MANILA COPAL. 197 



Andes ™ also refers to the use of linseed-oil acids in giving elacticity to spirit 

 varnishes and as a solvent for copals. 



Acting upon the above suggestions and from the knowledge that 

 substances of an acid nature such as alcohols, phenols, acetic acid, etc., are 

 much more efficient solvents for resin acids than neutral bodies like 

 petroleum ether, benzene, or esters, it was found that oleic, palmitic, and 

 linolic acids, either alone or in admixture, dissolved the resin acids of 

 Manila copal at moderate temperatures to clear, pale, amber-colored 

 solutions which remain so in the cold. Hence, an inquiry into the 

 nature of varnish oils and the changes which they undergo in the man- 

 ufacture of oleoresinous varnishes was considered important in its bearing 

 upon the subject under discussion. 



The first function of a vegetable oil as an ingredient of an oleoresinous 

 varnish is to serve as a vehicle or solvent to bring the resin into a 

 fluid condition and maintain it there. 



Any vegetable oil, such as coconut or cotton-seed oil, will fulfill this 

 function, but a solution of resin in these oils would never dry. The 

 second function of the vegetable oil is, therefore, to provide a solvent 

 which will dry and thus bind the particles of dissolved resin together in 

 a thin, elastic film; hence the so-called drying oils of which linseed oil 

 is the type have come into almost universal use for this purpose. 



Dismissing the various theories which have been advanced as to "why 

 and how oils dry," with the statement that because of their unsaturated 

 nature they are capable of absorbing large quantities of oxygen and that 

 by various means they may be rendered more siccative or drying, attention 

 will be called to the different preliminary treatments of linseed oil for 

 use in the arts and trades. 



According to Andes, 20 boiled linseed oil produced at any temperature below 

 230° can be used only for the grinding and thinning of paints or for application 

 alone. The varnish manufacturer requires boiled oil which has been heated to 

 at least 270°, so that all the foreign matters contained in the oil have been 

 removed. A difference must therefore be made between boiled oil intended for 

 paint and for varnish making. By foreign matters, Andes refers to mucilage and 

 the yellow pigment to which the color of raw linseed oil is due. 



Weger 21 makes the following remarks concerning linseed-oil "mucilage:" In 

 the manufacture of oil varnishes "varnish linseed oil" is used. By this term is 

 understood an oil which when rapidly heated to 280° to 320° does not "break," 

 i. e., does not separate any solid substances. If fresh, raw linseed oil be tested 

 by rapidly heating it in a test tube, a turbidity generally appeal's at 250°. 

 Ordinarily, commercial linseed oils (with the exception of "varnish oil," which 

 has undergone some chemical or mechanical treatment) almost always show this 

 coagulation upon rapid heating. • 



"Drying Oils, Boiled Oil, and Solid and Liquid Driers. London (1901), 68. 



20 Loc. tit., 174. 



21 Loc. tit., 125. 



