274 
POPULAR SCIENCE REVIEW. 
acted on by sulphurous acid, yet this danger has been entirely 
obviated by the use of manufactured asbestos packing, which is 
now being greatly used for high-pressure steam-engines. 
When required to work in hot climates, the ice-making 
machines most generally in use are open to serious objections* 
and grave inconveniences are experienced in their constant 
employment. Thus ammoniacal machines work at a pressure 
of twenty atmospheres, with water at 80° F., and are thus 
liable to leakage, or even to the danger of an explosion. 
Methylated ether-machines are open to the same objection, in 
addition to which there is a danger of fire when a leakage 
occurs, which unfits them for use at sea. 
Now, in the use of sulphurous acid there is the great advan- 
tage that at 80° F. its tension does not exceed four atmo- 
spheres, while it may be liquefied at 25°, and its tension then is 
only equal to the pressure of the atmosphere. It has no action 
upon metals when kept free from water ; and in order to obtain 
it in a perfectly anhydrous condition, M. Pictet prepares it by 
the action of heat on a mixture of oil of vitriol and sulphur,, 
the gas being dried by oil of vitriol. The condensing and 
refrigerating apparatus consists of tubular vessels similar tO' 
those employed with other liquids, such as ether. 
One of these machines is daily at work at the Chelsea Ice 
Pink, and is capable of making 40 tons of ice per day. The 
skating- floor, which is the invention of Mr. John Gramgee, con- 
sists of a number of flattened metallic tubes placed side by side 
on a bed of concrete or asphalte ; the interior of the tubes is 
kept filled with an uncongealable mixture of glycerine and water, 
which is allowed to flow in from an elevated cistern. Clear ice 
is secured by coating the tubes with water spray, allowing this 
to freeze, and then sprinkling again. During last winter, tubes 
of thin sheet-iron were laid on the floating bath on the Thames, 
at Charing Cross, and a skating-floor was frozen. The tempe- 
rature of an ice-rink from its agreeable coolness has an exhila- 
rating and bracing influence, which dissipates the languor felt in 
a warm moist atmosphere. 
M. Pictet’s machine has interest beyond that of any ordinary 
economical producer of ice, for, constructed as it is with all the 
philosophical thought and scientific knowledge which we usually 
find bestowed only on instruments of research, it has been 
applied by its inventor to the purpose of establishing certain 
simple relations between the latent heat, molecular weights, and 
tensions of the vapours of volatile liquids. 
By the application of mathematical reasoning and the use of 
known data, M. Pictet calculates the latent heat of various- 
liquids, and arrives at the following conclusions : — 
1. Cohesion is a constant quantity for all liquids. 
