474 UVRES D E PASTEUR 



of soda and ammonia, M. Pasteur observed that the crystals were 

 hemihedral, and of two kinds, which differed only as to right-handedness 

 and left-handedness : the one kind, which for distinction's sake may be 

 called right-handed, absolutely agreeing with the corresponding double 

 tartrate, the other with the image of the tartrate in a mirror. On 



o 



separating the crystals ol the two kinds mechanically, and dissolving them 

 apart, the solution of the right-handed crystals was found to rotate the 



I o ^ 



plane of polarization of polarized light right-handedly, like a solution of 

 the tartrate, that of the left-handed crystals left-handedly. Thse solutions 

 vielded on evaporation, the one onlv right-handed, the other only left- 

 handed crystals. The crystals of the two salts were purifed by recrystal- 

 lization, their acids isolated, and the chemical, optical, crystaljographic and 

 pyroelectric properties of the acids themselves or their salts or solutions 

 carefullv compared. A like comparison was institutcd between thse 

 acids and the well-known tartaric acid. The acid obtaincd from the right- 

 handed crystals proved.to be absolutelv identical with tartane acid in ail 

 its properties, that obtained from the left-handed crystals proved to be 

 identical, so to speak, with the image of tartaric acid in a mirror, the 

 two acids absolutelv agreeing in ail their properties except as to right- 

 handedness and left-handedness. Where the one acid vielded crystals 

 hemihedral right-handedly, the other vielded crystals similar, except that 

 they were hemihedral left-handedly ; where the one yielded a solution 

 rotating the plane of polorization right-handedly, the other yielded a solution 

 rotating it left-handedly to the very saine amount, and with the very same 

 peculiar dispersion of the colours. On mixing equal quantities of the 

 acids from the right-handed and left-handed crystals, racemic acid was 

 reproduced. 



Stimulated by this remarkable discovery, M. Pasteur lias continued his 

 labours in the same direction, and the results which be bas since obtained 

 are given in a sries of papers published in the "Annales de chimie" and 

 extending nearly to the prsent time. 



llitherto no "active" substance (i. e. one whose solution has the power 

 of rotating the plane of polarization ol polarized light) has been obtained 

 artificially from inactive substances, except in the case of the splitting up, 

 or at least sparation, of racemic acid into a right-handed and a left-handed 

 substance ; and this law seems worthy of the attention of chemists who 

 attempt the artificial formation of the organic alkaloids. This law would 

 bave been violated had two acids which chemists had obtained from fumaric 

 acid, an inactive substance, and which appeared to be identical with aspartic 

 and malic acids respectively, been really so. But M. Pasteur found that 

 thse acids were inactive, unlike aspartic and malic acids, from which they 

 also differed in some other respects. 



The two acids obtained from racemic acid were found to be identical in 

 their properties (except as to right-handedness and left-handedness) so l<>'iif 

 as they were mixed or combined with inactive substances only, but M. Pasteur 

 found that this is no longer the case when they are combined with active 

 substances, as for example the organic alkaloids, in which case the salts 

 obtained differ widely in solubility, crystalline form, etc. 



