116 



C H E M I S 'I 1 K Y. 



Artificial 

 bitler prin- 

 ciple. 



How oh. 



In proper- 



"IV. !.!;i. 



cJ liquid ; and when concentrated, iron throw* dovm a 

 preen coloured precipitate. Indeed, it i almost at dc- 

 licate a test of iron a* tan and gallic acid. 



7. Muriate of tin throw* down a copious yellow pre- 

 cipitate. Thii precipitate, and that by iron, are soluble 

 in all acid*, but they lose their colour. 



8. Neither lime nor strontian water occasion any pre- 

 cipitate in the aqueous solution* of this substance ; but 

 barytes water occasions a brown precipitate. 



!>. Gelatine occasions no precipitate. 



III. The third species may be distinguished by the 

 name of artificial liilter principle, as it has been formed 

 by the action of nitric acid on various vegetable and ani- 

 mal substances. It was first obtained by Haussman, 

 while examining indigo, but he mistook its nature. Wei- 

 thcr afterwards formed it by digesting silk in nitric acid, 

 ascertained its properties, and gave it the name of yellow 

 bitter principle; he is therefore to be considered as the 

 real discoverer. Bartholdi afterwards procured it by 

 treating thewA/Vr willow with nitric acid. Mr Hatchctt 

 lately obtained it during his experiments on artificial tan- 

 nin, by treating indigo with nitric acid ; and about the 

 same time Fourcroy and Vauquelin procured it by the 

 same means, and examined its properties in detail. This 

 substance possesses the following properties : 



It* colour is a deep yellow, its taste intensely bitter. 

 It is soluble both in water and alcohol, and has the pro- 

 perty of dyeing silk, woollen cloth, and cotton, of a du- 

 rable yellow colour. It crystallizes in elongated plates, 

 and possesses many of the characters of an acid, com- 

 bining readily with alkaline substances, and forming cry- 

 Malliz.able salts. When potash is dropt into a concen- 

 trated solution of it, sir-all yellow prismatic crystals are 

 gradually deposited, consisting of bitter principle com- 

 bined with potash. These crystals were examined by 

 Wei thcr, but it was Fourcroy and Vauquelin that ascer- 

 tain: d their composition. They have a bitter taste, are 

 not altered by exposure to the air, are less soluble than 

 pure bitter principle. When thrown upon hot charcoal 

 they burn like gunpowder, and detonate very loudly 

 when struck upon an anvil, emitting a purple light. Am- 

 monia dropt into the solution of bitter principle deepens 

 its colour, and occasions J copious deposition of fine yel- 

 low spicular crystals. These are a combination of bitter 

 principle and ammonia. 



IV. Artificial tannin itself may be considered as ap- 

 proaching the bitter principle in many of its properties. 

 Its taste is always intensely bitter, and the colour of the 

 precipitates which it throws down from the metals, is si- 

 milar to what takes place when artificial hitter principle 

 11 present. It is indeed possible, that the bitter taste 

 may be owing not to the tannin, but to a portion of ar- 



..1 bitter principle, which may be always formed along 

 with the tannin ; but this has not been ascertained. It 

 M well known, that the bitter taste very easily overpowers 

 and conceals all other tastes. 



SECT. XVI. Of Tannin. 



Notwithstanding the numerous experiment* made upon 

 the infusion of nutgalls, we arc not in possession of a 

 process capable of furnishing tannin in a state of purity. 

 Hence the obscurity which btill hangs over its charac- 

 ter*. The properties of thi substance, as far as known, 

 and the different methods of procuring it hitherto pro- 

 poted by chemists, have been detailed in a preceding 

 part of this article. 



Like mo*t other vegetable substances, it seems to be 

 tuioepuble of different modifications. The following 



Chemical 

 Nature. 



are the different specie* of tannin which have been hi- 

 therto noticed : 



1. Tannin from nutgalls. This ia the common speow 

 descril>ed in this article under ' !" tannin. It pre- 



cipitates iron black, and form* a firm insoluble brown 

 precipitate with glue. The hark of oak, and most other 

 astringent trees in this country, arc supposed at present tannin, 

 to contain this specie* of tannin. 



'2. The tannin which constitutes so large a proportion 

 of catechu forms the second species. Its peculiar na- 

 ture was first observed by Proust. It was afterwards 

 more particularly examined by Mr Davy. It forms with 

 iron an olive coloured precipitate. 



3. The tannin of kino constitutes a third species. This 

 substance is obtained from different vegetables. It was 

 originally imported, as is supposed, from Africa ; but at 

 present the common kino ot the shops is, according to 

 Dr Duncan, an extract from the coccoloLn urijera, or 

 mi-AiV/r grajic, and is brought chiefly from Jamaica. 

 But the finest kino is the product of different species ot 

 (itctitypitts, particularly the resinifera, or brown gum- 

 tree of Botany Bay. It is an astringent substance of a 

 dark red colour, and very brittle. It dissolves better in 

 alcohol than water. The solution in the latter liquid is 

 muddy ; in the former transparent, arid z fine crimson if 

 sufficiently diluted. It throws down gelatine of a rose 

 colour, and forms with salts of iron a deep green preci- 

 pitate, not altered by exposure to the air. 



4. The fourth variety of tannin is contained in sumach. 

 This is a powder obtained by drying and grinding the 

 shoots of the rhus coricriu ; a shrub cultivated in the 

 southern parts of Europe. The tan, which it contain* 

 in abundance, yields a precipitate with gelatine, which 

 subsides very slowly, and remains in the btate of a white 

 magma withcv.it consistence. 



5. The fifth variety, according to Proust, is to be 

 found in the wood of the moms tincloria, or old fustic, 

 as the British dyers term it. This wood gives out au 

 extract both to alcohol and water, which yields a preci- 

 pitate with gelatine. A solution of common salt is suf- 

 ficient to throw it down. 



SECT. XVII. Of the Extractive Principle. 



The word extract was at first applied to all those sub- Extractive 

 stances which were extracted from plants by means of principle, 

 water, and which remained behind in the state of a dry 

 mass when the water was evaporated ; consequently it 

 included gum, jelly, and several other bodies. But, of 

 late, it has been confined by many to a substance which 

 exists in many plants, and which may be obtained near, 

 ly in a state of purity, according to Hermbsladt, by in- 

 fusing saffron in water for some time, filtrating the in- 

 fusion, and evaporating it to dryness. But as the word 

 extract occurs even in modern authors in its original 

 sense, we shall rather denote this substance by the phrase 

 extractive principle, to prevent ambiguity. 



The difficulty of obtaining the extractive principle in 

 a separate state, and the facility with which it alters itj 

 nature, have hitherto prevented chemists from exami- jfc 

 ning it with that attention to which it is entitled. It 

 was first particularly attended to by Rouelle ; but it is 

 to Fourcroy and Vauquelin that we are chiefly indebt- 

 ed for ascertaining its characters. The dissertation of 

 Vauquelin, in the Journal dcl'harmack, is by tar the best 

 account of extractive matter which has hitherto appear- 

 ed. Many valuable facts and curious observations were 

 published by Hermbstadt, also, in hi dissertation on ex- 

 tract. But, uufortuuately, the term hai not been al- 



