330 Biographical Account of [Nov. 



theory explain all the cases which are conformable to his law, 

 and those likewise which do not agree with it ; and we can 

 explain the composition of the muriates just as easily on the 

 hypothesis that chlorine is simple as that it is compound. 

 Chlorine, indeed, for any thing we know to the contrary, may 

 be a compound, and may contain oxygen as one of its consti- 

 tuents ; so may azote, and so may iron. But our opinions 

 respecting the composition of bodies must be conformable to the 

 evidence which is laid before us ; otherwise we forsake the 

 road of science, and get into that of fancy and romance. 



The rules for investigating chemical phenomena are sufficiently 

 simple, and may be reduced to the following. 



(1.) Eveiy fact must be established by satisfactory experi- 

 ments. 



(2.) A body must be considered as simple unless satisfactory 

 evidence can be brought to show that it is a compound. 



(3.) The most satisfactory way of showing a body to be a 

 compound is to separate its constituents, exhibit them in a 

 separate state, and to show that by uniting them again together, 

 the original compound body is produced. 



(4.) When a substance cannot be exhibited in a separate state, 

 it is always hazardous to draw any peremptory conclusions 

 respecting its existence. Our conclusions should be given only 

 as hypothetical or conjectural ; because the only unequivocal 

 evidence of the existence of a chemical body is wanting. The 

 existence of the principle called phlogiston, so universally 

 admitted at one period, is an example in point, which should 

 make us cautious in our conclusions. 



2. On Carbonic Acid. — Bergman seems to have been the 

 first who considered this substance as an acid. His opinions 

 on the subject were communicated to foreign chemists in 1770, 

 and his first essay on this acid made its appearance in 1773. 

 It would be needless, considering the present state of our 

 knowledge, to give a minute account of this essay, though at 

 the time of its publication it must have been exceedingly valuable. 

 He describes the mode of procuring this gas, shows that it 

 possesses the properties of an acid ; that water at the tempera- 

 ture of 41° absorbs rather more than its bulk of it; that the 

 specific gravity of such water is T0015 ; that the specific 

 gravity of carbonic acid gas is rather more than 1*5, and that it 

 combines with the different bases, and forms salts. He prepared 

 and described bicarbonates of potash and soda, carbonate of 

 ammonia, carbonate of barytes, carbonates of magnesia, zinc, 

 and manganese. He determined the order of the affinities of 

 carbonic acid for the bases ; and he showed that it is the 

 weakest of all the acids known when he wrote. 



3. Of the Analysis of Waters. — This paper, first published in 

 1778, was of great importance at the time of its appearance. In 

 it the method of analyzing waters is first laid down. Before the 



