120 HISTORY OF CHEMISTRY. [LECTURE VII. 



again, no longer looked upon these substances as salts, but 

 compared them with the oxides. In this connection, the double 

 chlorides and iodides prepared in 1826 by Boullay, caused the 

 latter to develop his ideas more fully. 38 In accordance with 

 these ideas, the chlorides, iodides, etc., of the alkali metals 

 were bases, from which true salts were only produced by com- 

 bination with the chlorides and iodides of the heavy metals ; 

 and the latter, in turn, were analogous with the acids. Others 

 still, and amongst them Berzelius, 34 whose opinion at that time 

 carried the greatest weight, regarded common salt and similar 

 substances as compounds possessing a salt-like character ; but 

 they separated them from ordinary salts. According to them, 

 the whole group of salts consisted of two divisions the amphid 

 salts, to which the oxygen, sulphur, etc., salts belonged, and the 

 haloid salts, which embraced the chlorides, iodides, etc. The 

 latter were composed of two elements or radicals of a metal 

 and a halogen, as chlorine, iodine, cyanogen, etc., at this time 

 came to be called. It remained, however, altogether un 

 explained why substances with such similar properties as those 

 of the amphid salts and the haloid salts, possessed such different 

 constitutions. 



If it was desired to regard the oxygen salts as compounds 

 of an acid with a base, then the establishment of these ideas 

 was further attained as follows. Taking nitre as an example, 

 KO would represent the base, and N 2 O 5 35 the acid (or what 

 we now call the anhydride). It thus came about that acetic 

 acid was represented by C 4 H 6 O 3 , formic acid by C 2 H 2 O 3 , sul- 

 phuric acid by SO 3 , etc. ; that is, instead of the actually exist- 

 ing substances, others were represented, of which some were 

 imaginary. The free acids were held to contain "a proportion 

 of water which we cannot separate except by combining the 

 acid with another substance " ; 3G and although Berzelius him- 

 self had previously distinguished water of hydration from water 

 contained in salts and not necessary for their existence, 37 yet 



33 Ann. Chim. [2] 34, 337 ; Journ. de Pharm. 12, 638. 34 Berzelius, 

 Lehrbuch. Third Edition, 4, 6. :?5 Berzelius' atomic weights : see p. 100. 

 a6 Berzelius, Lehrbuch. Third Edition, 2, 4. 3r Journ. de Phys. 73, 253. 



