88 PLANT COMPOUNDS 



when purified, they frequently occur in nature as an exudate 

 mixed with gums and called Gum-resins, which emulsify 

 with water; with volatile oils called Oleo-resins, which are 

 softer than the resins proper; and with volatile oils together 

 with benzoic or cinnamic acid, in which case they are properly 

 called Balsams. 



78. Some of the Common Resins. — (a) Amber is a fossil 

 resin found mostly on the shore of the Baltic Sea, frequently 

 buried in the earth. It is the hardest resin known, varying 

 in color from yellow to black, sometimes clear and trans- 

 parent, sometimes cloudy. Chemically amber consists of 

 acids and esters. On heating in a retort above 287° C, it 

 melts and decomposes, forming water, succinic acid, a little 

 volatile fatty acid, oil of amber, and some other compounds. 

 The succinic acid and oil of amber are used in pharmacy. 

 Amber is used mostly for ornamental purposes, although 

 formerly it was employed in the manufacture of the more 

 expensive varnishes. 



(b) Colophony or Rosin is the solid residue remaining 

 after oil of turpentine (Section 76, h) has been distilled 

 off. It occurs naturally as an exudate with turpentine 

 from certain pine trees. It is a brittle, yellow to brown solid, 

 chemically consisting largely of an acid. It unites on boiling 

 with sodium or potassium hydroxide to form a deliquescent 

 substance called resinate used in making soaps and for sizing 

 paper. On fusing with manganese or with lead oxides it 

 forms resinates soluble in linseed oil and used as driers in 

 making varnish. On dry distillation colophony breaks 

 up into hydrocarbons, acids, and aldehydes. Commercially 

 two products are obtained — rosin spirit, boiling at 80° to 

 250° C. and rosin oil, boiling at over 300° C. Rosin spirit 

 is a colorless liquid composed of hydrocarbons, and resem- 

 bling oil of turpentine for which it is used as a substitute. 

 Rosin oil is a heavy, viscid liquid, colorless to brown, com- 

 posed mostly of high boiling point hydrocarbons. It is used 

 in making rosin-grease by mixing with milk of lime, for 

 lubricating axles, and for making printer's ink. Colophony 

 or rosin itself is used in making varnishes, in pharmacy, 

 and in the preparation of resinates, rosin spirit, and rosin oil. 



