CH. xxvii. HYDROGEN. 229 



acid air. He then weighed it and proved that it was bulk 

 for bulk heavier than common air, and by passing it through 

 water he showed that a quantity of it would dissolve. 



Thus these two men, Black and Bergmann, had arrived 

 at a pretty good knowledge of this gas. They had proved 

 that it is an invisible heavy kind of air ; that it dissolves in 

 water ; that it is acid and joins itself to lime, forming lime- 

 stone or chalk; that it destroys life when breathed, and 

 puts out a flame ; that it is given out by fermenting liquids, 

 and from mineral springs, and is contained in our breath. 

 One thing they had not found out, namely, that it is made 

 up of two elements ; this was discovered by Lavoisier in 

 1779 (see p. 237), when he gave it the name of 'carbonic 

 acid.' 



Discovery of Hydrogen by Cavendish, 1760. The 

 next gas discovered was hydrogen, and its discoverer was 

 Henry Cavendish, grandson of the Duke of Devonshire, who 

 was born in 1731. Cavendish was a very shy and reserved 

 man, who lived much alone, and found his greatest pleasure 

 in studying science for its own sake. It is even related of 

 him that he taught all his servants to understand by signs 

 what he wanted in order that he might be able to think 

 without interruption. 



In the year 1766 he read a paper before the Royal 

 society upon # gas which he called ' inflammable air,' 

 because it burst into a flame- whenever a light was brought 

 near it, and also because he believed it to be the cause of 

 the explosions which so often take place in mines. He 

 obtained this gas by pouring sulphuric acid and water upon 

 zinc, iron, or tin, and then collecting the bubbles as Black 

 had done (see Fig. 40, page 226). But when he began to 

 make experiments with this gas he found it very different 

 from Black's ' fixed air.' It is true that a candle would not 



