The experiments have been made with the vapors of two very volatile
liquids, namely, sulphuric ether and hydride of amyl. The sources of
radiant heat were, in some cases, an incandescent lime cylinder, and in
others a spiral of platinum wire, heated to bright redness by an
electric current. One or two of the measurements will suffice for the
purposes of illustration. First, then, as regards the lime light; for 1
inch of pressure in the long tube, the absorption was 18.4 per cent. of
the total beam; while for 3.5 inches of pressure in the short tube, the
absorption was 18.8 per cent., or almost exactly the same as the former.
For 2 inches pressure, moreover, in the long tube, the absorption was
25.7 per cent.; while for 7 inches in the short tube it was 25.6 per
cent. of the total beam. Thus closely do the absorptions in the two
cases run together--thus emphatically do the molecules assert their
individuality. As long as their number is unaltered, their action on
radiant heat is unchanged. Passing from the lime light to the
incandescent spiral, the absorptions of the smaller equivalent
quantities, in the two tubes, were 23.5 and 23.4 per cent.; while the
absorptions of the larger equivalent quantities were 32.1 and 32.6 per
cent., respectively. This constancy of absorption, when the density of a
gas or vapor is varied, I have called "the conservation of molecular
action.
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