OXYGEN AND THE NATURE OF ACIDS. 127 



GENERAL CONSIDERATIONS ON THE NATURE OF ACIDS * 



By ANTOINE-LAURENT LAVOISIER. 



WHEN" the chemists of olden times had reduced a body to oil, salt, 

 earth and water, they believed that they had reached the limits 

 of chemical analysis, and consequently they gave to salt and to oil the 

 names of 'principles of bodies.' 



In proportion as the art made progress, the chemists who succeeded 

 them became aware that substances which had been held to be primary 

 could be decomposed, and they recognized in succession that all the 

 neutral salts, for instance, were formed by the union of two substances, 

 an acid of some sort and a salt, earth or metal. 



Hence arose the entire theory of neutral salts which has held the at- 

 tention of chemists for over a century, and which is to-day so near per- 

 fection that we may regard it as the surest and most complete part of 

 chemistry. 



Chemical science has been handed down to us in this condition, and 

 it is our business to do with the constituents of the neutral salts what 

 the chemists who went before us did with the neutral salts themselves, 

 to attack the acids and bases and to carry chemical analysis along this 

 line a step beyond its present limits. 



I have already imparted to the Academy my first efforts in this field. 

 I have in earlier memoirs demonstrated to you as far as it is possible 

 to demonstrate in physics and chemistry that the purest air, that to 

 which M. Priestley has given the name of 'dephlogisticated air,' enters 

 as a constituent part into the composition of several acids, notably of 

 phosphoric, vitriolic and nitric acids. 



More numerous experiments put me in a position to-day to draw gen- 

 eral conclusions from these results and to assert that the purest air, the 

 air most suitable for respiration, is the principle which causes acidity; 

 that this principle is common to all acids, and that in addition one or 

 more other principles enter into the composition of each acid, differenti- 

 ating it and making it one sort of acid rather than another. 



In consequence of these facts, which I already regard as very firmly 

 established, I shall henceforth call dephlogisticated air or air most suit- 

 able for respiration, when it is in a state of combination or fixity, by the 

 name of 'the acidifying principle,' or, if one prefers the same meaning 

 in a word from the Greek, 'the principle Oxyginej 1 This nomenclature 

 will save periphrases, will make my statements more exact, and will 

 avoid the ambiguities I would be likely to fall into constantly if I used 

 the word 'air.' 



* Read before the Paris Academy of Sciences on September 5,1777. Translated for The Popu- 

 lar Science Monthly from the ' Comptes Rendus ' for the meeting. 



