68 Britain's Heritage of Science 



deprived of its air could be undercooled as well as ordinary 

 water, concluded that the cause of the difference lay in the 

 act of re-absorbing the air. He suggested that the absorp- 

 tion caused (possibly through minute differences of tempera- 

 ture or density) sufficient circulation, or, as he expressed it, 

 " agitation " to prevent the undercooling. It is remarkable 

 that the subject has never been examined further, but 

 Black's explanation finds some support in the experiments 

 made by Thomas Graham, who showed that the admission 

 of air into a previously boiled and undercooled solution of 

 Glauber salt, set the crystallization going, and this was 

 traced to a slight diminution of the solubility of the salt 

 in water which contains air. 



To Black must also be given a place in the history of 

 aeronautics, as he was the first to make the attempt to fill 

 a balloon with hydrogen; this was as early as 1767, two 

 years before Montgolfier made his first balloon ascent. 



Black practised as a medical man ; he held for a time the 

 Chair of Anatomy and Chemistry at Glasgow, but distrustful 

 of his qualifications as a chemist, exchanged it for that of 

 Medicine. In 1766 he succeeded Cullen in the Professorship 

 of Medicine and Chemistry at Edinburgh. In private life 

 he was fond of painting; the weakness of his health is 

 probably responsible for a certain lack of energy which 

 sometimes led him to abandon his work when half finished, 

 and to leave many of his researches unpublished. " No man 

 had less nonsense in his head," said Adam Smith, " than 

 Black." 



One further contribution of the Scotch Universities to 

 chemistry remains to be noticed. Rutherford (1749-1819), 

 a medical man who occupied the Chair of Botany at Edin- 

 burgh, was the first to isolate the gas nitrogen in 1772, by 

 burning substances in an enclosed volume of air, and 

 absorbing the carbonic acid formed in the combustion. 



Black's lectures were edited after his death by John 

 Hobison (1739-1805), a man of great intellectual powers, 

 who, like so many other men of science of the time, led an 

 eventful life. After a brief period of study at Glasgow, he 

 became tutor to the son of Admiral Knowles, who as a 

 midshipman was about to accompany General Wolfe to 



