1 8 THE SCIENTIFIC PAPERS OF 



The author pursued these experiments at long intervals since 

 the year 1847, with no other object in view than to extend his 

 own information ; and, consequently, without pretence to 

 generalisation or extreme accuracy. The question, however, is 

 one of great practical importance to engineers, and with the 

 advantage of valuable suggestions and the co-operation of his 

 friends, Mr. Edward A. Cowper and Mr. William P. Marshall, 

 the author has again taken up the experiments, which, having 

 been referred to at the previous meeting by Mr. Cowper, he feels 

 himself called upon to lay before this Institution in their present 

 state, though incomplete. 



The amount of heat required to convert one pound of water 

 into steam of different pressures has occupied the attention of 

 natural philosophers from the earliest periods of the modern 

 steam engine. 



Dr. Black observed, about a century ago, that a large quantity 

 of heat was absorbed by water in its conversion into steam (not 

 accompanied by an increase of temperature), which he termed 

 " the latent heat of steam." His apparatus consisted simply of 

 a metallic vessel containing water, which he exposed to a very 

 regular fire ; and from the comparative time which was occupied, 

 first in raising the temperature of the water to the boiling point, 

 and, secondly, in effecting the evaporation, he approximately 

 determined the amount of latent heat. Resuming the experi- 

 ment, in conjunction with Dr. Irvine, he employed a different 

 apparatus, consisting of a steam generator, and of a surface 

 condenser, or 'a serpentine tube, surrounded by a large body of 

 cold water. 



The steam which condensed in the serpentine tube was care- 

 fully collected and weighed, and the rise of temperature of the 

 surrounding water was observed, which, multiplied by its known 

 quantity, represented the total quantity of heat which the steam 

 had yielded. 



The quantity of heat requisite to raise the temperature of one 

 pound of water through 1 Fahr. being taken for the unit of heat, 

 Black and Irvine obtained for the total quantity of heat in 



Steam of atmospheric pressure, the number . . 954 

 Southern . 1021 



