MODERN SCIENCE. 177 



to salts (i.e., the compounds of acids with their bases). He 

 divided matter into THREE FORMS (solid, liquid, gaseous) 

 according to the degree of heat ; established the principle of 

 the "conservation of mass that in no process of change is 

 there any alteration in the total mass of matter taking part in 

 that change " ; discovered phosphoric acid, and described 

 some of the substances formed by combining it with various 

 bases; foresaw the existence of the metals potassium and 

 sodium ; discovered also the exact composition of water ; 

 established the distinction between COMPOUNDS and 

 ELEMENTS, and laid down the definition of the latter; 

 established the law of fixity of composition of chemical com- 

 pounds; determined the properties of oxygen, calling it 

 " acid-producer," believing it to enter into the composition of 

 all acids a generalisation which admits of exceptions (see 

 Davy). By his immense work Lavoisier gave a new impulse 

 to the advance of chemistry, so long arrested by Stahl's 

 hypothesis. He showed that there is no such thing in nature 

 as " transmutation " in the alchemical sense of the word. He 

 applied CHEMISTRY to PHYSIOLOGY, and explained the two 

 hypotheses of respiration one of which, that respiration is 

 a process chemically similar to that of calcination, modern 

 science has confirmed. 



We may point out that the successive discovery of the 

 four gases carbonic acid, hydrogen, nitrogen (found by 

 Rutherford in 1772), and oxygen revolutionised chemistry 

 in a manner the importance of which cannot be exaggerated. 

 These four gases play the main part in the maintenance of 

 vegetable and animal life. " Out of the raw material," says 

 Dr. Crum-Brown, " gathered by Black, Scheele, Priestley, and 

 Cavendish, Lavoisier constructed a consistent and compre- 

 hensive theory upon which the subsequent progress is firmly 

 grounded." Chemistry with him and his school became 

 once more a quantitative science (that is, components of a 

 substance were now carefully weighed) instead of being 

 merely qualitative. Another remark to be made is that 

 Lavoisier's nomenclature aids science by its simplicity and 

 clearness instead of fixed air we have carbonic acid, which 

 is thoroughly descriptive of the nature of this gas ; instead 



N 



