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We shall have to seek the exact meaning
which ought to be given to the experiments on the emanation of these
bodies, and to discover whether these experiments really imperil the
law of Lavoisier.
For some years different experimenters have also effected many very
precise measurements of the weight of divers bodies both before and
after chemical reactions between these bodies. Two highly experienced
and cautious physicists, Professors Landolt and Heydweiller, have not
hesitated to announce the sensational result that in certain
circumstances the weight is no longer the same after as before the
reaction. In particular, the weight of a solution of salts of copper
in water is not the exact sum of the joint weights of the salt and the
water. Such experiments are evidently very delicate; they have been
disputed, and they cannot be considered as sufficient for conviction.
It follows nevertheless that it is no longer forbidden to regard the
law of Lavoisier as only an approximate law; according to Sandford and
Ray, this approximation would be about 1/2,400,000.


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