sol>irM CHLORIDE BERTHOLI.KTS LAWS 435 



The majority of the above-mentioned researches were carried on in 

 aqueous solutions, and as water is itself a saline compound, and is 

 able to combine with salts and enter into double decomposition with 

 them, such reactions taking place in solutions in reality present very 

 complex cases. In this sense the reaction between alcohols and acids 

 is much more simple, and therefore its significance in confirmation 

 of Berthollet's doctrine is of particular importance. The only cases 

 which can be compared with these reactions from their simplicity are 

 those exchange decompositions investigated by G. G. Gustavson, and 

 which take place between CC1 4 and RBr,, on the one hand and CBr 4 

 and RC1, ( on the the other. This case is convenient for investigation 

 in the sense that the RC1,, and RBr,, taken belong (like BC1 3 , SiCl 4 , 

 TiCl 4 , POC1 3 , and SnCl 4 ) to the number of substances which are de- 

 composed by water, whilst CC1 4 and CBr 4 are not decomposed by 

 water ; and therefore, by heating, for instance, a mixture CCl 4 + SiBr 4 

 it is possible to arrive at a conclusion as to the amount of interchange 

 by treating the product with water, which decomposes the SiBr 4 left 

 unchanged and the SiCl 4 formed by the exchange, and therefore 

 by determining the composition of the product acted on by the water 

 it is possible to form a conclusion as to the amount of decomposition. 



whilst a solution of ammonia gives a contraction. The relation to water must be considered 

 ;is the cause of these phenomena. When sodium hydroxide and sulphuric acid dissolve 

 in water they develop heat and give a vigorous contraction ; the water is separated from 

 such solutions with great difficult y. After mutual saturation they form the salt Na.>SO 4 , 

 which retains the water but feebly and evolves but little heat with it, which, in a word, 

 has little affinity for water. The water in the saturation of sulphuric acid by soda is, so 

 to say, displaced from a stable combination and passes into an unstable combination ; 

 hence an expansion (decrease of sp. gr.) takes place. It is not the reaction of the acid on 

 the alkali, but the reaction of water, that produces the phenomenon by which Ostwald 

 desires to measure the degree of salt formation. The water, which escaped attention, 

 itself has affinity, and influences those phenomena which are being investigated. Further- 

 more, in the given instance its influence is very great because its mass is large. When it 

 is not present, or only present in small quantities, the affinity of the base to the acid leads 

 to contraction, and not expansion. Na.,,O has asp. gr. 2'8, hence its volume = 22; the 

 :!. of SO 5 is 1".) and volume 41, hence the sum of their volumes is 63, and for 

 N : I. .so, the -p. gr. is '2-C,r, and volume 53'6, consequently a contraction of 10 c.c. per gram 

 molecule of salt. The volume of HoSO 4 = 53'3, that of 2XaHO = 37'4; there is produced 

 2H.X), volume = 36 + Xa, SO,, volume f,:l r,. There react 90'7 c.c., and on saturation there 

 results 89*6 c.c. ; consequently contraction again ensues, although less, and although this 

 reaction is one of substitution and not of combination. Consequently the phenomena 

 studied by Ostwald hardly depend on the measure of the reaction of the salts, but more 

 on the relation of the substances dissolved to water. In substitutions, for instance, 

 JNaXO 5 + HoSO, = 2HNO r> + Na,,SO 4 , the volumes vary but slightly; in the above example 

 they are 2(38-8) + 53'3 and 2(41'2) + 53'6 ; hence 131 volumes act, and 136 volumes are pro- 

 duced. It may be thought, therefore, on the basis of what has been said, that on taking 

 water into consideration the phenomena studied by Thomseii and Ostwald prove to be 

 much more complex than they at first appear, and that this method can scarcely lead to 

 a right judgment as to the distribution of acids between 1. 



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