COMBINATIONS BETWEEN ACTIVE MOLECULES 39 



IX 



COMBINATIONS BETWEEN ACTIVE MOLECULES 



If the ideas which we have just developed have served 

 as a foundation for stereo-chemistry, others in the same 

 group will lead us to the study of fermentations, that is 

 to say, to one of the most beautiful conquests of this cen- 

 tury of marvels. For this, let us go back to the study 

 of the tartrates. We have seen that any left-handed 

 tartrate is the twin brother of the corresponding right- 

 handed one. Save that they bear their hemihedral facets 

 in different ways, when they have them, and that they 

 have equal rotary powers but in opposite directions, the 

 two brothers are exactly alike not only in respect to their 

 geometrical form, solubility, density, etc., but also in 

 what one might call the physiognomy of the crystals. 

 These twin crystals are equally limpid or clouded, hard 

 or fragile, polished or striated; they have the same 

 internal fissures, in short, they cannot be distinguished 

 unless one subjects them to a very careful examination. 

 We have taken exact note of these resemblances in orde; 

 to convince ourselves that the molecules of these crystals 

 are identical in everything save their atomic arrange- 

 ment. The moment has come to consider this resem- 

 blance from another point of view. 



Up to this time it has been manifest to us only in the 

 combinations of the right and left tartaric acids, with 

 certain mineral substances: potash, soda, ammonia. 

 Inactive on polarized light, as the minerals are, these 

 substances are content, so to speak, with diluting the 

 active power of the tartaric acid on entering into combi- 

 nation with it. But what happens if one combines these 

 tartaric acids with active substances? If the latter, as 

 is probable, maintain their power in the compound, this 



