306 A SHORT HISTORY OF SCIENCE 



To sum up : It was now known that there exists an invisible, 

 odorless gas, resembling air but heavier than air and more soluble 

 in water ; that it is acid, and capable of attaching itself to lime, 

 making a kind of chalk ; that it will not support life, yet is present 

 in the human breath, as well as in some mineral waters ; and that 

 it is given off during fermentations. It only remained for Lavoisier 

 to discover (in 1779) that this gas is compounded of two very 

 common elements carbon and oxygen tightly bound together, 

 and may therefore be called, as it often is today, "carbonic acid." 

 But before this could happen other investigations had to prepare 

 the way, and especially the discovery of the new "element," 

 oxygen. 



A NEW CHEMISTRY. PRIESTLEY AND LAVOISIER. We have 

 now reached a period of remarkable activity and rapid progress 

 in chemical research. While Black was hard at work upon chemi- 

 cal problems in Scotland, and Bergmann in Sweden, Cavendish 

 was similarly engaged in England, and in 1766 reported to the 

 Royal Society his discovery of a new kind of gas to which, for 

 the reason that it took fire whenever flame was applied to it, 

 and also because he believed it to be the cause of the occasional 

 explosions in mines, he gave the name "inflammable air." 

 Cavendish obtained this gas by treating iron, tin, zinc, or other 

 metals with sulphuric acid, very much as Black had obtained 

 fixed air by treating limestone with acids. Inflammable air 

 was, however, obviously quite unlike fixed air, since it was 

 lighter than air - - not heavier - - and was readily burned. It 

 resembled it, nevertheless, in that a lighted candle plunged into 

 it went out, and animals died in it just as they did in fixed 

 air. It had another peculiar property ; viz. that of forming with 

 air an explosive mixture. This new gas as we now know was 

 hydrogen. 



Not long after, in 1772, other new gases were separated 

 and studied; viz. nitrogen by Rutherford, and nitric oxide by 

 Priestley. It was on August 1, 1774, however, that Priestley 

 made his most important discovery, and one that proved to be the 

 very corner-stone of the splendid edifice in which modern chem- 



