Dr. E. J. Mills's Researches on Melting-point. 19 



Thus it is evident that trinitrotoluol prepared from the solid 

 modification of nitrotoluol is distinct both in form and melting- 

 point from the others ; it is also more difficult in making. 



It deserves to be mentioned that the melting-point of trini- 

 trotoluol appears to undergo a slight change under certain 

 conditions. Thus, a perfectly colourless specimen three years 

 old melted at 78°*76 — the number of observations being 13, 

 and the probable error 0*012. A few grammes of the 

 specimen F 2 , after exposure to light, with frequent agitation, 

 for 13 days, during which it became mustard-yellow on 

 the surfaces, melted at 78 0, 78 ; the number of observations 

 being 14, and the probable error 0*013. This result was 

 obtained after two crystallizations from naphtha and two from 

 spirit, when the substance had become brilliantly white. 



D. Toluidine Derivatives. 



Toliddine. — The modification examined is solid at the ordi- 

 nary temperature, and obtainable by the reduction of mono- 

 nitrotoluol. 



Sample H was purchased from Messrs. Hopkin and Wil- 

 liams. It was purified by conversion into oxalate, which salt 

 was thrice extracted by ether and then decomposed by potash, 

 distillation in a current of steam, and crystallization thrice 

 from naphtha and four times &c. (H 4 &c.) from alcohol. 



S was given me by Mr. Spiller. It was pressed and crys- 

 tallized twice from naphtha and four to five times (S 4 _ 5 ) from 

 alcohol. 



Gr was purchased from Dr. Schuchardt, of Grorlitz. It was 

 pressed, and crystallized twice from naphtha and three to four 

 times from alcohol (Gr 3 _ 4 ). 



The above were ascertained to be all different preparations. 



The melting-point of toluidine is difficult to observe. The 

 substance remains for some time in the pasty stage, and then 

 conducts heat very badly ; from this cause the melting-point 

 may easily be overestimated. On the other hand, when the 

 solid substance is plunged into a bath which is hotter than the 

 real melting-point, it melts with great readiness and sharp- 

 ness. Grood numbers can only be obtained with finely-pow- 

 dered material ; the capillary tubes must be introduced into 

 the bath at 4° or 5° below the melting-point; and the mercury 

 in the thermometer must rise very slowly towards the last.. 



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