ON ICE-MAKING AND ICE- MACHINES. 
271 
quantity of heated air or water down to a moderate tempera- 
ture, a large supply of water is the best medium, not only on 
account of its abundance and cheapness, hut because of its great 
capacity for heat. 
When any elastic fluid is compressed, it becomes hot, and if 
it then be cooled down to its original temperature and be ex- 
panded, it is rendered as many degrees colder by its rarefaction 
as it was heated by its condensation; hence we have here a 
means of producing low temperatures. On the one hand we can 
ignite tinder by the heat evolved in the compression of air in a 
glass cylinder ; and by the exhaustion of air in a bell jar the 
temperature may be reduced so that the moisture it contains is 
deposited as a mist. By the extremely rapid expansion of a 
liquefied gas when pressure is removed, or of a volatile liquid 
when its evaporation is hastened by mechanical means, we ob- 
tain the most effective cooling powers. The familiar experiment 
of freezing water or mercury in a red-hot dish is effected by the 
enormous expansion of liquefied sulphurous acid or of solidified 
carbonic acid, which substances regain the heat they lost when 
undergoing the change of liquefaction or solidification. 
The production of intense cold by the rapid evaporation of 
ether projected in the form of a fine spray is a process which has 
been introduced with success into surgery by Dr. Bichardson, 
for the purpose of producing a local insensibility to the pain 
caused by a knife or other instrument. 
By enclosing ether in an air-tight vessel, and drawing off the 
vapour as fast as it is generated, evaporation is greatly ac- 
celerated, while the ether may be condensed again for further 
use. The original apparatus of Harrison, which depended upon 
this principle, consisted of a multitubular boiler immersed in an 
uncongealable liquid such as brine ; an exhaust pump carried off 
the ether vapour which is rapidly formed at the expense of the 
warmth of the salt water. The reduction of temperature may 
reach 24° F., or what is commonly called 8° of frost. The ether 
was condensed by passing through a worm tube surrounded by 
a stream of cold water, and the chilled brine was made to cir- 
culate round metallic vessels containing the water to be con- 
verted into ice. 
Many improvements have been made on this ether machine, 
and one of the most complete methods of working is now in 
operation on a large scale on the premises of the Manchester 
Patent Ice Company. 
Messrs. Sidely and Mackay, of Liverpool, are the patentees 
of the apparatus, the chief characteristics of which are its adapt- 
ability to the satisfying of large demands, its economical use 
of the cooling power of the ether vapour, and its capability of 
making ice in thick blocks. Hot only are exhaust pumps used 
