486 Additional Notes. 



theless, his opinion, like every other which he advanced in 

 chemistry, continued to have supporters for a long time, and 

 ■was even mentioned by Macquer. At last its defects be- 

 gan to be perceived. Bergman and Scheele declared openly 

 against It; and their discoveries, together with those of La- 

 voisier, demonstrated the falsehood of both parts of the 

 theory, by showing that sulphuric acid does not exist in the 

 other acids, and that it is not composed of water and earth, 

 but of sulphur and oxygen. 



** The opinion, however, that acidity Is owing to some 

 principle common to all the salts, was not abandoned. Wal- 

 lerius, Meyer and Sage had advanced different theories 

 in succession about the nature of this principle; but as they 

 were formed rather on conjecture and analogy than direct 

 proof, they obtained but a few advocates. At last M. La- 

 voisier, In 1778, by a number of ingenious and accurate 

 experiments, proved that several combustible substances, when 

 united with oxygen, form acids; that a great number of 

 acids contain oxygen ; and that, when this principle Is sepa- 

 rated from them, they lose their acid properties. He con- 

 cluded, therefore, that oxygen is the acidifying 'principle, as 

 the word Imports, and that acids are nothing else but com- 

 bustible substances combined with oxygen, and differing 

 from one another according to the nature oi the combustible 

 base." — See Thompson's Chemistry, 



This doctrine, with few exceptions, has been confirmed 

 by subsequent experiments, and Is now generally received 

 among chemists. 



Nexv Acids, p. 83. 



The Acids known at the close of the eighteenth century 

 amount to about thirty, the greater part of which have been 

 discovered within the last forty years. Of these nearly one 

 third were discovered by the celebrated Scheele, and the 

 remainder chiefly by Margraaf, Priestley, Lavoisier, 

 Vauuuelin, Berthollet, and Kter. 



Composition of the Atmosphere, p. 83. > 



For our knowledge of the component parts of atmospheric 

 air, we are indebted to the successive experiments and disco-* 



