liberated on the combustion of 6 times that amount.

A further example of the difference between quantity of heat and sensible
temperature may be seen in the combustion of coal, for (say) one
hundredweight of that fuel might be consumed in a very few minutes in a
furnace fitted with a powerful blast of air, the operation might be
spread over a considerable number of hours in a domestic grate, or the
coal might be allowed to oxidise by exposure to warm air for a year or
more. In the last case the temperature might not attain that of boiling
water, in the second it would be about that of dull redness, and in the
first it would be that of dazzling whiteness; but in all three cases the
total quantity of heat produced by the time the coal was entirely
consumed would be absolutely identical. The former experiment with water
and a gas-burner, too, might easily be modified to throw light upon
another problem in acetylene generation, for it would be found that if
almost any other liquid than water were taken, less gas (_i.e._, a
smaller quantity of heat) would be required to raise a given weight of it
from a certain low to a certain high temperature than in the case of
water itself; while if it were possible similarly to treat the same
weight of iron (of which acetylene generators are constructed), or of
calcium carbide, the quantity of heat used to raise it through a given
number of thermometric degrees would hardly exceed one-tenth or one-
quarter of that needed by water itself. In technical language this
difference is due to the different specific heats of the substances
mentioned; the specific heat of a body being the relative quantity of
heat consumed in raising a certain weight of it a certain number of
degrees when the quantity of heat needed to produce the same effect on
the same weight of water is called unity. Thus, the specific heat of
water being termed 1.0, that of iron or steel is 0.1138, and that of
calcium carbide 0.247, [Footnote: This is Carlson's figure. Morel has