1881.] 



On Melting Point. 



205 



Substance. 



Weighted, 

 mean. 



After 

 Poggendorff's 

 correction. 



Air therm. 





42 -765 



42 '700 



42 



890 





44 -270 



44 -205 



44 



392 





51*305 



51 -239 



51 



407 





52 723 



52-657 



52 



821 





56 '175 



56 -110 



56 



261 



Dinitrophenol (a) .... 



61 -778 



61 -714 



61 



843 





61 -806 



61 -742 



61 



871 





69-211 



69 -154 



69 



•252 



. (*) 



69 -571 



69 -514 



69 



•610 



69 -667 



69 -610 



69 



•706 



Dinitrobromobenzal. . . 



70-598 



70-542 



70 



•634 





77-052 



77 -004 



77 



•068 





78 -821 



78 -776 



78 



833 





78 -841 



78 -796 



78 



odd 



Trinitrotoluol (M) .... 



80 -061 



80-018 



80 



•070 



80 -524 



80-481 



80 



•532 



Nitrodibromobenzol. . . 



83 -490 



83 -452 



83 



•492 





87 -037 



87 -007 



87 



•035 









89 



•712 





111 -413 



111 -448 



111 



•455 



Dinitrophenol (b) .... 



111-579 



111 -614 



111 



•621 





116 -247 



116 -298 



116 



•319 





121 -082 



121 -151 



121 



•194 



Mean probable error of a result, in terms of the air thermometer, 

 0°-015. 



The method of purification adopted was based upon what may be 

 termed the principle of multiple successive solvents. It is well known 

 that small quantities of impurities are prone to cling to substances 

 with great tenacity ; but the observation has most frequently been 

 made in connexion with a single solvent. One can readily conceive 

 that the tenacity with which a given trace of a foreign body is held, 

 under such circumstances, may be in effect constant. If, however, we 

 now transfer the mixture to a second solvent, it may be presumed that 

 the trace will be in a condition of altered adhesiveness, and may be 

 much more readily separable. In accordance with this principle the 

 substances were crystallised from two solvents at least, and the 

 constant melting points of successive fractions recorded. After every 

 fractional crystallisation, pressure was had recourse to for about 

 twelve hours. 



A glance at the table shows that, on the whole, melting point and 

 formula grow together. The following instances of this law 

 ,(M.P.=m Formula) are adduced: — 



