COMPOUNDS OF CARBON WITH OXYGEN AND NITROGEN 389 



acid may, however, be judged from the joint evidence of many properties. 

 With such energetic alkalis as soda and potash, carbonic acid forms 

 normal salts, soluble in water, but having an alkaline reaction and in 



composed with difficulty by heat and water, whilst others, like carbonic and hypochloroua 

 acids, do not combine with feeble bases, and with most of the other bases form salts which 

 are easily decomposed. The same may be said with regard to bases, among which those of 

 potassium, K 2 O, sodium, Na. 2 0, and barium, BaO, may serve as examples of the most 

 powerful, because they combine with the most feeble acids and form a mass of salts of 

 great stability, whilst as examples of the feeblest bases alumina, ALO 3 , or bismuth oxide, 

 Bi^Os, may be taken, because they form salts easily decomposed by water and by heat 

 if the acid be volatile. Such a division of acids and bases into the feeblest and most 

 powerful is justified by all evidence concerning them, and is quoted in this work. But 

 the teaching of this subject in certain circles has acquired .quite a new tone, which, in my 

 opinion, cannot be accepted without certain reservations and criticisms, although it com- 

 prises many interesting features. The fact is that Thomsen, Ostwald, and others proposed 

 to express the measure of affinity of acids to bases by figures drawn from data of the 

 measure of displacement of acids in aqueous solutions, judging (1) from the amount of 

 heat developed by mixing a solution of the salt with a solution of another acid (the 

 avidity of acids, according to Thomsen); (2) from the change of the volumes accom- 

 panying such a mutual action of solutions (Ostwald) ; (3) from the change of the 

 index of refraction of solutions (Ostwald), &c. Besides this there are many other 

 methods which allow us to form an opinion about the" distribution of bases among 

 various acids in aqueous solutions. Some of these methods will be described 

 hereafter. It ought, however, to be remarked that in making investigations in aqueous 

 solutions the affinity to water is generally left out of sight. If a base N, combining 

 with acids X and Y in presence of them both, divides in such a way that one- 

 third of it combines with X and two-thirds with Y, a conclusion is formed that the affinity, 

 or power of forming salts, of the acid Y is twice as great as that of X. But the presence 

 of the water is not taken into account. If the acid.X has an affinity for water and for N 

 it will be distributed between them ; and if X has a greater affinity for water than Y, 

 then less of X will combine with N than of Y. If, in addition to this, the acid X is 

 capable of forming an acid salt NX 2 , and Y is npt, the conclusion of the relative strength 

 of X and Y will be still more erroneous, because the X set free will form such a salt on 

 the v addition of Y to NX. We shall see in Chapter X. .that when sulphuric and nitric 

 acids in weak aqueous solution act on sodium, they are distributed exactly in this way : 

 namely, one-third of the sodium combines with the sulphuric and two-thirds with the 

 nitric acid ; but, in my opinion, this does not show that sulphuric acid, compared with 

 nitric acid, possesses but half the degree of affinity for bases like soda, and only demon- 

 strates the greater affinity of sulphuric acid for water compared with that of nitric acid. 

 In this way the methods' of studying the distribution in aqueous solutions probably only 

 shows the difference of the relation of the acid to a base .and to water. 



In view of these considerations, although the teaching of the distribution of salt- 

 forming elements in aqueous solutions is an object of great and independent interest, it 

 can hardly serve to determine the measure of affinity between bases and acids. Similar 

 considerations ought to bo kpt in view when determining the energy of acids by means of 

 the electrical conductivity of their weak solutions. This method, proposed by Arrhenius 

 (1884), and applied on an extensive scale by Ostwald (who developed it in great detail in 

 his Lehrbucli d. allgemeinen Chemie, v. ii., 1887), is founded on the fact that' the re-; 

 lation of the so-called molecular electrical-conductivity of weak solutions of variou? acids 



(I) coincides with the relation in which the same acids stand according to the distribution, 



(II) found by one of the above-mentioned methods, and with the relation deduced for 

 them from observations upon the velocity of reaction, (III) for instance, according to the 

 rate of the splitting up of an ethereal salt (into alcohol and acid), or from the rate of the so- 

 called inversion of sugar that is, its transformation into glucose as is seen by comparing 



