A CENTURY OF CHEMISTRY. 71 



carbon; and (2) others which, by heating or other- 

 wise, can be broken up (not sorted out) into unlike 

 parts, such as sugar and salt. In other words, after 

 sorting out the heterogeneous mixtures the chemist 

 has to do with the two sets of homogeneous stuffs to 

 which we have just referred which are familiarly 

 known as Elements and Compounds. 



Though many of the elementary substances, such 

 as copper, gold, iron, lead, silver, tin, zinc, sulphur, 

 have been known from remote antiquity, the recogni- 

 tion of elements as such i.e., as substances which 

 cannot, so far as we know at the time, be resolved 

 into other kinds of matter practically dates from 

 Robert Boyle, the author of The Sceptical Chymist 

 (1680). 



A hundred years later, Lavoisier, who first made 

 the conception of elements practically useful in 

 scientific research, enumerated thirty-three (includ- 

 ing light and heat), but the list increased by leaps 

 and bounds during the nineteenth century. Thus Sir 

 Humphry Davy discovered six new metals between 

 1808 and 1810, and the Swedish chemist Berzelius 

 added an equal number in about the same time. As 

 was to be expected, the practical interests of miner- 

 alogy and metallurgy, especially in Sweden and 

 Germany, gave zest to the search after elements, 

 and led Scheele and others to many discoveries. 

 By 1830, Lavoisier's list was nearly doubled, and it 

 is still being added to. 



Interactions of Elements. Another impression 

 that we get from our outlook is that things are 

 changeful. We see stones weathering and crum- 

 bling, shells being dissolved away, iron rusting, coal 

 burning, and thousands of other changes, which ex- 

 cite curiosity and offer problems to be solved. 



