CHLORIDE BERTHOLLET'S LAWS 429 



At the beginning of the year I860, the doctrine of the limit of 

 reaction and of the influence of mass on the process of chemical trans- 

 formations received a very important support in the researches of 

 Berthelot and P. de Saint-Gilles on the formation of the ethereal salts 

 RX from the alcohols ROH and acids HX, when water is also formed. 

 This conversion is essentially very similar to the formation of salts, but 

 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 O 2 , gives the follow- 

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

 ROH + HX + 2RX + 2H 2 O, whether we start from 3RHO+3HX or 

 from 3RX + 3H 2 0. The process and completion of the reaction in the 

 above-described 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 and 

 other reagents 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., 85 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 essential 

 aspects of the same subject, such as the influences 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 etherincation 

 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 which we shall yet meet with 

 on several occasions, gave the same results. With respect to double 

 saline decompositions, it is necessary to further mention the researches 

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

 ferric salts, which could be judged of 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, Guldbergand Waage, 



