XII 



JOSEPH BLACK 



I 728-1 799 



Joseph Black, born in 1^28 at Bordeaux, France, was educated in 

 Belfast and at the University of Glasgow. Before he took his M.D. 

 degree he showed that alkalies were formed, not by their absorbing 

 *^ phlogiston," but by their having carbonic acid gas, or ''fixed air," 

 as a component. In 7755 he was appointed lecturer on che^nistry at 

 Glasgow, and in i/y6 became professor of chemistry at Edinburgh, 

 In i/6j he announced his discovery of latent heat, a principle which 

 has been of great practical value. He died in Edinburgh, Decem- 

 ber 6, 1799. 



THE DISCOVERY OF CARBONIC ACID GAS "^ 



Hoffman, in one of his observations, gives the history of a powder 

 called Magnesia Alba, which has been long used, and esteemed as a 

 mild and tasteless purgative ; but the method of preparing it was not 

 generally known before he made' it public. 



It was originally obtained from a liquor called the Mother of nitre, 

 which is produced in the following manner : 



Salt-petre is separated from the brine which first affords it, or 

 from the water with which it is washed out of nitrous earths, by the 

 process commonly used in crystallizing salts. In this process, the 

 brine is gradually diminished, and at length reduced to a small 

 quantity of an unctuous bitter saline liquor, affording no more salt- 

 petre by evaporation, but, if urged with a brisk fire, drying up into 

 a confused mass, which attracts water strongly, and becomes fluid 

 again when exposed to the open air. 



To this liquor the workmen have given the name of the Mother of 



* From Experiments upon Magnesia, Quicklime, and some other Alkaline 

 Substances (1775). 



