can tell these things, but it cannot foretell the quality of the finished paint from a knowledge of the materials used.

""Chemistry is physics applied to atoms and molecules."—(Tyndall.) A chemical analysis applies to very small quantities of the substances used, and the accuracy of the results obtained from it depend entirely upon the method of sampling. When one considers that about all pigments are allotropic, that no two lots of paint liquids are exactly alike, and that any prepared paint changes more or less, in one way or another, with age, the chemist's test is proved to be of value in so far as it relates to the matter subject to his analysis and determinations, and no further.

The popular idea of a chemist is that of one who can analyze material substances and  determine  their  composition—that  is,