SODIUM CHLORIDE BERTHOLLET'S LAWS 



differs in that it proceeds slowly at the ordinary temperature, extend- 

 ing over whole years, and is not complete that is, it has a distinct 

 limit determined by a reverse reaction ; thus an ethereal salt RX with 

 water gives an alcohol ROH and an acid HX up to that limit 

 generally corresponding with two-thirds of the alcohol taken, if the 

 action proceed between molecular quantities of alcohol and acid. Thus 

 common alcohol, C 2 H 5 OH, with acetic acid, HC 2 H 3 2 , gives the follow- 

 ing system rapidly when heated, or slowly at the ordinary temperature, 

 ROH + HX + 2RX -f 2H 2 0, whether we start from 3RHO + 3HX 

 or from 3RX + 3H 2 O. The process and completion of the reaction in 

 this instance are very easily observed, because the quantity of free 

 acid is easily determined from the amount of alkali requisite for its 

 saturation, as neither alcohol nor ethereal salt acts on litmus or 

 other reagent for acids. Under the influence of an increased mass 

 of alcohol the reaction proceeds further. If two molecules of alcohol, 

 RHO, be taken for every one molecule of acetic acid, HX, then instead 

 of 66 p.c., 83 p.c. of the acid passes into ethereal salt, and with fifty 

 molecules of RHO nearly all the acid is etherised. The researches of 

 Menschutkin in their details touched on many important aspects of the 

 same subject, such as the influence of the composition of the alcohol 

 and acid on the limit and rate of exchange but these, as well as other 

 details, must be looked for in special treatises on organic and theoretical 

 chemistry. In any case the study of etheriti cation has supplied chemical 

 mechanics with clear and valuable data, which directly confirm the 

 two fundamental propositions of Berthollet ; the influence of mass, 

 and the limit of reaction that is, the equilibrium between opposite 

 reactions. The study of numerous instances of dissociation which we 

 have already touched on, and shall again meet with on several 

 occasions, gave the same results. With respect to double saline 

 decompositions, it is also necessary to mention the researches of 

 Wiedemann on the decomposing action of a mass of water on the 

 ferric salts, which could be determined by measuring the magnetism 

 of the solutions, because the ferric oxide (soluble colloid) set free by 

 the water is less magnetic than the ferric salts. 



A very important epoch in the history of Berthollet's doctrine was 

 attained when, in 1867, the Norwegian chemists, Guldberg and Waage, 

 expressed it as an algebraical formula They defined the active mass 

 as the number of molecules contained in a given volume, and assumed, 

 as follows from the spirit of Berthollet's teaching, that the action be- 

 tween the substances was equal to the product of the masses of the 

 reacting substances. Hence if the salts MX and NY be taken in 

 equivalent quantities (m = 1 and n = 1) and the salts MY and NX are 



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