enough to excite the desired interchanges and to form the new substance.

It is upon this sound theory that some combination paints are unwittingly made. If such paints are scientifically and honestly made, they are worthy of the utmost confidence, and we think they will ultimately displace all others.

TESTS

"Prove all things, hold fast that which is good."

Paint tests may be of three kinds; namely, Chemical, Mechanical, and Physical tests.

Chemical Tests.—In the selection of solids and liquids for paint-making, it is well to know that they contain no deleterious matter, such as soluble solids or destructive liquids, nor useless substances either to make  weight  or  to make bulk. Chemistry