6 BLACK. 



research, as those discoveries, the materials of his in- 

 duction, were the undivided property of others ! 



The capital discovery of Black, thus early made, and 

 to any share in which no one has ever pretended, was 

 that the causticity, as it was formerly termed upon a 

 false theory, of the alkalis and alkaline earths, was owing 

 to the loss of a substance with which they had been 

 combined, and that their reunion with this substance 

 again rendered them mild. But the nature of this sub- 

 stance was likewise ascertained by him, and its detection 

 forms by far the most important part of the discovery, 

 for it laid the foundation of chemical science. 'He 

 found that it was a permanently elastic fluid, like air 

 in some of its mechanical qualities, those of being 

 transparent or invisible, and incondensable, but differ- 

 ing entirely from the air of our atmosphere in its chemi- 

 cal properties. It was separated from alkaline substan- 

 ces by heat, and by the application of acids, which, 

 having a stronger elective affinity for them, caused it 

 to be precipitated, or to escape in the aeriform state ; 

 it was heavier than common air, and it gave a slight 

 acidulous flavour to water on being absorbed by it ; 

 hence the inference that it was an acid itself. A short 

 time afterwards (in 1757) he discovered that this pe- 

 culiar air is the same with that produced by the fer- 

 mentation of vegetable substances. This he ascer- 

 tained by the simple experiment of partially emptying 

 in a brewer's vat, where the fermenting process was 

 going on, the contents of a phial filled with lime-water. 

 On shaking the liquid that remained with the air that 

 had entered, he found it become turbid, from the lime 

 having entered into union with the air, and become 

 chalk. The same day he discovered by an experiment, 

 equally simple and equally decisive, that the air which 

 comes from burning charcoal is of the same kind. He 

 fixed a piece of charcoal in the broad end of a bellows 

 nozzle, unscrewed ; and putting that in the fire, he in- 

 serted the other end in a vessel filled with lime-water. 



