288 INDUSTRIAL PLANTS 



poor in oxygen and ricli in hydrogen and carbon, very in- 

 flammable, and, from their laige 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 w^re the 

 only substance to which that name could apply. Chemicall}' 

 it is known as colophony. It is one of the products obtained 

 by distilling turpentine. What is properl}- called turpentine 

 as already stated is the oleoresin which flow^s 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 a name 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 



