io THE POPULAR SCIENCE MONTHLY 



hemihedral faces ; but he had found none on the racemates. Conceiving 

 that this aspect of crystals might be an index of their molecular struc- 

 ture, he reasoned that the diverse optical behaviors of solutions of tar- 

 taric and racemic acids might be explained by a structural law. On 

 fire with this new idea, he carefully examined a lot of tartrate crystals, 

 and found, as he had anticipated, that each had hemi-hedral facets. He 

 turned now to racemate crystals, expecting to find them destitute of 

 hemihedrism. Imagine his disappointment, therefore, upon finding 

 that here also each crystal distinctly displayed hemihedrism. But upon 

 laboriously going over his work again he discovered a fact that had 

 previously escaped his notice, namely, that the half-form facets of tar- 

 taric acid were all turned toward the right while those of the racemates 

 were half right-handed and half left-handed. A new idea flashed into 

 his mind. Carefully picking apart the two kinds of racemate crystals, 

 he made a solution of each and, with anxious mind and throbbing heart, 

 applied the polariscope. The solution of right-handed crystals deflected 

 the beam to the right. They were pure tartaric acid. The solution of 

 left-handed crystals deflected the beam to the left. They were a now 

 acid — Icevo tartaric acid. He mixed his solutions in equal proportions. 

 The mixture did not affect the beam. It was racemic acid. 



His excitement was so great that he could not look through the in- 

 strument again. Like Archimedes, he exclaimed " I have found it," 

 and rushed into the corridor, where he met an assistant whom he em- 

 braced in a transport of joy. 



This was one of the most illuminating discoveries known to the his- 

 tory of chemistry up to that time. Measured by its ultimate results, it 

 is doubtless the most far-reaching discovery ever made. Developing in 

 one direction, it was the germ of a new science — stereo-chemistry; in 

 another it transformed medicine and agriculture from empirical prac- 

 tises into true sciences; and incidentally it enriched the world by a 

 number of other discoveries of unparalleled practical value. Done at 

 the age of twenty-five, this first great work of Pasteur's was a prophecy 

 of that brilliant career throughout which he continued to manifest the 

 same marvelous capacity for seeing the unseeable. It led to his ap- 

 pointment at once as professor of chemistry in the college of Dijon. 



Finding that the duties of this position consumed all his time in 

 teaching, he asked the government for a transfer to some place which 

 would admit of his going on with research. Quite unexpectedly to him- 

 self, he was sent at the beginning of 1849 to the University of Stras- 

 burg to relieve Bersoz, professor of chemistry there, who desired to go 

 to Paris. 



Eealizing fully the value of the vein he had discovered in tartaric 

 acids, he directed his energies along that line. He had found out what 

 para-tartaric, or racemic, acid is; but neither he nor any one else knew 



