sulphuric acid, the precipitate of lead sulphat 

 which forms is separated by filtration and the filtrate allowed to cool, 

 when tyrosine separates almost completely and in a pure condition. 



The mother liquor from which the tyrosine has been filtered is then 

 treated with sulphuretted hydrogen so as to get rid of tbe lead which it 

 contains, and, having been again filtered and the excess of H 2 S expelled 

 by heat, is concentrated and boiled for a couple of minutes with freshly 

 precipitated cupric hydrate. A dark blue solution is obtained by this 

 process; this is filtered and concentrated, when it deposits sky-blue 

 warty masses of crystals as well as a precipitate having the composition 

 Cu (C 6 H 10 NH 2 O 2 ) 2 . Both the precipitate and the crystalline masses are 

 decomposed by means of sulphuretted hydrogen, the filtrate from the sul- 

 phide of copper formed is, if need be, decolourised by means of animal 

 charcoal, again filtered and sufficiently concentrated, when, on being set 



