226 ANNUAL OF SCIENTIFIC DISCOVERY. 



ter. The existence of anhydrous sulphuric acid in an isolated state, 

 and the fact that it so readily combines with water, was urged as an 

 argument in favor of this theory ; and the same holds good with phos- 

 phoric, carbonic, sulphurous, lactic, nitrous, and even (according to 

 the recent discovery of Dessaignes) nitric acid. However simple this 

 view might appear, and however satisfactory it might be in explaining 

 those cases of combination for which it was specially intended, chem- 

 ists soon became acquainted with bodies perfectly analogous in their 

 general properties to the oxygen-acids, and producing by their action 

 upon bases similar effects, but which, from the fact of their containing 

 no oxygen, could not possibly be conceived as made up of water and 

 an anhydrous acid. For instance, hydrochloric acid was proved, both 

 analytically and synthetically, to be composed of nothing but chlorine 

 and hydrogen ; and when it combines with potash, the hydrogen is 

 found to leave the chlorine, whilst potassium takes its place. Being 

 desirous of simplifying as far as possible their views of these phenome- 

 na, and of extending the same explanation to all like cases, certain 

 chemists were led to imagine a new mode of representing the constitu- 

 tion and reactions of oxygen acids, which had the advantage of con- 

 necting the two classes of analogous reactions by the same theory. 

 This consisted in conceiving, that in the formation of a hydrated acid 

 a compound radical is produced in combination with hydrogen ; so 

 that hydrated sulphuric acid is the hydrogen-compound of S O 4 , in the 

 same way as hydrochloric acid is the hydrogen-compound of chlorine. 

 There were many arguments in favor of this view, amongst which the 

 most prominent was derived from the fact, that when a salt of the one 

 class, as chloride of potassium, decomposes a salt of the other, as sul- 

 phate of silver, the result is exactly in conformity with what must oc- 

 cur on the supposition of the compound radical ; and in like manner, 

 the electrolytic decomposition of a sulphate moves the group S O 4 to 

 the positive pole, where it either combines with a metal or undergoes 

 decomposition. One of the strongest arguments against the view that 

 the oxygen acids contain water, is afforded by the results of recent re- 

 searches (especially of MM. Laurent and Gerhardt) on the atomic 

 weight of acids. Those chemists have rendered more definite and ex- 

 act than they had been before, our ideas on the distinctions between 

 monobasic, bibasic, and tribasic acids, and have clearly established that 

 the correct expression of the atom of nitric acid must be such as con- 

 tains half as much hydrogen as is contained in one atom of water (in- 

 asmuch as water is bibasic, and nitric acid monobasic). Of course, 

 this proportion may be as well established by doubling the atomic 

 weight of water as by halving that of hydrated nitric acid ; but either 

 way it is clear that hydrated nitric acid cannot contain water. Such 

 was the position of the question, when an English chemist proved that 

 the formation of ether from alchohol (which was considered chemically 

 as the hydrate of ether,) does not consist in a separation of two already 

 formed compounds, but in a substitution of hydrogen by the organic 

 radical ethyl. A similar fact M. Gerhardt has proved respecting a 

 gr$at number of organic acids, by preparing bodies which stand to 



