472 RESINS 



After the secretion of the resin the twigs are broken off, and form 

 without further preparation the stick lac of commerce. Stick lac 

 therefore consists of the twigs of the trees coated with a granular 

 brownish or reddish resin which is frequently 7 mm. thick. Enclosed 

 in this resin are the bodies of the insects, which contain a valuable 

 colouring matter. The latter is extracted by breaking the lac from 

 the twigs, crushing it, and exhausting it with water and sometimes 

 subsequently with dilute soda solution. The aqueous solution contains 

 a red colouring matter, laccaic acid, allied to, but not identical with, 

 carminic acid ; it is evaporated to dryness, and the residue, pressed 

 into cakes, constitutes the lac dye of commerce. After the resin 

 has been crushed and freed from colouring matter, it is spread out 

 on floors to dry and bleach ; it then forms brownish grains which are 

 known as seed lac. This still contains various debris of the insects, &c. 



It is melted with a little orpiment and resin (2 to 5 per cent.) and 

 pressed whilst hot through a cloth. The strained lac thus obtained is 

 spread into sheets about 3 mm. thick which are softened by heat and 

 stretched to thin sheets. These sheets, broken up and sorted, con- 

 stitute the shellac of commerce. Garnet lac is a dark coloured variety, 

 and button lac is in the form of thin discs. 



Lac is prepared in various parts of India, particularly in Bengal 

 and Assam, and is exported chiefly from Calcutta. 



Description. Shellac usually occurs in thin, brittle, translucent, 

 leafy flakes devoid of odour and taste. The colour varies from brownish 

 yellow (orange shellac) to deep reddish brown (garnet shellac), the 

 palest being considered the best. It melts when heated, evolving a 

 characteristic odour. 



Constituents. A recent investigation of stick lac (Farner, 1899) 

 resulted in the separation of the following constituents : 



Wax . . . . . . . . . 6'0 per cent. 



Colouring matter (laccaic acid) .... 6'5 



Resin 74-5 



Residue (sand, vegetable and animal debris) . . 9'5 

 Moisture and loss ....... 3'5 



Of the resin 35 per cent., composed principally of fatty acids, was 

 soluble in ether containing alcohol. The part insoluble in ether 

 (65 per cent.) consisted of a resinotannol combined with aleuritic acid, 

 a crystalline acid belonging to the fat acid series. A colouring matter 

 erythrolaccin, crystallising in golden yellow crystals, is also present. 



Shellac consists principally of the resin (90 per cent.) and wax and 

 other substances (10 per cent.) Orpiment, although used in its pre- 

 paration, seldom occurs in shellac. Adulteration with colophony 

 may be detected by dissolving in alcohol, precipitating the resin with 

 water, filtering, drying, and digesting with petroleum spirit ; if 



