24 Mr. E. G. Young. On the Optical Rotatory 



In the light of the above discussion it is of interest to consider the 

 conditions under which Hofmeister first obtained crystals. He slowly con- 

 centrated a half-saturated solution of ammonium sulphate containing albumin. 

 Now, such a solution is naturally acid, due to the fact that (NH 4 ) 2 S04 is a 

 salt formed by the union of a very strong acid with only a moderately strong 

 base. Furthermore, on slow evaporation in open vessels some of this free 

 NH4OH will be lost, and the solution will become more acid until such a 

 point is reached at which the hydrolysis will become negligible. It would 

 thus be conceivable that at one stage of evaporation globuliths would appear, 

 and, at a later stage, when the solution had become more acid, crystals. The 

 globuliths might then take up more acid and crystallise, since the phases 

 differ in degree of their constituents and not in kind, and the disperse phase 

 is more or less permeable to electrolytes in the continuous one. 



In any case, both crystals and globuliths are precipitated again from a 

 solution of (NH4) 2 S04, which is much less concentrated than that required for 

 ordinary amorphous material. The concentration of (NEL^SC^ is usually 

 slightly more than quarter saturation, while amorphous albumin in equal 

 concentration requires considerably more than half saturation. This fact in 

 itself, to my mind, is a very good reason for believing that both crystals and 

 globuliths are hydrates of ovalbumin. The rdle of (NEU^SCU would thus be to 

 remove the solvate water associated with the albumin molecular aggregates 

 which kept them in solution, but to leave the hydrate water still attached. 

 If the hydrate were not formed, then the concentration would have to be con- 

 siderably increased in order to control this excess of free-water molecules, 

 and an amorphous precipitate would result. 



Discussion of Results. 



From the experiments described in the preceding sections we have seen 

 that there is a variation of the specific rotation of ovalbumin, depending upon 

 the hydrogen ion concentration of the solution. The addition of acid to a 

 solution at its isoelectric point causes an increase of its rotatory power, 

 which remains constant. The addition of alkali to a similar solution causes 

 a prompt fall in rotatory power, which slowly rises to the original value. 

 Further addition of alkali has no effect. These changes are reversible from 

 either side of the isoelectric point. If, however, the albumin sample be kept 

 at the isoelectric point or thereabouts, without adding either acid or alkali, it 

 is possible to obtain a constant specific rotation for successive recrystallisations. 



The maximum experimental errors are small. The polarimeter readings 

 are accurate to O'Ol of a degree, and since rotations of ten degrees or more 

 have been observed, the error from this determination would not be greater 



