JOSEPH BLACK: HIS LIFE AND WORK 85 



which is customary nowadays, and it is still uncertain to 

 one seven-hundredth of its value. Black's determination 

 was a remarkably good one, especially if we consider the 

 crude appliances which he used. 



The substance of this research was communicated to 

 the ' Philosophical Club/ or Society of Professors and 

 others in the University of Glasgow in the year 1762, and 

 was expounded yearly by Black in his lectures to his 

 students. 



Black suggested to Irvin, his pupil, and afterwards his 

 successor in the Glasgow chair, to determine the latent 

 heat of fusion of spermaceti and bees'-wax ; and he found 

 that these substances, too, absorb heat, insensible to the 

 thermometer, on assuming the liquid state. In this 

 manner, he made his thesis general. But in attempting 

 to extend it beyond the case of liquids and solids, he went 

 astray. For example, he imagined that the great rise of 

 temperature, which may even reach redness, caused by the 

 hammering of iron by a skilled smith, was due to the 

 ' extrication of the latent heat of the iron by hammering/ 

 He did not realise that heat can be produced from 

 mechanical work; that work can be quantitatively trans- 

 formed into heat; a discovery made more than eighty 

 years later, by Joule, although it had been anticipated by 

 Count Rumford, and by Sir Humphry Davy, in the begin- 

 ning of last century. 



Similar experiments were made by Black on the latent 

 heat of steam, in which he compared the time required for 

 a known weight of water to rise through a definite interval 

 of temperature when exposed to a constant supply of heat 

 with that required to dissipate the water into steam, But 

 his estimate of 830 units required to evaporate one part of 

 water was not so accurate ; the actual figure is 967 units on 

 the Fahrenheit scale. Black cited experiments by Boyle, 

 by Robison, his successor in the Glasgow chair, and by 



