DISCOVERY BY EXAMINING THE EFFECTS OF HEAT. 553 



Professor Bergmann. He did so accordingly, but Berg- 

 mann was as unable to find an explanation as himself. 

 On returning a few days after to Mr. Loock's shop, Gahn 

 was informed that there was a young man in the shop who 

 had given an explanation of the phenomenon. This young 

 man was Scheele, who had informed Mr. Loock that there 

 were two species of acids confounded under the name of 

 spirit of nitre, what we at present call nitric and hypo- 

 nitrous acids. Mtric acid has a stronger affinity for 

 potash than vinegar has, but hyponitrous acid has a 

 weaker. The heat of the fire changes the nitric acid of 

 the saltpetre to hyponitrous, hence the phenomenon.' l 

 It was by observing that when ' mercurial calx ' (i.e. oxide 

 of mercury) was heated alone, it evolved ' pure air ' (i.e. 

 oxygen), and when heated with charcoal it gave out ' fixed 

 air' (i.e. carbonic anhydride) that Lavoisier in 1775 dis- 

 covered that ' fixed air ' is composed of ' pure air ' united 

 to carbon. It was also by the application of heat to the 

 junction of two metals, viz., bismuth and copper, connected 

 with a galvanometer, that Seebeck in 1822 made the 

 important discovery of thermo-electricity ; and by ex- 

 posing prismatic crystals of sulphate of nickel to solar 

 heat, Mitscherlich discovered that they became altered in 

 structure and converted into minute octohedrons with 

 square bases. 



Many discoveries have been made by applying elec- 

 tricity to bodies and examining the effects. In this way 

 Otto Gkiericke discovered that electrified bodies repel each 

 other. By imparting static electricity to an insulated 

 wire, 666 feet long, Gray and Wheler, in the year 1729, 

 discovered the important fact of electric conduction. By 

 the same method, between the years 1720 and 1736, the 



1 Thomson, Histoi*y of Chemisti*y, vol. ii. p. 56. 



