CHAP. III.] PHYSICAL AND CHEMICAL PROPERTIES OF LEUCINE. 239 



O OH 



C 4 H 9 cf +NH' 3 = C 4 H 9 CH / 

 \ \ 



_H NH 2 



Valeraldehyde Valeraldehyde-ammonia. 



This compound is now collected on a filter, washed with water and 

 then boiled with a mixture of strong HCN and dilute HOI, in a flask 

 provided with an inverted condenser, until the crystals are com- 

 pletely dissolved. (Two parts of valeraldehyde-ammonia are boiled 

 with 1 part of HCN and an excess of dilute HC1.) It appears that 

 in the first instance a body having the formula C 18 H 33 N 5 is formed. 

 This body however splits up according to the following equation : 



C 18 H 33 N 5 + 6H 2 = 3 (C 6 H 13 N0 2 ) + 2NH 3 . 

 Leucine 



The contents of the flask are now concentrated on the water bath 

 in a draught chamber, due precautions being taken now (as well 

 as in the previous operation) against the possible inhalation of the 

 poisonous vapour of hydrocyanic acid which is evolved abundantly. 

 When the liquid has cooled, ammonia is added, when part of the 

 leucine separates out and is collected on a filter. The mother liquor 

 is evaporated to dryness, the residue extracted with, dilute hydro- 

 chloric acid, and the solution having been concentrated on the water 

 bath is again treated with ammonia 1 . 



Physical and Chemical Properties of Leitcine. 



Crystalline Pure leucine presents a snow-white appearance 



form and melt- and occurs in the form of colourless and light crys- 

 talline doubly refracting plates, possessed of a greasy 

 feel and which float on water without being wetted. 



When heated to 170 C., leucine melts and then gives off fumes 

 which condense in the cooler part of the tube forming an ex- 

 ceedingly light sublimate, which has been compared to the so-called 

 ' Philosopher's wool,' i.e. sublimed zinc oxide. 



When the sublimed leucine is examined microscopically it 

 presents the appearance of thin plates grouped into rosette-shaped 

 masses ; the plates when seen edgeways appear to the observer as 



needles. 



When leucine separates from solutions which contain other sub- 

 stances it usually forms crusts which under the microscope are seen 



1 Parkinson, Ann. Ch. u. Pharm., Vol. xc. p. 144. Limpricht, Ibid. Vol. xciv. 

 p. 243. 



