CHEMICAL BASIS OF THE. ANIMAL BODY. 1 !'. 



of the accompanying tyrosin is removed. The filtrate is now 

 further concentrated, treated with excess of hot alcohol, which 

 precipitates the peptones, and filtered while hot. If much leucin 

 is present ;i lari;e part of it crystallises out on cooling the aleo- 

 holir filtrate, ami tin- rest on concentrating by slow evaporation. 

 There is a large loss of leucin by both the above methods, and 

 the resulting product is far from pure. To obtain pure leucin 

 it should be synthetised by the action of ammonia on a-brom- 

 caproic acid. 1 



M an approximately quantitative separation of leucin from solu- 

 tions when- it is mixed with "ther substance.-, e. g. an extract of tis- 

 siie-, or a digestive mixture, is a matter of great difficult v. Advantage 

 may in smut- ease> In- taken of its behaviour toward > hydrated oxide of 

 copper, with which it forms a compound. - 



For ordinary practical purposes the microscopic appearance of 

 the crystals affords tin- must convenient means for recognising 

 leucin, and in this way very minute traces may be determined 

 with certainty. The confirmation of the clue thus afforded by 

 tin- application of chemical tests is however not easy unless a 

 tail amount of material is at hand, and that in a pure condition. 

 In the latter case the following tests may be applied, (i) When 

 'i illy heated to 170 leucin sublimes and yields a charac- 

 teristic odour of amylamin The only other substance of physio- 

 logical importance ordinarily met with which yields a sublimate 

 on heating is hippuric acid, due to its decomposition and the sub- 

 limation of the benzole acid thus set free, (ii) sv// <//'.-< /.>/. 

 < >nly applicable to very pure leucin. The suspected substance is 

 evaporated carefully to dryneu with nitric acid on the lid of a 

 platinum crucible; the residue, if it is leucin, will be almost 

 transparent ami turn yellow or brown on the addition of caustic 

 soda. If this be again very carefully concentrated with the al- 

 kali an oily drop is obtained, which runs over the platinum in a 

 -pheroidal state. 



The optical properties of leucin have not as yet been fully 

 worked out. Experiment shows that its solutions are sometimes 

 optically active, at other times inactive, dependently upon the 

 source and mode of formation of the leuein. This corresponds 

 to the expectations as to its optical behaviour based, in ac- 

 ordance with the Van't HoH-I.e I'.el hypothesis, upon its con 

 Mitutional formula.' 



The possible relationship of leucin to the formation of urea in 



1 IIufli.T. .In f.i>r,,kt. ('htm. (2) Bd. I. (1- 



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Bd. x. (188C,), S i:u 



