There remained a white, earthy solid, the weight of which was 15-1/2 grains.

Lavoisier had obtained 4-9/10 + 15-1/2 = 20-2/5 grains of solid; the pelican had lost 17-2/5 grains.

The difference between these weights, namely, 3 grains, was accounted for by Lavoisier as due to the solvent action of the water on the glass apparatus wherein it had been distilled, and on the glass basin wherein it had been evaporated to dryness.
Lavoisier's experiments proved that when distilled water is heated in a glass vessel, it dissolves some of the material of the vessel, and the white, earthy solid which is obtained by boiling down the water is merely the material which has been removed from the glass vessel.

His experiments also proved that the water does not undergo any change during the process; that at the end of the operation it is what it was at the beginning--water, and nothing but water.
By this investigation Lavoisier destroyed part of the experimental basis of alchemy, and established the one and only method by which chemical changes can be investigated; the method wherein constant use is made of the balance.
Lavoisier now turned his attention to the calcination of metals, and particularly the calcination of tin.

Boyle supposed that the increase in weight which accompanies the calcination of a metal is due to the fixation of "matter of fire" by the calcining metal; Rey regarded the increase in weight as the result of the combination of the air with the metal; Mayow thought that the atmosphere contains two different kinds of "airs," and one of these unites with the heated metal.
Lavoisier proposed to test these suppositions by calcining a weighed quantity of tin in a closed glass vessel, which had been weighed before, and should be weighed after, the calcination.