1*4 



CHEMISTRY. 



Kr, Mr Saunders, and Dr Roxburgh. Though very 

 often i m ployed in the arts, it was neglected by ctWmiits. 

 Mr Hatchttt hi lately rxamimd it it'n hii usual ad- 

 dr, and ascertained lU composition a;. 



There are various kmdt of lac dutlnguhrd in com- 

 merce. Stick lac it the tubstance : ural state, 

 :mg unall twig*. When broken off and boiled in 

 water, it lose* its , and is called teed lac. 

 When melted ind rrduc< d to the state of thin crust, it 

 ii called sMl lac. Stick lac is of a deep red colour, and 

 yields to water a substance which is used a* a red dye. 

 The other two varieties are brown. 



Water dissolve* the greatest part of the colouring 

 matter of lac, which varies from 15 to ij per cent. Alco- 

 hol dissolves the greatest part of the resin, which con- 

 stitutes the chief ingredient in the composition of lac. 

 Ether acts more feebly. Sulphuric acid dissolves and 

 gradually chars lac ; nitric acid dissolves, and then pro- 

 duces the same changes on it at on other resinous bodies. 

 Muriatic and acetic acids likewise act as solvents. A 

 solution of borax in water readily dissolves lac. The 

 best proportions are 20 grains of borax, 100 grains of 

 lac, and four ounces of water. This solution, mixed 

 with lamp black, constitutes Indian ink, and may indeed 

 be employed for many of the purposes of varnish. The 

 fixed alkalies readily dissolve lac, but not the volatile. 

 When placed oil a hot iron it melts, and emits a thick 

 iinoke with an odour rather plca&ant, leaving a spongy 

 coal. When distilled, it yields water slightly acidulous, 

 and a thick butyraceous oil. The gases emitted are a 

 mixture of carbonic acid and carbureted hydrogen. Slick 

 lack yields also some carbonate of ammonia ; but the 

 other two varieties none. The following Table exhibits 

 the constituents of the different varieties of lac, accord- 

 ing to the analysis of Mr Hatchett. 



The resin is lest brittle than those bodies usually are. 

 The colouring matter possesses the properties of extrac- 

 tive ; the wax is analogous to myrtle wax, and the glu- 

 ten closely resembles the gluten of wheat. 



Amber. 11. Anther. This substance is undoubtedly of vege- 



table origin ; and though it differs from resins in some 

 of its properties, yet it agrees with them in so many 

 others, that it may, without impropriety, be referred 

 to them. 



Amber is a brittle, light, hard substance, usually 

 nearly transparent ; sometimes nearly colourless, but 

 commonly yellow or even deep brown. It has consider- 

 able lustre. Its specific gravity is 1.065. It is tasteless, 

 and without smell, except when pounded or heated, 

 when it emits a fragrant odour. When heated it sof- 

 ten*; but, as far as is known, cannot be melted without 

 losing tome of its weight, and altering its appearance. 

 In a strong heat it burns leaving a small quantity of 

 ashes, the nature of which has not yet been ascertain- 

 ed. Water has no action on it ; but alcohol, by long 

 digestion, dissolves about one eighth of the amber, and 

 formt a coloured solution, which, when concentrated, 



tion of 

 N.I. urr. 



becomes milky when mixed with water. Trie residu- 

 um of the amber is not acted on by alcohol. Though 

 ntnlwr br roasted before the action of the alcohol, the 



tincture is still formed. Hence we learn that the re- _ 



sinous part of amber is not expelled by a melting lie.it. 



The weaker acids hare no action on amber. Sulphu- 

 ric acid converts it into a black resinous mass. Nitric 

 acid acts upon it ; when assisted by heat, nitrous gas ii 

 emitted. 



Neither fixed nor volatile oils have any action on am- 

 ber unless it has been previously roasted or exposed to 

 a melting heat. When thus treated, it combines with 

 oils, and the solution forms amber varnith. The process Amhcr 

 recommended by Ny-trom is this : Amber is to be varnith. 

 spread on a flat -bottomed iron pan, and placed on an 

 equal coal fire till it melt ; it is then to be withdrawn, 

 covered with a plate of copper and iron, and allowed to 

 cool. 1 f the process be properly conducted, the amber 

 will have lost half of its weight. If the fire be too 

 strong, the amber will be scorched and rendered useless. 

 If it be too low, the amber will not melt, but be re- 

 duced to a brown crust, which answers well enough 

 for a varnish, provided it be exposed to heat till it is re- 

 duced to one half of the original weight. One part of 

 this roasted amber is to be mixed with three parts of 

 the linseed oil (rendered drying by litharge and white 

 vitriol,) and the mixture exposed to a gentle heat till 

 the amber is dissolved : it is then to be withdrawn from 

 the fire, and when nearly cold, four parts of oil of tur- 

 pentine are to be added. The whole is then allowed 

 to settle, and the clear portion is passed through a linen 

 cloth. 



SECT. XXIV. OfGuaiacvm. 



This substance is obtained from the guaiacum offici- Guaiacura, 

 nale, a tree which is a native of the West ladies, and 

 yields a very hard heavy wood. The resin exudes spon- HOW ob- 

 taneously, and is also driven out artificially, by heating rained, 

 one end of the wood in billets previously bored longitu- 

 dinally ; the melted resin runs out at the extremity far- 

 thest from the fire. This substance has been used in 

 medicine for a considerable time, having been originally 

 recommended in venereal diseases. Nothing it known 

 concerning its original introduction into Europe. 



It was considered by chemists as a resin, till Mr Hat- 

 chett observed, that when treated with nitric acid it 

 yielded products very different from those of the resi- 

 nous bodies. This induced Mr William Brande to ex- 

 amine its chemical properties in detail. 



Guaiacum is a solid substance, resembling a resin in [ [5 proper- 

 appearance. Its colour differs considerably, being part- tie*, 

 ly brownish, partly reddish, and partly greenish ; and 

 it always becomes green when left exposed to the light 

 in the open air. It has a certain degree of transparency, 

 and breaks with a vitreous fracture. When pounded it 

 emits a pleasant balsamic smell, but has scarcely any 

 taste, although when swallowed it excites a burning sen. 

 sation in the throat. When heated it melts, and diffuses 

 at the same time a pretty strong fragrant odour. Its 

 specific gravity is 1.2289. 



When guaiacum is digested in water, a portion of it is 

 dissolved, the water acquiring a greenish brown colour, 

 and a sweetish taste. The liquid, when evaporated, 

 leaves a brown substance, which possesses the property 

 of extractive. 



Alcohol dissolves guaiacum with facility, and formt a 

 deep brown-coloured solution. Water renders this solu- 

 tion milky by epating the resin. Muriatic acid throws 



