THE PARATARTRATES 19 



handed hemihedral crystals turned to the right and the 

 left-handed ones to the left the plane of polarization, and 

 when I took equal weights of each of these kinds of crys- 

 tals the mixed solution was neutral to polarized light 

 because of the neutralization of the two equal and oppo- 

 site individual deviations." 



We can understand how in the presence of this un- 

 expected phenomenon, with its almost dazzling confirma- 

 tion of his preconceived idea, Pasteur received such a 

 shock that he quitted the laboratory, incapable of again 

 applying his eye to the polariscope. This was a clear 

 ray of sunlight coming to illuminate perspectives which 

 he had thus far examined only in shadow or half light. 

 Now that they were suddenl}^ illuminated it was not the 

 time to abandon them. 



The more so as immediately there was a harvest to be 

 reaped. In removing chemically from the right-handed 

 hemihedral crystals the tartaric acid which they con- 

 tained, he found an acid which, when compared minutely 

 with the acid of the grape, was found to be absolutely 

 identical with it. The left-handed crystals furnished 

 him furthermore a tartaric acid also identical in every 

 respect with the acid of the grape, save in one point, 

 that is that it bore on the left the hemihedral facet which 

 the first bore on the right, and that its solutions deviated 

 to the left exactly the same amount as equally concen- 

 trated solutions of the tartaric acid of the grape deviated 

 to the right. When these solutions were mixed there 

 was no deviation, and one obtained a third tartaric acid, 

 the paratartaric acid inactive by compensation. Fur- 

 thermore, this acid did not result from a juxtaposition 

 of these two constituents but from their combination, 

 for properly concentrated solutions of right-handed and 

 of left-handed tartaric acids often give off much heat 

 when mixed, and the liquid solidifies on the spot with an 



