372 APPLIED SCIENCE 



ners" is legitimate and necessary. The thinning agent most 

 used in the paint trade is turpentine. 



416. Turpentine. The liquid known in the trade as 

 turpentine, or " turps," is obtained by the distillation of the 

 fluid exuded and collected from growing pines. It has a 

 strong smell, a bitter, disagreeable taste, and is a mixture of 

 hydrocarbons. Pine trees about forty years old, which have 

 been much exposed to the sun's rays, yield the most turpen- 

 tine. The bark of the tree is cut (wounded) in March, when 

 the sap begins to rise. The sap drips into a barrel placed 

 at the foot of the tree and is afterward purified by being al- 

 lowed to "settle " in the heat of the sun. The fluid filters into 

 the bottom of the barrel through a perforated false bottom. 



There are several kinds of turpentine, the best of which 

 comes from the south of France. Canada balsam is a vari- 

 ety obtained from a tree growing in the cold countries of 

 North America. China or Cyprus turpentine is brought 

 from the north of Africa, the south of Europe, and from islands 

 of the Mediterranean. All these turpentines on being dis- 

 tilled yield an essential oil which is commonly called spirit 

 of turpentine because it is the product of distillation. After 

 the oil of turpentine has been obtained, a hard, brown, brit- 

 tle residuum is left, which is known to commerce as rosin. 

 Rosin is highly inflammable, easily melted, insoluble in water, 

 and readily unites with oils. Cheaper liquids than tur- 

 pentine that will easily mix with oils, such as rosin, spirit, 

 shale-naphtha, benzine, and petroleum oils, are often used as 

 substitutes. 



417. Nature of Resins. Resins are gluelike bodies which 

 are found in plants or are produced by the oxidation of tur- 



