SHELLAC 473 



colophony is present the petroleum spirit solution will assume an 

 emerald-green colour when shaken with a O'l per cent, aqueous solution 

 of cupric acetate. The presence of colophony is also indicated by the 

 iodine value which should not exceed 12 in pure shellac (colophony 

 136 to 180). 



Bleached shellac is made by dissolving shellac in hot solution of 

 sodium carbonate and adding chlorinated lime, which forms chlori- 

 nated soda and deposits calcium carbonate. The resin is then pre- 

 cipitated, collected, ' pulled ' under water, twisted into sticks, and 

 kept under water. 



Uses. Shellac is largely used in varnishes, but is not employed 

 medicinally. 



The following resins are largely used for various technical purposes : 



Zanzibar copal (gum animi) ; from Trachylobium Hornemannianum, 

 Hayne, (N.O. Leguminosce) ; a fossil resin dug up on the East Coast of 

 Africa ; varies much in size ; pale yellow to deep reddish- brown or 

 greenish-red ; transparent or semi-transparent ; surface warty or 

 longitudinally striated ; consists chiefly of trachylolic acid (80 per cent.) 

 isotrachylolic acid and resene. 



American copal, from Hymencea Courbaril (Brazil), Linne ; pale 

 brown transparent and brittle, of agreeable odour. 



Australian copal (gum Kauri) ; from Agathis australis, Stender ; 

 mostly fossil, pale yellow or greenish yellow, conchoidal vitreous 

 fracture, balsamic odour. 



West African copal ; from Copaifera Guibourtiana, Benth. 



Manilla copal (=East Indian Dammar) ; from Dammora orientalis, 

 Lambert (N.O. Coniferce) ; fragments of large masses ; yellow, slight 

 but distinctly aromatic odour. 



The copals are entirely soluble in alcohol, but only partially in 

 benzene, chloroform, &c. 



Dammar, probably from a species of iShorea (N.O. Dipterocarpece) ; 

 imported from Singapore ; pale yellow, transparent or translucent 

 nodules or stalactitic masses coated with white powder ; fracture 

 vitreous, often exhibiting air bubbles. 



Gum accroides (grass- tree gum ; black-boy gum), from Xanthorrhoea 

 hastilis, Robert Brown, and X. australis, Robert Brown (N.O. Liliacece, 

 Australia). The resin of the former is yellow and contains xanthore- 

 sinotannol combined with paracumaric acid, and also free para- 

 cumaric and cinnamic acids ; that of the latter is red and contains 

 erythroresinotannol combined with paracumaric acid, free para- 

 cumaric acid but no cinnamic acid. The resin is a natural exuda- 

 tion covering the stem and leaf bases of the plant. 



