248 



©N VEGETABLE ASTRINGENTS. 



fluenced by the relative quantities in which its ingredients 

 are presented to each other. When there is an excess either 

 of jelly or of tan, the precipitate subsides more slowly, and 

 is of a softer texture, Beside jelly, rhatany is precipitated 

 by oximuriate of tin, oxisulphate of iron, acetate of lead, 

 tartarized antimony, nitromuriate of gold and of platina, 

 {ilura, lime, and sulphuric acid. The oximuriate of tin 

 throws down a dense precipitate, but only in moderate 

 quantity much less than that produced by jelly ; the oxi- 

 sulphate of iron produces a black precipitate, which speedi- 

 ly subsides to the bottom of the vessel ; acetate of lead in- 

 stantly combines with all the contents of the solution, throws 

 them down in the form of a pink mass, and leaves the fluid 

 transparent and colourless ; antimony throws down a small 

 quantity of a reddish powder ; the nitromuriate of gold 

 produces a very copious dark purple precipitate, and the 

 nitromuriate of platina an equally copious one of a reddish 

 brown colour. Alum renders the solution turbid, changes 

 its colour to a dirty brown, and throws down a small quan^ 

 tity of precipitate; lime water heightens the colour, and 

 produces a red precipitate; and sulphuric acid produces 

 a copious precipitate of a light red colour. Carbonate of 

 potash converts the colour of the solution to a deep blood 

 yed, but produces no farther effect. After the infusion of 

 rhatany has had jelly added until no further precipitation is 

 produced, the oximuriate of tin renders it slightly turbid, 

 but can scarcely be said to form a precipitate; if however, 

 the experiment be reversed, i. e. if jelly be added to the in- 

 fusion after the action of the oximuriate of tin, a copious 

 precipitate is thrown down. 

 Is tan always It has been a much agitated point, whether tan be in all 

 identical? cases uniform in its properties, or whether there may not be 



substances poffefTed of the leading characteristics of tan, 

 particularly its property of precipitating jelly, which yet, in 

 some respects, may differ from each other. This latter 

 opinion has been adopted by Proust; while Mr. Davy, on the 

 contrary, appears inclined to attribute any diversity of ope-r 

 ration on the different reagents, not to any difference in the 

 ran itself, but to the peculiar substances with which it may- 

 be 



