Oct. 2, 1879] 



NATURE 



531 



of the acting bodies. He further took into account the 

 physical conditions under which the chemical change 

 proceeded, inasmuch as he regarded chemical decomposi- 

 tion as not completed by chemical affinity alone, but by 

 affinity aided by cohesion and elasticity. 



Upon Berthollet's view of affinity, the affinity of an 

 acid was greatest for that base with which it combined in 

 smallest quantity ; and a substance with very small affinity 

 for the constituents of another was nevertheless capable 

 of decomposing that other, provided a sufficiently large 

 mass of the first was employed. 



No important general theory of chemical affinity has 

 been propounded since the time of Berthollet ; chemists 

 have now favoured his views, now the views of Bergmann, 

 the preponderance of opinion inclining generally towards 

 the theory of the French chemist. 



In the year 1867 a most important paper, "Etudes sur 

 les Affinitds chimiques," was published in Christiania by 

 Professors Guldberg and Waage. This paper has been 

 supplemented by a second communication within the last 

 few months by the same authors : the general theory of 

 chemical affinity has been also materially advanced by 

 three publications made by W. Ostwald, ranging from 

 1877 to the present year, and entitled " Volumchemischen 

 Studien." 



These papers undoubtedly mark an epoch in the deve- 

 lopment of chemical theory, presenting, as they do, the 

 beginnings of the application of mathematical reasoning 

 to the facts of chemistry, and furnishing, likewise, new 

 methods for solving some of the more intricate problems 

 presented to the chemist. 



Guldberg and Waage consider specially the influence of 

 mass upon chemical action. In the general equation 

 A -\- B = A' -\- B', where A' and IT represent the new 

 substances formed by the mutual actions of A and B, we 

 have two forces at work, that causing the formation of 

 A' and />", and that tending to re-fomi A and B ; for any 

 given stable condition of the system A, B, A', B , these 

 two forces are in equilibrium. The force causing the 

 formation of AJ and B' increases proportionately to the 

 coefficient of affinity of the reaction, and is also depen- 

 dent upon the quantities of A and B present. If the 

 active masses of A and B (that is, the masses of these 

 bodies present in unit volume of the reacting system) be 

 denoted by p and q respectively, and the coefficient of 

 affinity by k, then the force is represented by the expres- 

 sion kpg. 



This expression may also be regarded as representing 

 the amounts of A and B, transformed, in unit time, into 

 A' and If. 



By a similar method the expression 1^ p q' \% arrived 

 at as representing the force which tends to bring about 

 the reformation of A and B. The condition of equilibrium 

 of the system is such that k p q = k! p' q'. 



\{ pqp' q' be experimentally determined, the proportion 

 h : k' can be calculated, and hence the limit of the reaction 

 for each initial condition can be determined. 



GuldbergandWaagehavc applied their law of massaction 

 to a number of special cases of chemical decomposition, the 

 more important of which are decomposition of carbonates 

 of the alkalis by barium sulphate, and the reverse action, 

 formation of ethylic acetate and water by the action of 

 alcohol upon acetic acid, division of a base between two 

 acids, decomposition of hydriodic acid in presence of an 

 excess of either iodine or hydrogen, &c. 



Those actions which consist of two parts — the direct 

 and the reverse chemical change — are especially adapted 

 for the study of the influence of mass. This class of 

 action is regarded by Guldberg and Waage as complete, 

 while those in which — by the removal from the sphere of 

 action of one of the products of the first part of the change 

 or by other means — the reverse action is not accomplished, 

 arc regarded as incomplete. The combination of hydrogen 

 and oxygen, for instance, to form water, is but one phase 



of the complete action, the other phase of which is the 

 decomposition of water into hydrogen and oxygen ; by 

 conducting the first part of this action at a temperature 

 above that of the dissociation temperature of water, the 

 action becomes complete. 



In their view of chemical action, Guldberg and Waage 

 regard the molecules of the reacting substances A and 

 B as composed of the atoms a y, and /3 8 respectively ; 

 these atoms are supposed to perfomi their own vibratory 

 movements within the respective molecules. At certain 

 points the force acting between a and y and between jS 

 and S is supposed to be very small ; if, when a and y are 

 in this position, the molecule B come near \.o A, an 

 exceedingly small disturbing influence may determine 

 that a and /3 and y and 8 pair off together, to form the 

 new molecules A' and S . A similar view is taken of the 

 reverse action whereby A and B are reformed. 



Guldberg and Waage consider in detail only the action 

 of mass as influencing the force of chemical affinity, but 

 they also recognise the existence of secondary forces due 

 to the foreign bodies present, i.e., bodies which do not 

 directly undergo chemical change during the reaction 

 under consideration. Among these foreign bodies is to be 

 placed the liquid in which the salts are dissolved whose 

 mutual action is to be studied. 



That the degree of dilution of the reacting liquids 

 exerts an influence upon the course of a chemical change 

 is witnessed to by many well known facts. Quantita- 

 tive measurements of this influence are not, however, 

 numerous. 



If a molecular explanation of chemical action be 

 adopted, we should expect to find a marked difference 

 between the modifying influence of physical conditions 

 upon a chemical change occurring in a dilute and the 

 same change occurring in a more concentrated solution. 



In the former case, where the molecules of the reacting 

 bodies are comparatively widely separated from one 

 another by those of the diluent, and where possibly a larger 

 amount of energy of motion is associated with each mole- 

 cule, one might expect that small disturbing influences 

 would produce a marked effect upon the course of the 

 chemical change. And such an effect is produced by 

 small changes in physical conditions. 



As one result of experiments in which I have been 

 engaged for some time, I find that when a dilute solution 

 of strontium chloride is mixed with a dilute solution of 

 sulphuric acid (the molecular proportions being as i : 3 

 or 1 : 4), the amount of strontium sulphate produced in a 

 short time — thirty to sixty minutes — is very largely de- 

 pendent upon such conditions as the manner in which the 

 two liquids are mixed, the smoothness or roughness of 

 the vessel containing the solutions, &c., &c. Similar 

 results have been obtained in measuring the reaction 

 between barium chloride and potassium oxalate in dilute 

 solutions. 



But however a special chemical decomposition may be 

 influenced by such physical conditions as those mentioned, 

 or by such physical conditions as temperature, time, &c., 

 it seems very probable that each chemical molecule is 

 possessed of a definite coefficient of affinity. The re- 

 searches of Guldberg and Waage, as also those of Ost- 

 wald favour this view. 



The law of mass action formulated by the former 

 naturalists does not pennit of determinations being made 

 of the coefficient of affinity of any substance, but only of 

 the ratio between the coefficients of two substances. Ost- 

 wald also does not attempt to do more than determine the 

 relative affinities of substances. 



He confines himself especially to the neutralisation of 

 acids by bases ; from his results he deduces the probable 

 conclusion that the relative affinity of an acid is a fixed 

 number independent of the nature of the base acted upon, 

 and independent of temperature. The relative affinity is, 

 however, a function of the absolute affinity which is itself 



