MANILA COPAL. 199 



leave an oily stain on paper, the glycerides must practically he entirely 

 decomposed. 



Furthermore, free glycerol is not soluble in cold linseed oil; hence 

 that which is formed must be removed, otherwise its separation would be 

 at least partly responsible for -the cloudiness of undercooked varnishes. 



According to Sabin, 28 ''Each varnish maker has his own secret methods for 

 treating the oil, which are probably all about alike. One of the most common 

 methods is to heat the oil from 260° to 288° for a very short time, which seems 

 to char certain impurities and coloring matter which settle out during the 

 subsequent tanking or storing which it receives." 



Gill, 29 referring to bleached oil, says that "it is prepared by special process kept 

 jealously guarded for the use of varnish makers. It may be prepared by heating 

 linseed oil hotter than in the preparation of "boiled oil," to 260° to 300°, or 

 by forcing oxygen through the oil." 



All fatty oils are decomposed above 250°, below this temperature they 

 are little changed, above it the change is greater the higher the temper- 

 ature. The products of the decomposition of neutral fatty oils, drying 

 or nondrying, contain acrolein, a decomposition product of glycerol, 

 hence free fatty acids must be formed. It is believed that one of the 

 disadvantages of heating linseed oil at the temperature employed in 

 varnish manufacture is the liberation of linoleic acid, which dries more 

 slowly than linolein. It would seem that the corresponding amount of 

 glycerol produced offers a more logical reason for the claims that oils 

 containing free acids remain tacky. 



EXPERIMENTAL. 



One hundred grams of raw .Manila copal were boiled with 200 cubic centimeters 

 of turpentine, in which this amount is only partially soluble, 100 cubic centimeters 

 of raw linseed were then added through the reflux condenser and the heating 

 continued with apparently no further solution. 



The experiment was repeated in the same manner with the exception that 

 the linseed oil contained 25 per cent by volume of oleic acid; upon continued 

 boiling a complete solution of the resin took place. 



A quantity of the mixed fatty acids of linseed oil was prepared and added in 

 varying proportions to raw linseed oil, depending upon the quantity of unmelted 

 resin it was desired to dissolve, and it was found that raw or boiled linseed oil, 

 containing the free, mixed, fatty acids of linseed oil in the proportions of 10 

 to 30 per cent calculated as oleic acid, formed homogeneous solutions with raw 

 or fused Manila copal when the latter is added in the proportion of 10 to 30 

 gallon varnishes and heated for a time at a maximum of 200°. When the tur- 

 pentine was added before the oil, the boiling point of turpentine, 155° to 165°, was 

 sufficiently high to effect complete solution with the exception of such foreign 

 matter as may be present in the resin. The subsequent addition of turpentine to 

 the oil and resin did not produce any cloudiness. 



!S hoc. tit., 72. 



"Oil Analysis. Philadelphia (1898), 86. 



