(212) 
be regarded as turpentine, modified and rendered impure 
by partial burning. It is obtained from the same trees 
that yield turpentine, but the dead wood and stumps are 
preferred. The wood is stacked and so enclosed by earth 
as to partly exclude air, and is then fired at the top. As 
the wood burns above, the heat drives out the liquid tar 
just below, which runs off into vats and is stored in barrels. 
The charcoal powder which enters renders it black. A 
more perfect method is to distil it in suitable retorts. By 
subsequent distillation of the tar, oil of tar is driven off, 
naval pitch being left behind. Oil of tar contains, or yields 
a large number of valuable substances, such as Guaiacol, 
creosol, naphthalene, toluene, and xylene. In addition 
to the resins obtained from living kinds of trees, there are 
fossil resins of different degrees of hardness and color; 
these enter largely into the manufacture of varnishes. 
Varnish is a solution of one or more resins in some volatile 
liquid which, on evaporating, deposits a uniform and con- 
tinuous layer of the resin upon the surface to which the 
varnish was applied. Such a coating of varnish, if of good 
quality, is both hard and tough, hence not easily scratched, 
insoluble in water and waterproof, capable of taking a 
high polish, but melting and burning readily. Varnish 
resins differ in quality and value according to the degree 
an which the varnish made from them possesses the proper- 
ties named above. The best is probably anime copal. 
Not only is it so hard and tough as to stand floor-wear, 
but it is soluble in so few substances that the spilling of 
most liquids upon it will not injure it. Some of the trees 
yielding varnish resins are now almost or quite extinct, 
and the lumps of resin have lain buried in the soil in a 
fossil state since the age when these trees were living. 
Plant Constituents. Cases 63 to 68.—This exhibit con- 
sists of a series of alkaloids, acids, glucosides, amaroids, 
albuminoids, resinoids, and enzymes. These substances 
plants store up in their tissues, or in the tissues of one or 
more organs, and from them rey are extracted for use in 
all branches of the arts, sciences, and industries. 
