RESINS. 429 



Copal' is a singular kind of resin, said to be 

 obtained from a species of sumach (copallinum). 

 This tree is indigenous to some parts of North 

 America, and can be successfully cultivated even 

 in England; but it requires the heat of a tropical 

 sun to perfect its juice and cause spontaneous exu- 

 dation. This species of sumach does not grow 

 nearly so high as the other kinds. In Britain it 

 seldom attains to more than five feet in height, divid- 

 ing into many branches, which are garnished with 

 winged leaves composed of four or five pair of 

 narrow leaflets terminated by an odd one. They 

 are of a light green, but in autumn change to a purple 

 hue. The flowers are produced in loose panicles at 

 the ends of the branches. 



Copal appears in the form of a hard, shining, trans- 

 parent substance ; it is mostly of a lemon colour, 

 sometimes inclining to orange, but the best is of a 

 very light hue. It agrees with the other resins in 

 the property of combustibility, and all its external 

 characters, as well as in being insoluble in water ; but 

 it cannot be dissolved in alcohol, the essential oils, or 

 ether, without considerable difficulty. It holds in this 

 respect an intermediate state between the true resins 

 and amber ; resembling the resins by being soluble 

 in oily substances, which do not touch amber, and 

 resembling amber by greatly resisting the action of 

 alchol. It may be dissolved by digestion in linseed 

 oil, rendered drying by quicklime at a temperature 

 very little less than sufficient to boil or decompose 

 the oil. This solution, diluted with oil of turpentine, 

 forms a beautiful varnish, which, when properly applied 

 and gradually dried, is very hard and very durable. 

 The colour of the finest sort is so faint, that when 

 spread thinly over any surface it is not perceptible, 

 and only imparts a hard, smooth, transparent glazing. 



