of the Metallic Oxides. 115 



The molecule of lac tide, which in the state of vapour is 

 (C 3 H 4 2 ) 2 , ought in its natural state to be still more complex. 

 The boiling-point of this substance is really the temperature 

 at which the grouping (C 3 H 4 2 ) 2 >i becomes (C 3 H 4 2 ) 2 . This 

 is the logical conclusion from the molecular constitution of 

 carboxylated acids. The molecule of acetic acid must be at 

 least 



CH3.C.OH 



<A> 



CHs.C 7 . OH 



The formula CH 3 . COOH, commonly attributed to this acid, 

 only represents the product of the simplification of its mole- 

 cule under the action of a high temperature. That being so, 

 the molecule of lactic acid should be at least 



CH 3 



HO . CH . C . OH 



/\ 



o 



HO . CH .151 OH 



CH 3 



In the formation of dilactic acid and of lactide, two of such 

 molecules act on one another, and consequently the molecule 

 of lactide ought to be at least [(C 3 H 4 2 ) 2 ] 2 ,i. e. the double of its 

 molecule in the state of vapour. However that may be, the 

 hydroxides of the polyvalent radicals of mineral chemistry are 

 assimilable to the above organic hydroxides; and we may 

 therefore reasonably conclude that the hydroxyls which they 

 contain are of different value. This question may be answered 

 affirmatively and with certainty in some cases, notably that of 

 phosphoric acid. Thomsen, Berthelot, and Longuinine have 

 shown what is the real nature of this compound. 



Orthophosphoric acid, PO(OH) 3 , is a tribasic acid, but of 

 quite a different kind from citric acid, in so far as in the latter 

 the three hydroxyls are perfectly equivalent, as shown by the 

 identity of their heats of neutralization. Citric acid, as shown 

 by its formula, is equivalent to three molecules of carbonic 

 acid rolled into one. 



CH 2 — COOH 



HO . C . COOH 



CH 2 — COOH 



12 



