OF ARTS AND SCIENCES. 131 



II. On tue Crystalline Form of a Diciiloracrylic Acid. 



By W. H. Melville. 

 (Communicated by II. B. Hill.) 



Although the physical properties of the ^ dichloracrylic acid of 

 Wallach * are decidedly different from those which W, Z. Bennett 

 and I found to be characteristic of the dichloracrylic acid made from 

 mucochloric acid,t a difference which appeared to be fully confirmed 

 by a. comparison of the salts of the two acids, still it seemed to me 

 desirable to prove with a little more precision the difference between 

 the two. Since Wallach had made no determinations of the solubility 

 of his acid or its salts, and moreover thought % that little weight 

 should be attached to the determinations of crystal-water which he 

 had as yet published, there remained no definite, well-established 

 points of difference except the melting-points (86° and 77°) and a 

 difference in the crystalline form of the potassium salt : one crystal- 

 lizing in needles, the other in hexagonal plates. Since the & acid had 

 been obtained in measurable crystals and fully described in Wallach's 

 first paper, although we had previously been unable to get measurable 

 crystals of our acid, I made fresh attempts with larger quantities of 

 material than had then been at our disposal. I found that by the 

 slow cooling of a warm, moderately dilute solution in chloroform well- 

 developed crystals could be obtained, although the determination of 

 the crystals was rendered difficult on account of the rapid roughening 

 of their faces when exposed to the air. Dr. "W. H. Melville succeeded, 

 however, in making the necessary measurements, and to his kindness 

 I am indebted for the following description. The purity of the 

 material used was determined by analysis. 



0.2061 grm. of the substance gave 0.4198 grm. AgCl. 



Calculated for C3H.2CI.2O2 . Found. 



CI. 50.36 .50.35 



* Ann. Cliem. u. Pharm. vol. cxciii. 19. 



t Tliese Proceedings, Vol. XVI. (n. s. viii.) p. 206. 



I Ann. Cheno. u. Pharm. cciii. 80. 



