404 Dr. C. R. A. Wright on the Relations between 



In this case, however, experiment shows that a simple nume- 

 rical connexion very frequently exists between the values of the 

 ratios of the weights of any given pair of constituents in the two 

 instances. This same connexion is also noticeable when a pair 

 of constituents is common to two compounds, whether the other 

 constituents are severally identical in kind or not. This connexion, 

 known as the Law of Multiple Proportions, may be thus stated : 

 If w L and w% are the weights of any two of the various consti- 

 tuents which jointly form a weight 2(w) of any compound, 

 whilst w\ and w'% are the weights of the same two constituents 

 respectively which form part or the whole of a weight 2(w/) of 

 another compound, then 



m 



X -> 

 w a w' a n 



i _ w \ 



where m and n are integers comparatively rarely of value ex- 

 ceeding 6 or 8. 



This law is not of universal applicability, the whole class of 

 homogeneous substances known as solutions, and various other 

 products obtained by the coalescence of two or more components, 

 being exceptions thereto. 



7. It frequently happens that compounds of entirely different 

 properties and characters are produced by the coalescence of the 

 same components in the same relative ratios by weight in every 



case severally : i. e. the ratios — > —) — , . . . are all equal to the 



w 2 w 3 w 4 



ratios — r> —r> —r } • • • severally : in this case the compounds are 

 w'% w s w' 4 



said to be isomeric. 



Those isomeric bodies which exhibit a relation in vapour-den- 

 sity such that the vapour-densities of any given pair of isomerides 

 are different simple integral multiples of the same quantity, are 

 said to be polymeric. 



8. The numerical value of F necessarily varies with the cir- 

 cumstances under which the coalescence of the ingredients takes 

 place, such as temperature, pressure, the physical state of the 

 bodies concerned, &c : if the value of F be known under any 

 given set of conditions, that under any other conditions can be 

 readily calculated when certain thermal properties of the sub- 

 stances concerned are known. Thus, let the affinity between x 

 gramme of a body A, and \—x gramme of another body B, in 

 one gramme of compound be F under certain conditions, say at 

 0° and 760 millims. ; it is required to find what would be the 

 affinity F' under other conditions. Let W„ W 2 , and W 3 be the total 

 amounts of energy (active, as temperature, electric state, &c. ; 

 passive or latent, as undeveloped chemical action, physical state, 



