ISOMERISM. 157 



of both formic ether and the acetate of methylene may be re- 

 presented by C 6 H 5 O 4 , the density of both their vapours is 

 2574 ; and what is very remarkable, these bodies in their ordi- 

 nary liquid state almost coincide in properties, the density of 

 formic ether being 0.916, and that of the acetate of methylene 

 0.919, (density of water being 1000), while the first boils at 

 133o, and the last at 136.4. But when acted on by alkalies, 

 their products are entirely different, the one affording formic 

 acid and alcohol, and the other acetic acid and wood-spirit. 

 Each of the isomeric bodies in question contains, indeed, two 

 different binary compounds, and their constitution is truly repre- 

 sented by different formulee ; 



Formic ether. , . . C 4 H 5 O + C 2 H O 3 

 Acetate of methylene. . C 2 H 3 O-f C 4 H 3 O 3 

 in which the same atoms are seen to be very differently ar- 

 ranged. 



The last class of isomeric bodies are of the same atomic 

 weights, but their constitution or molecular arrangement 

 being unknown, their isomerism, cannot at present be ex- 

 plained. It can scarcely be doubted, however, that their mole- 

 cular arrangement is really different. Cyanic and fulminic 

 acids are in this predicament, their common formula being 

 N C 2 O. Malic and citric acids were also believed to present a 

 similar relation, but recent discoveries respecting the constitu- 

 tion of their salts have separated these and several other acids 

 heretofore viewed as isomeric. 



One pair, however, of isomeric bodies remains which have 

 defeated every attempt at explanation, the racemic and tartaric 

 acids, which exhibit a similarity of properties, and a paralle- 

 lism in their chemical characters that are truly astonishing. 

 These acids are found together in the grape of the upper Rhine. 

 They differ considerably in solubility, the racemic being the 

 least soluble, so that they may be separated from each other by 

 crystallization ; and the racemic acid contains an atom of water 

 of crystallization, which is not found in the crystals of tartaric 

 acid. They form salts which correspond very closely in their 

 solubility and other properties. The bitartrate and biracemate 

 of potash are both sparingly soluble salts: the tartrates and 

 racemates of lime, lead and barytes are all alike insoluble. Both 

 acids form a double salt with soda and ammonia, which is an 

 unusual kind of combination. But what is most surprizing, 



