S. p. ^Sadder — Occurrence of Tartronic Acid. 115 



In one or two of these cases, however, there is still a dijffer- 

 ence of opinion as to whether the acid named is the one possess- 

 ing the normal molecular structure given above, or is only an 

 isomer of it, having its carbon atoms differently united. Nota- 

 bly with glyceric acid is this yet an open question. Some 

 results lately obtained in the course of a study of this acid 

 appear to me to be of value for the solution of this question. 



The other view of the molecular structure of glyceric acid 

 makes it unsymmetrical, two of the carbon atoms being doubly 

 united. The formula given is 



As will be seen, this formula does not contain the carboxyl 

 group, hitherto supposed to be the inevitable characteristic of 

 an organic acid. The author of this theory is Prof. Wislicenus, 

 of Wiirzburg, and the following are the reasons given in sup- 

 port of it. If lactic acid be acted upon with hydrogen iodide, 

 a iodo-propionic acid is formed, according to the following 



6h.0H+HI=CH.I -fH.OH 



C.OOH CO. OH. 



This when heated to 150° with strong HI is changed into 



propionic acid. If, on the other hand, glyceric acid be acted 



upon with hydrogen iodide, p iodo-propionic acid is formed. 



If this had the formula 



CHJ 

 6h, 



silver oxide, it would pass into < 

 I not, however, do this, but a new 

 ictic acid is formed — hydracrylic- 



That the molecular structure of this acid is essentially dif- 

 ferent from that of ethylene lactic acid is proved by the oxy- 

 dation products of the two. Ethylene lactic acid yields malonic 

 acid, while hydracrylic does not'yield a trace of this, breaking 

 up into glj^colic and oxalic acids and carbonic dioxide. More- 

 over, hydracrylic acid on heating yields acrylic acid, a deriva- 

 tive of allyl alcohol, instead of the lactid yielded by the lactic 

 acids. 



