The matter of fire is _elastic_, as is proved evidently from all its effects. There is indeed reason to believe, that caloric is the only fluid in nature which is permanently elastic, and that it is the cause of the elasticity of all fluids which are esteemed so. From the elasticity of this element it results, that all natural bodies can only retain a certain quantity of it, without undergoing an alteration in their state and form. Thus a moderate quantity of fire admitted into a solid body expands it; a still larger quantity renders it fluid; and if the quantity is still increased, it will be converted into vapor. Caloric expands all bodies which it penetrates, more or less, in proportion to its quantity, and to the nature of those bodies. The expansion of water, even previous to its assuming the form of vapor, may be seen in an easy experiment. If a quantity of cold water, contained in a clear flask, is immersed in a vessel of boiling water; as the heat enters, the water in the flask will be seen to rise in the neck till it overflows. An iron rod a foot long being heated red hot, became 1-60 longer than before; and a glass cylinder, a fathom long, under the same circumstances, gained 1-50 in length. A metalline ring thus heated was increased 9-100 in its diameter; and a glass globe became extended 1-100 part by the heat of the hand only applied to its surface.[33] The _general_ effects of caloric are to increase the bulk of the substances with which it unites, and to render them specifically lighter than they were before; but in whatever quantity it is accumulated in bodies, it never adds to their absolute weight. Caloric favors the solution of salts, and promotes the union of many substances. In other cases it serves to separate bodies already united; so that in the hands of chemists it is the most useful and powerful agent with which they are acquainted. It is the cause of fluidity in all substances which are capable of becoming fluid, from the heaviest metal to the lightest gas. Let it be remembered that _all_ fluids are formed from solids by an addition of caloric; and that, by abstracting this caloric, solids would be reproduced. It insinuates itself among their particles, and invariably separates them in some measure from each other. We have reason to believe that every solid substance on the face of the earth might be converted to a fluid, or even a gas, were it submitted to the action of a very high temperature in peculiar circumstances.[34]