VOLATILE OILS AND RESINS 91 



leaf pine, in the United States. This material is collected 

 in boxes made in the trees or better in cups hung on tin- 

 trees. Fig. 21 shows the best modern method for collecting 

 crude turpentine. The first year's flow called 'virgin dip" 

 is the best. "Yellow dip" is the yield of subsequent years, 

 and "scrape" is the hardened material which is scraped from 

 the trees. This last is the poorest of all. The crude tur- 

 pentine is placed in copper stills and distilled with steam to 

 separate the volatile oil of turpentine (Section 76, /."). Colo- 

 phony or rosin is left in the still (Section 78, b). The 

 oleo-resin itself has no value except as a source of oil of 

 turpentine and rosin. Fig. 22 illustrates the distillation 

 of turpentine. 



(d) Tolu comes from South America as a nearly solid 

 mass, yellow-brown in color, of aromatic odor and taste. It 

 contains both benzoic and cinnamic acids, probably united 

 with resin alcohols, and in addition a few other compound-. 

 It is largely used in medicine. 



81. Compounds Similar to the Resins. — (a) Rubber or 

 Caoutchouc. — Many trees contain besides the so-called sap 

 and other liquids, a milky juice called latex, flowing in 

 special elongated cells or tubes. The function of this latex 

 may be to carrv food material in an emulsified form, or to 

 serve as a protection when the tree is wounded. It oozes 

 out of cut surfaces, hardens on exposure to the air, and 

 serves to keep out water and bacteria just as do the 

 resins (Section 77). This latex is an emulsion of fats, waxes, 

 resinous substances, and proteins in a watery fluid. Certain 

 trees, more particularly in South America, contain in the 

 latex minute liquid drops of a hydrocarbon, having the 

 general formula of a terpene, (\oHi 6 , but supposed to be a 

 chain compound and not a ring compound like a terpene. 

 These drops coagulate on exposure to the air. In practice 

 this coagulation is hastened by the smoke of burning palm- 

 nuts, or by the addition of salt water, wood-ash lye, or alum. 

 The resulting mass forms the crude rubber of commerce. 

 To obtain the latex the trees are cut and the latex gathered 

 much as is maple sap in the United States. The pure hydro- 

 carbon is nearly white when fresh but darkens on exposure 



