SODIUM CHLORIDE-BERTHOLLET'S LAWS 44$ 



which can be compared with these reactions for simplicity are those 

 exchange decompositions investigated by G. G. Gustavson, which 



method will be clearly understood from an example. A solution of caustic soda containing 

 an almost molecular (40 grams) weight per litre had a specific gravity of 1*04051. The 

 specific gravities of solutions of equal volume and equivalent composition of sulphuric 

 and nitric acids were T02970 and 1'03084 respectively. On mixing the solutions of 

 NaHO and H 2 S0 4 there was formed a solution of Na 2 S0 4 of sp. gr. 1-02959; hence 

 there ensued a decrease of specific gravity which we will term Q, equal to 1-04051 

 4-r02970-2(r02959) = 0-01103. So also the specific gravity after mixture of the solutions 

 of NaHO and HNO 3 was 1-02633, and therefore Q = 0-01869. When one volume of the 

 solution of nitric acid was added to two volumes of the solution of sodium sulphate, a 

 solution of sp. gr. 1-02781 was obtained, and therefore the resultant decrease of sp. gr. 



Q x = 2(1-02959) + 1-03084 - 8(1 : 02781) = 0'00659. 



Had there been no chemical reaction between the salts, then according to Ostwald's 

 reasoning the specific gravity of the solutions would not have changed, and if the nitric 

 acid had entirely displaced the sulphuric acid Q 2 would be = 0-01869- 0-01103 = 0'00766. 

 It is evident that a portion of the sulphuric acid was displaced by the nitric acid. But the 

 measure of displacement is not equal to the ratio between Q t and Q 2 , because a decrease 

 of sp. gr. also occurs on mixing the solution of sodium sulphate with sulphuric acid, 

 whilst the mixing of the solutions of sodium nitrate and nitric acid only produces a slight 

 variation of sp. gr. which falls within the limits of experimental error. Ostwald deduces 

 from similar data the same conclusions as Thomsen, and thus reconfirms the formula 

 deduced by Guldberg and Waage, and the teaching of Berthollet. 



, The participation of water is seen still more clearly in the methods adopted by 

 Ostwald than in those of Thomsen, because in the saturation of solutions of acids by 

 alkalis (which Kremers, Reinhold, and others had previously studied) there is observed, 

 not a contraction, as might have been expected from the quantity of heat which is then 

 evolved, but an expansion, of volume (a decrease of specific gravity, if we calculate as 

 Ostwald did in his first investigations). Thus by mixing 1,880 grams of a solution of 

 sulphuric acid of the composition SO 3 + 100H 2 0, occupying a volume of 1,815 c.c., with a 

 corresponding quantity of a solution 2(NaHO + 5H 2 O), whose volume =1,793 c.c., we 

 obtain not 8,608 but 3,633 c.c., an expansion of 25 c.c. per gram molecule of the resulting 

 salt, Na 2 SO4. It is the same in other cases. Nitric and hydrochloric acids give a still 

 greater expansion than sulphuric acid, and potassium hydroxide than sodium hydroxide, 

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

 sidered as 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 sepa- 

 rated from such solutions with great difficulty. After mutual saturation they form the 

 salt Na 2 SO 4 , which retains the water but feebly and evolves but little heat with it, i.e., in 

 other words, has little affinity for water. In the saturation of sulphuric acid by soda the 

 water is; so to say, displaced from a stable combination and passes into an unstable com- 

 bination ; 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. 

 Furthermore, 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 attraction of the base to the 

 acid leads to contraction, and not expansion. Na 2 O has a sp. gr. 2-8, hence its molecular 

 volume = 22 ; the sp. gr. of SOj is 1*9 and volume 41, hence the sum of their volumes is 63 ; 

 for Na, 2 SO 4 the sp. gr. is 2'65 and volume 53'6, consequently there is a contraction of 10 c.c. 

 per gram-molecule of salt. The volume of H 2 SO 4 = 53'3, that of 2NaHO = 37'4 ; there is 

 produced 2H 2 O, volume = 36, + NagSO^ volume = 53'6. There react 90'7 c.c., and on satu- 

 ration there result 89'6 c.c. ; consequently contraction again ensues, although less, and 



