214 • BROOKS. 



THE FORMATION OF COPAL OIL AT TEMPERATURES ABOVE 320°. 



The formation of copal oil is much more rapid at a temperature of 

 320° or above, than it is at 300°. Between 320° and 360° large quantities 

 of oil distill from the melt. 



Many resins may be melted with very large proportions of oil from 

 colophony or copal and yet solidify to hard masses. Residues from 

 vacuum distillations, which contain very little or no copal oil, are quite 

 brittle. The addition of copal oil makes the mass tougher. 



A sample of Manila copal was melted with an equal weight of copal oil. On 

 cooling to 30° the mass became sufficiently hard to break with a conchoidal 

 fracture when struck a sharp blow. Synthetic mixtures containing 25 per cent 

 of copal oil are quite hard at ordinary temperatures. 



Copal oil is miscible in all proportions with absolute ethyl alcohol, 

 amyl alcohol, acetic acid, acetone, ether, chloroform, ligroin, benzene, 

 turpentine, and linseed oil. When a clear, concentrated solution of 

 heated copal in one of these solvents is partially precipitated by diluting 

 with the same solvents, the copal oil is left in solution together with 

 some resinous substances, while the precipitated portion is free from 

 copal oil. The effect of removing the copal oil in this manner is shown 

 by the folloAving experiments. 



A sample of Manila copal weighing 500 grams was melted in a covered iron 

 vessel and the temperature maintained at about 320° to 325° for one-half hour. 

 The loss in weight after this treatment was 25.0 per cent. ::s A portion of this 

 melted sample weighing 50 grams was remelted, the temperature not rising above 

 220°, and 71 grams of hot boiled linseed oil, which had previously been tested for 

 purity, was stirred in. These proportions correspond to the composition of a 

 10-gallon varnish, the calculation being based on the weight of the unheated 

 resin. When all of the oil had been added, a drop test showed no cloudiness and 

 a small test tube sample remained clear on cooling. When the 'solution had 

 cooled to 170°, 25 cubic centimeters of turpentine were added. A sample of 

 this mixture also remained clear after cooling. 



This experiment was performed for the sake of comparison with the 

 following : 



A portion of the same melted sample weighing 100 grams was completely 

 dissolved in 100 cubic centimeters of benzene. The resin was then partially pre- 

 cipitated by adding 800 cubic centimeters of ligroin. The solvent was decanted 

 from the precipitate and eva.poA.ted on the steam bath and finally over a free 

 flame until the temperature of the mass had risen to 180° and all of the solvent 

 had been expelled. The residue weighed 65 grams and evidently contained a 



31 A large part of this loss in weight represents volatile oils. Obviously, the 

 loss in weight accompanying a given amount of decomposition will depend more 

 or less on the form of the containing vessel and the manner of heating. I venture 

 the opinion that the old drop test gives a more accurate indication of the point 

 beyond which further heating is unnecessary than any arbitrary rule such as 

 heating until a certain per cent of weight is lost. 



