288 INDUSTRIAL PLANTS 
poor in oxygen and rich in hydrogen and carbon, very in- 
flammable, and, from their large proportion of carbon, burn- 
ing with a sooty flame. 
More or less resinous material is contained in the great 
majority of plants, and in many cases it is abundant. and 
valuable for use industrially. Rosin and copal, which are 
among the most important resins, will serve as typical ex- 
amples. 
Rosin is so much the most widely known of resinous ma- 
terials that it is commonly called ‘‘resin”’ as if it were the 
only substance to which that name could apply. Chemically 
it is known as colophony. It is one of the products obtained 
by distilling turpentine. What is properly called turpentine 
as already stated is the oleoresin which flows from wounded 
surfaces of pines and similar cone-bearing trees. When this 
is distilled the volatile parts that pass over and are con- 
densed form the familiar oil or spirits of turpentine, while 
the residue is rosin. The largest quantities are produced in 
our Southern States. Rosin is used as an ingredient in com- 
mon varnishes, is combined with tallow in cheap candles, 
and is extensively used in the making of yellow soap, inferior 
kinds of sealing-wax, and various cements. In shoemaker’s 
wax and certain medicinal plasters and ointments it enters 
as an important part. Musicians depend upon it to rosin 
the bows of stringed instruments, tin-men and plumbers 
use It as a flux in soldering, and it serves many other purposes 
in the industrial world. Its property of generating, when 
vigorously rubbed, that sort of frictional electricity called 
“resinous” has led to the use of rosin in certain forms of 
electric apparatus for experimental purposes. « 
Copal is aname applied rather indefinitely to a large variety 
of resins without much in common to distinguish them, but 
as strictly defined it is understood to include only such as 
occur naturally in hard masses resembling amber in appear- 
ance, and like that substance melting and dissolving only 
at a comparatively high temperature—a process requiring 
special precautions to prevent the resin and the solvent from 
catching fire. These resins make the best varnishes, and 
that is their main use. The botanical origin has long been 
- 
