THE EARLY DAYS OF CHEMISTRY 15 



argentaurum, by hammering silver, and to have trans- 

 muted it, by a further process, into gold. He claims, 

 too, that Sir William Crookes has obtained proof, slight 

 it is true, though decisive, of an increase in the quantity 

 of gold in a Mexican dollar, after treating the latter by 

 his process. 



We have seen from what precedes that the doctrine 

 concerning elements, held from remote times, was that 

 they were four in number, earth, water, air, and fire. 

 That besides these, there exist three chemical or ' hypo- 

 static ' principles, to wit, sulphur, mercury, and salt. In 

 spite of the refutation of such views by the Honourable 

 Robert Boyle, which we shall consider later, they lingered 

 on until the middle of last century, being quoted in 

 almost all treatises on chemistry. Macquer's Chemistry, 

 a text-book which obtained a wide circulation in its day, 

 gives the following description of the ancient elements 

 (1768): 'Air is the fluid which we constantly breathe, 

 and which surrounds the whole surface of the terrestrial 

 globe. Being heavy, like all other bodies, it penetrates 

 into all places that are not either absolutely inaccessible 

 or filled with some other body heavier than itself. Its 

 principal property is to be susceptible of condensation 

 and rarefaction; so that the very same quantity of Air 

 may occupy a much greater or a much smaller space, 

 according to the different state it is in. Heat and cold, or, 

 if you will, the presence or absence of the particles of Fire, 

 are the most usual causes, and indeed, the measure of its 

 condensation and rarefaction : for, if a certain quantity of 

 air be heated, its bulk increases proportionately to the 

 degree of heat applied to it ; the consequence of which is, 

 that the same space now contains fewer particles than 

 it did before.' ' Air enters into the composition of many 

 substances, especially vegetable and animal bodies ; fully 

 analysing most of them, such a considerable quantity 



