184 Mr. M. M. Pattison Muir on 



and by substituting these values in the equation of equilibrium 

 and multiplying by V 2 , we get the general equation 



(P-jr)(Q-*)-J(F' + *XQ' + *)" 



Those reactions which consist of two parts, the direct and 

 the reverse chemical change, are most favourable for the study 

 of the influence of mass. As examples of this class of changes 

 may be cited: — the oxidation of a metal by water-gas, and the 

 reduction of the metallic oxide so produced by hydrogen; 

 the dissociation of a substance A B under conditions such that 

 A B and A and B (the products of the dissociation) are simul- 

 taneously present in the chemical system ; the division of two 

 acids between two bases so as to produce a soluble and an inso- 

 luble salt ; and the mutual decomposition of two soluble com- 

 pounds with the production of substances themselves soluble 

 under the experimental conditions. 



In their earlier paper Guldberg and Waage give the results 

 of a long and elaborate series of experiments upon the action 

 of carbonates of the alkalis on barium sulphate, and of alkali 

 sulphates upon barium carbonate ; they also consider the results 

 obtained by Berthelot and St. Giles in their examination of 

 the reaction between alcohol and acetic acid, which results in 

 the production of acetic ether and water. From these, and 

 other quantitative results, the law of mass-action already stated 

 was deduced. 



In their later paper the same naturalists detail the results 

 of their examination of many different reactions, and show 

 that in each case the law of mass-action holds good. 



Guldberg and Waage recognize two main groups of chemi- 

 cal forces : — the true forces of affinity r , which bring about the 

 formation of new chemical substances; and the secondary forces, 

 the action of which is to be traced to the presence of foreign 

 bodies, i. e. bodies other than those directly undergoing che- 

 mical change. 



Guldberg and Waage do not think that a complete account 

 of a chemical change involving simultaneous series of decom- 

 positions and recompositions can be given, if regard be paid 

 merely to the forces of attraction at work between the sub- 

 stances, or the constituents of the substances, upon which the 

 change is effected ; they deem it necessary to consider the mo- 

 lecular and atomic movements of these substances. 



The equilibrium attained by a system in which the changes 



A + B = A' + B ; , A' + B' = A + B 

 have been allowed to proceed is regarded by them as by no 



