CHEMISTRY. 



115 



Chemical When the juice of the papaw is treated with water, 



Examina. t j, e greatest part dissolves ; but there remains a substance 

 insoluble, which has a greasy appearance. It softens in 



. _ _\ the air, and becomes viscid, brown, and semitransparent. 



When thrown on burning coals, it melted, let drops of 

 grease exude, emitted the noise of meat roasting, and 

 produced a smoke which had the odour of fat volatilized. 

 It left behind it no residue. This substance was the 

 Jibrin. The resemblance between the juice of the papaw 

 and animal matter is so close, that one would be tempt- 

 ed to suspect some imposition, were not the evidence 

 that it is really the juice of a tree quite unexceptionable. 

 The properties of fibrin are the following : 



Improper- 1. It is tasteless, fibrous, elastic, and resembles glu- 

 tie*. ten. 



2. It is insoluble in water and in alcohol. 



3. It is not dissolved by diluted alkalies. 



4. But acids dissolve it without difficulty. 



5. With nitric acid it gives out much azotic gas. 



6. When distilled it yields much carbonate of ammo- 

 nia and oil. 



7. It soon putrefies when kept moist, becomes green, 

 but does not acquire any resemblance to cheese. 



SECT. XV. Of the Bitter Principle. 



Bitter Many vegetable substances have an intensely bitter 



principle, taste, and on that account are employed in medicine, by 

 brewers, &c. This is the case with the wood of the 

 quassia amara and exce/sa, the common quassia of the 

 shops ; with the roots of the gentiana lutea, common 

 gmtian ; the leaves of the humiilus lu/m/us, or hop; the 

 bark and wood of tfce spintinm scoparium, or common 

 broom ; the flowers and leaves of the anl/temit nobilis or 

 ch-nnomUe ; and many other substances. Some of these 

 bodies owe their bitter taste to the presence of a pecu- 

 liar vegetable substance differing from every other, which 

 may be distinguished by the name of the bitter principle. 

 No chemical examination of this substance has been 

 hitherto published ; nor, indeed, are we in possession of 

 any method of separating it from other bodies, or of 

 ascertaining its presence. At the same time, it cannot 

 be doubted that it possesses peculiar characters; and its 

 action on the animal economy renders it an object of im- 

 portance. 



How ob- ! W' en water is digested over quassia for some time, 



tained. it acquires an intensely bitter taste, and a yellow colour, 

 but no smell. Wlien water thus impregnated is evapo- 

 rated tu dryness in a low heat, it leaves a brownish-yel- 

 low substance, which retains a certailf degree of trans jja- 

 rency. It continues ductile for some time, but at last 

 becomes brittle. This substance we shall consider as the 

 bitter principle in a state of purity. It it contains any 

 foreign body, it must be in a very minute proportion. 

 This substance was found by the writer of this article to 

 pos-esi the following properties : 



In pro- 1. Its taste is intensely bitter. Colour brownish-yel- 



pertiei. low. 



2. When heated, it softens, and swells, and blackens ; 

 then burns away without flaming much, and leaves a 

 sm ill quantity of ashes. 



3. Very soluble in water and alcohol. 



4. Does not alter the colour of infusion of litmus. 



.5. Lim--- water, barytes-water, and strontian water, oc- 

 casion no precipitate. Neither is any precipitate thrown 

 down by tilicaled potash, aluminated potash, or sulphate 

 of magnesia. 



6. The alkalies occasion no change in the diluted so- 

 lution of the bitter principle. 



Chemical 

 U lamina- 

 tion of 

 Nature. 



7. Oxalate of ammonia occasions no precipitate. 



8. Nitrate of silver renders the solution muddy, and a 

 very soft flaky yellow precipitate falls slowly to the bot 



torn. s^-y-.*' 



9. Neither corrosive sublimate nor nitrate of mercury 

 occasion any precipitate. 



10. Nitrate of copper, and the ammonial solution of 

 copper, produce no change ; but muriate of copper gives 

 the white precipitate, which falls when this liquid salt is 

 dropt into water. 



11. Sulphate and oxymuriate of iron occasion no 

 change. 



12. Muriate of tin renders the solution muddy, but 

 occasions no precipitate, unless the solution be concen- 

 trated ; in that case a copious precipitate falls. 



13. Acetite of lead occasions a very copious white 

 precipitate ; but the nitrate of lead produces no change. 



14. Muriate of zinc occasions no change. 



15. Nitrate of bismuth produces no change, though 

 when the salt is dropt into pure water a copious white 

 precipitate appears. 



16. Tartar emetic produces no change ; but when the 

 muriate of antimony is used, the white precipitate ap- 

 pears, which always falls when this salt is dropt into 

 pure water. 



17. Muriate and arscniate of cobalt occasion DO 

 change. 



18. Arseniate of potash produces no effect. 



19. Tincture of nutgalls, infusion of nutgalls, gallic 

 acid, occasion no effect. 



These properties are sufficient to convince us that the 

 bitter principle is a substance differing considerably from 

 all the other vegetable principles. The little effect of 

 the different re-agents is remarkable. Nitrate of silver 

 and acetate of lead are the only two b, dies which tkrow 

 it down. This precipitation cannot be ascribed to the 

 presence of muriatic acid ; for if muriatic acid were pre- 

 sent, nitrate of lead would also be thrown down. 



II. Besides this purest species of bitter principle, it is Another 

 probable that several others exist in the vegetable king species of 

 dom, gradually approaching by their qualities to the na- bitter prin- 

 ture of artificial laiinin. The second species is disrin- c 'P le - 

 gtiished from the preceding, by the property which it 

 has of striking a green colour with iron, and of precipi- 

 tating that metal trom concentrated solutions. MrChe- 

 nevix separated a portion of it from coffee by the fol- HOW ob- 

 lowing process : He digested unburnt coffee in water, taiaed. 

 and tillered the liquid. It was then treated with muriate 

 of tin. The precipitate was edulcorated, mixed with 

 water, and treated with sulphuretcd hydrogen gas. The 

 tin was thus precipitated, and the substance with which 

 it had been combined was dissolved by the water. The 

 liquid was then evaporated to dryness. The substance 

 thus obtained possessed the following properties: 



1. S< mitransparent like horn, and of a yellow colour. j tt propcr . 



2. When exposed to the air it does not attract mois- u cs . 

 ture. 



3. Soluble in water and in alcohol. The solution in 

 water is semitransparent, and has a j leasant bitter taste. 

 When the alkaline solutions are dropt into it, the colour 

 becomes garnet red. 



4. It is not precipitated from water by the alkaline 

 carbonates. Sulphuric acid renders the solution brown, 

 but produces \M further change. Neither muriatic acid, 

 nor phosphoric acid, nor the vegetable acids, produce 

 any change on this solution. 



5. The muriates of gold, platinum, and copper, occa- 

 sion no change. 



6. With solutions of iron it forms a fine green colour- 



