MANILA COPAL. 191 



those of the impure, high-melting resin acid obtained from the portion of 

 the original resin insoluble in alcoholic potash. 



The unsaponifiable matter does not melt, but chars at once upon the 

 application of direct heat, hence further examination of it was not made. 



Too much emphasis can not be placed upon the difficulties encountered 

 in a chemical examination of this class of substances. They are as 

 follows : First, their great susceptibility to atmospheric oxidation as 

 shown by Brooks 13 demands the avoidance of heat and undue exposure 

 to air and light; second, the tenacity with which the amorphous sub- 

 stances precipitated from aqueous solutions retain moisture when dried 

 under the imposed conditions; third, the possibility of isomeric forms of 

 the same substance; fourth, the tendency of resin acids to lactone or 

 other anhydride formation under the influence of heat and chemical 

 reagents; and fifth, the conversion of resin acids to neutral, oxygenated 

 bodies accompanied with a gradual lowering in potash value due to loss 

 of carbon dioxide. 



SUMMARY. 



It should be repeated that the experimental results obtained are not 

 considered sufficiently definite or extensive to warrant more than the 

 general conclusions that Manila copal consists essentially of free amor- 

 phous acids, a volatile hydrocarbon, a neutral saponifiable substance, 

 probably a lactone, and an unsaponifiable resin. 



Contrary to expectation, the free acids appear to bear no relation to 

 each other, or to the known resin acids of other coniferous resins. 



It should also be pointed out that the observations concerning the 

 resin acids of Manila copal herein recorded do not confirm those of 

 Tschirch and Koch for the resin acids of Dammara oricntalis Lamb. 



OLEOKESINOUS VARNISHES." 



In distinction from spirit varnishes, which are solutions of resin in 

 some volatile solvent such as turpentine, benzene, alcohol, etc., and from 

 plain oil varnishes which consist only of linseed or some other diying oil, 

 oleoresinous varnishes contain all the ingredients and partake of the 

 properties of both spirit and oil varnishes. 



The art of making oleoresinous varnishes has undergone no important 

 changes since the days of its first application. It consists essentially 

 now, as it did four hundred years ago, in combining resin, linseed oil, and 

 turpentine in such a manner as to produce a clear, homogeneous liquid. 

 Naturally, the simplest method of preparing such a varnish would be to 

 dissolve the resin in the drying oil in the right proportions to give the 

 desired effects of hardness and elasticity, and then to dilute the solution 

 with turpentine or some other volatile solvent to a consistency suitable 



"This Journal, Sec: A (1910), 5, 219. 



