OF ARTS AND SCIENCES. 



83 



crystallization suggested to us that the substance probably occurred in 

 two modifications, which was proved to be the case by the determina- 

 tion of the melting points of the two sorts of crystals, the yellow, after 

 thorough purification, melting at about 122°, the red at 143°. As the 

 substance passes from one form to the other with great ease, many ex- 

 periments were necessary in order to find methods for obtaining each 

 in a state of purity. 



Red Modljication of Anilidotrinitrophenyltartronic Ester. 



To obtain this form from the crude product of the reaction it was 

 crystallized several times from alcohol, until a mixture of the two forms 

 rich in the red had been obtained, and then a strong alcoholic solution 

 of the mixed crystals was allowed to evaporate slowly at temperatures 

 from 50° to 70°. The product thus obtained, which showed no sign 

 of the yellow form, was dried at 100°, and analyzed with the following 

 results : — 



I. 0.1792 gr. of the substance gave on combustion 0.3114 gr. of car- 

 bonic dioxide and 0.0694 gr. of water. 

 II. 0.2016 gr. of the substance gave on combustion 0.3534 gr. of 

 carbonic dioxide and 0.0809 gr. of water. 

 III. 0.1938 gr. of the substance gave 19.9 c. c. of nitrogen at a tem- 

 perature of 22° and a pressure of 767.7 mm. 



III. 



11.76 



The air-dried red crystals lost only 0.19 per cent when dried at 100°, 

 and therefore were free from water or alcohol of crystallization. 



Properties. — The red form of anilidotrinitrophenyltartronic ester 

 crystallizes in well formed prisms, often half a centimeter long, with 

 at each end a pyramidal termination consisting of four planes. It has 

 an orange-red color like that of potassic dlchromate, and melts at 

 143° ; is essentially Insoluble in cold water, very slightly soluble in 

 boiling water, forming a pale yellowish solution ; soluble in cold al- 

 cohol, rather freely in hot. This solution if allowed to evaporate at 

 temperatures from 50° to 70° deposits crystals of the red modification, 

 as has been already stated ; but if allowed to evaporate at ordinary 

 temperatures, a mixture of red and yellow crystals is usually obtained, 

 although occasionally only red crystals are formed under these con- 



