CHEMISTRY. 



63 



Elements 



of 

 Chemistry. 



fharcoal 

 yields arti- 

 ficial tan- 



acid does not decompose it nor alter its properties. 

 This forms a marked distinction between natural and 

 artificial tannin. 



The alkalies unite with it, and prevent it from pre- 

 cipitating gelatine till they are saturated. The alka- 

 line earths, and mosi of the metallic oxides, form in 

 soluble compounds with it. Hence it precipitates 

 most of these bodies from their solutions. 



When distilled, artificial tannin yields water, a little 

 nitric acid, and a yellow coloured liquid; on raising 

 the fire, ammoniacal gas is disengaged with great ra- 

 pidity ; this is followed by carbonic acid gas, and a 

 gas possessing the properties of azote. A bulky 

 charcoal remains behind. From these results it is 

 obvious that this substance consists of oxygen, azote, 

 hydrogen, and carbon. The last constituent, no 

 doubt, predominates. 



Mr Hatchett has shewn that every charcoal, both 

 from animal and vegetable substances, provided it be 

 in the state of charcoal, yields artificial tannin when 

 digested with nitric acid. He has pointed out two 

 otner methods of procuring a substance possessed of 

 similar properties. The first is by dissolving indigo 

 and the resins, or gum resins, in nitric acid, and di- 

 gesting them for a considerable time in that liquid. 

 When the solution is evaporated to dryness, a yellow 

 coloured matter remains, which possesses the proper- 

 ties of artificial tannin. The second method is by 

 dissolving camphor and the resins in sulphuric acid, 

 digesting till the solution becomes black, and then 

 precipitating by pouring it into cold water. If the 

 black powder which falls be digested in alcohol, a 

 brown matter is taken up which possesses many of 

 the properties of artificial tannin. 



Seen are the properties of the colorific acids. 

 They act with most energy on metallic solutions, 

 forming precipitates which vary in their colour ac- 

 cording to the metal. It is this property which 

 renders them of so much importance in a chemical 

 point of view. The following Table exhibits a view 

 of the colours which these bodies strike with the 

 different metals, as far as is known. 



Table of 

 the colour* 

 which colo- 

 rific acidi 

 strike with 

 the metal-. 



Element* 



of 

 Chemistry. 



GHAP. VII. 



Of the Compounds of Chlorine. 



WE shall in this Chapter give an account of the _ 

 compounds which chlorine forms with all the other p, mn< i, o f 

 simple substances, as far as the subject has been in- chlorine, 

 vestigated. For all the experiments hitherto made 

 on the subject, we are indebted to Mr Davy, and his 

 brother, Mr John Davy. 



1. Chlorine lug the property of combining with with 

 oxygen. The compound is a gas of a yellow colour, oxygen, 

 winch may be obtained by pouring diluted muriatic 

 acid on the salt called hyperoxymuriate of potash, 

 and applying a moderate heat. The gas may be re- 

 ceived over mercury. It was discovered, and its pro- 

 perties invemgatrd, by Mr Davy, who has given it 

 the name of euchloric gas. Its colour is greenish yel- 

 low, and very intense. Water absorbs about ten 



