174 Dr. E. J. Mills on Melting-point and 



practical chemistry, it being well known not only that heat 

 may modify the rate of a given chemical change, but may 

 altogether alter the character of the change, and produce the 

 same effect as the presence, in the system of reacting sub- 

 stances, of a certain reacting substance. 



3. The most general law known to me of chemical change, 

 considered with respect to the mass of the reagents, is, that 

 chemical effect is dwectly proportional to the product of the active 

 masses, and inversely proportional to the sum of their residues. 

 This law has been expressed* in the equation 



__ a • x y 



where a is a factor depending on the conditions of the expe- 

 riment. 



In order to adjust this equation to meet the case of melting- 

 point and boiling-point as related to chemical composition, we 

 have to suppose that a practically inexhaustible means of 

 raising temperature has been placed at our disposal. On the 

 other hand, the series to be considered in this memoir have 

 all the general formula pX. . «#CH 2 . The application of heat 

 to the members of these series has for its effect the event 

 which is measured as a melting-point or boiling-point. If t be 

 the number of degrees 0. corresponding to CH 2 , /? a constant 

 of condition, and y the resulting effect thus measured, 



fit* 



y— 



Inasmuch, however, as x is in any given case necessarily 

 constant and = x n and the difference between t and t r is a 

 negligibly small quantity, the equation may be written, 



fitx 



x + t 



or, dividing numerator and denominator by t and using a new 

 constant, 



fix 



y = -Jz. . 



1 + yx 



The origin of most organic series is an ideal quantity, such 

 as H 2 0, H 2 , C, &c, which in the mathematical representa- 

 tion of melting-point or boiling-point requires the insertion of 

 a new constant, linearly modifying x. The complete equation 

 thus becomes 



* For the first enunciation of this law and instances of its numerical 

 verification, see Chem. Soc. Journ. 1878, i. p. 307; 1879, i. p. 336; 1881, 

 i. p. 533 ; 1882, i. p. 18. 





