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



the forms of matter A x , A 2 , A 3 , . . . ; which are also said to unite 

 or combine , forming the compound, or to be constituents or compo- 

 nents of the compound. 



These components are said to be united by the force of che- 

 mical affinity } or, more briefly, by the force of affinity. 



This force is measured by the work gained during the coales- 

 cence. If W absolute units of work are gained during the for- 

 mation of the weight ~%{w) of the compound, the affinity of the 



W 



constituents A v A 2 , A 3 , ... in the compound is said to be — f , 



or F per unit of weight : — the value of F being positive when W 

 is positive, *. e. when work is gained during the formation of the 

 compound from its constituents ; and negative when W is nega- 

 tive, i. e. when work is spent during the coalescence of the con- 

 stituents. 



For convenience, the absolute unit of affinity (when one ab- 

 solute work-unit is gained during the formation of a unit of 

 weight of compound) is not employed in the subsequent calcula- 

 tions, a subsidiary affinity-unit being used instead, viz. when one 

 calory is produced during the formation of a unit of weight of 

 compound : the relation between the absolute work-unit and the 

 calory is given by the equation 



W=Cx 0-00024054, 

 or 



C = Wx 4157-25, 



where W and C indicate the same amount of work in absolute 

 work-units and calories respectively — the calory being equal to 

 the quantity of heat required to raise the temperature of one 

 gramme of water at maximum density 1 degree Centigrade, and 

 being equal to 423*542 metre-grammes at Manchester, or 

 4157*25 absolute work-units, g being 9*8155 at Manchester. 



Hence the affinity is positive when heat is evolved during the 

 coalescence of the constituents, and negative when heat is ab- 

 sorbed during the process. 



3. Conversely, when a weight %{w) of a homogeneous body 

 can be split up into weights w lt w^, w 3 , ... of dissimilar sub- 

 stances, W work-units being spent during the change, the result- 

 ing substances are said to be components of the compound, and 



W 



their affinity in the compound is ^ , per unit of weight. 



4. A substance is also said to consist of such and such con- 

 stituents when, although the so-called compound is not directly 

 obtainable by the coalescence of the constituents, nor can it give 

 rise by splitting up to these constituents, it is nevertheless re- 

 lated to these constituents in the same way that veritable com- 



