OF ARTS AND SCIENCES. 85 



in part, when heated to a few degrees below that temperature ; it is 

 necessary therefore to heat the bath up to the meltiug point before im- 

 mersing the capillary tube containing the substance ; under these con- 

 ditions it melts, and then changes to the red form, and solidifies again, 

 after which it does not melt until about 140°. The melting point we 

 ascribe to this substance is 122°, but we are not sure that this is ac- 

 curate to one degree. This change from yellow to red can also be 

 brought about slowly by heating at 100°, by boiling the yellow form 

 with water for some time, or most conveniently by crystallization from 

 alcohol at temperatures from 50° to 70°. In its solubility in the differ- 

 ent solvents the yellow form does not differ much from the red, but 

 seems in general to be more soluble. 



We have made many attempts to determine the molecular weights 

 of the two modifications by the method of Raoult, but have not as yet 

 succeeded in finding any solvent which gives satisfactory results. 

 Acetic acid, owing to its conversion of the red into the yellow form, 

 could at best give results only for the latter, but a number of deter- 

 minations showed us that it was of no use even for this purpose, as 

 results were obtained varying from 295 to 345 (the theoretical molecu- 

 lar weight is 478), therefore showing that some reaction (probably 

 the formation of an acetoxymalonic ester) had taken place between 

 the acetic acid and the ester. An experiment with phenol gave an 

 excellent result with the red form, 477 instead of 478 ; but with the 

 yellow only 307 was obtained, indicating a chemical action similar to 

 that observed with acetic acid, and we are not inclined to accept any 

 result with phenol, however excellent it may appear, as with a sub- 

 stance which is so easily affected by solution as this there can be no 

 certainty that it has remained in the same modification, unless it can 

 be recovered directly from the solution used, and this we have found 

 no means of doing in the case of phenol. Benzol gives such uncer- 

 tain results with substances containing a hydi'oxyl group,* that we did 

 not think it worth while to try it. We have hopes that naphthaline! 

 may give the desired result for the red form ; this will be tried in this 

 Laboratory, and a further attempt made to find a satisfactory solvent 

 for the yellow modification ; but as the departure of one of us from 

 Cambridge makes it necessary to postpone further work in this direc- 

 tion until next year, we have thought it best to publish at once our 

 present results, which have already reached a certain completeness. 



* Ber. d. ch. G., XXI. 707. t Ber. d. ch. G, XXII. R. 128. 



