DR A. CRUM BROWN ON ISOMERIC COMPOUNDS. 71 i 



by the water residue ; but we have two varieties of malic acid, active and 

 inactive ; these must therefore be absolutely isomeric. 



9. The same argument applies to the case of active and inactive aspartic 

 acids ; aspartic acid being succinic acid in which one atom of radical hydrogen 

 has been replaced by the ammonia residue NH2. 



10. As there are two possible formulae for bibromo-succinic acid, there are 

 also two for tartaric, or dioxy-succinic acid. We have not the same reason for 

 excluding either of these in this case as in that of the bibrominated acids ;* 

 but as we have three undoubtedly different varieties of tartaric acid (excluding 

 racemic acid), two of these at least must have one of these formulae in common. 



So far we have been concerned with pairs of substances which seem to be really 

 absolutely isomeric. The remaining substances in our list are more probably 

 metameric. 



11. If we consider the various reactions of the ethylene compounds, particu- 

 larly the formation of gly collie acid from glycol, we are forced to the conclusion 

 that the two unsaturated equivalents of the radical ethylene belong to two 

 different carbon atoms. This conclusion may also be arrived at in another, 

 perhaps less satisfactory way. As chloride of ethylene is formed by the direct 

 union of chlorine and ethylene, the chlorine must be combined with those carbon 

 equivalents which in ethylene gas are combined with one another ; but equivalents 

 of the same atom cannot be combined with one another, therefore in chloride of 

 ethylene the two atoms of chlorine must be combined with different carbon 

 atoms. The constitutional formula of chloride of ethylene is therefore 



© © 



1 I 



©--(J>-(^-© 



(b (b 



and that of oxide of ethylene 



©--(e>^-© 



^r:^^ 



Again, the reactions of aldehyde, the oxide of ethylidene, lead to the view of its con- 

 stitution first proposed by Kolbe, and now almost universally adopted, jj^ V CO, 



* It would be interesting to compare the properties of the tartaric acid formed from isobibromo- 

 succinic acid with that from bibromo-succinic, and with the varieties obtained from the grape. 



VOL. XXIII. PART III. 9 E 



