vin COMPOSITION AND MOLECULAR WEIGHT 327 



has proved by very careful work that all albumin-crystals are crystallo- 

 graphically identical or at least isomorphic. They probably belong to 

 the hexagonal system, and are, more or less, positively doubly-refractile. 

 Egg-albumin yields principally six-sided columns, O'l to 0*15 mm. 

 long and 0'003 to 0'021 mm. thick, while serum-albumin and 

 milk-albumin show different combinations of proto-prisms and proto- 

 pyramids. In this form the crystals remain soluble for a very long 

 time, but ultimately they become denaturalised ; the crystals, as 

 Wichmann puts it, change from the monotropic a-modification into 

 the enantiotropic /^-modification ; they are changed into pseudo- 

 morphoses and lose simultaneously their optic properties. On being 

 heated in half-saturated or even stronger ammonium-sulphate solution 

 they become coagulated, and are again changed into pseudo-morphoses. 

 When quite dry they may be heated to 150 without undergoing 

 decomposition. The haemoglobin crystals are described under haemo- 

 globin. 



2. Composition, Molecular Weight, Heat of Combustion, 

 and Rotatory Power 



Albumins are not readily analysed, because their combustion is not 

 easily carried out owing to the presence of sulphur and of ash. A 

 further difficulty is one which has already been pointed out in 

 connection with the quantitative determination of the dissociation- 

 products, namely, the difficulty of obtaining uniformly pure material 

 for purposes of analysis. According to Michel, 1 serum-albumin, which 

 we may regard as a typical simple albumin, possesses the following 

 percentage composition : 



C . . . 53-08 per cent. 



H 7-10 



N 15-93 



S 1-90 



O 21-99 



It is remarkable how little other albumins differ in their percentage 

 composition from serum-albumin, notwithstanding the fact that they 

 are built up of amino-acids differing so greatly from one another both 

 qualitatively and quantitatively. 



The carbon percentage rises in casein and histone to 54 and 54'97, 

 and may fall in other albumins as low as 52 ; the nitrogen percentage 

 rises in histone* to over 1 8 and in the phyto-vitellines to over 1 9, while 



1 Michel, Wiirzburger Phys.-med. Ges. N.F. 29. 117 (1895). 



