£08 ON VEGETABLE ASTRINGENTS. 



by exposure to the atmosphere, and it is also removed by 

 boiling, although in this latter case it is partly reproduced 

 after an interval of two or three days, but finally disappears. 

 There seems to be an analogy between these changes, and 

 the effect of acids and alkalis on many other vegetable sub- 

 stances, they are rendered green by an alkali, and are red- 

 dened by an acid. But the resemblance does not hold good 

 in every respect; for the alkaline mixture loses its green co- 

 lour, although its alkalescent properties continue; and I 

 have observed the green colour to be removed by lime and 

 ammonia, while, on the contrary, I have obtained infusions* 

 which have exhibited the green colour, and yet by the test 

 of litmus have proved to be decidedly acid.. The green co- 

 lour, wherever it exists, is immediately destroyed by the 

 in infusion of acetate of lead*. With respect to the existence of lime in 

 galls, the infusion of galls, the experiments which I have made on 



the subject lead me to conclude, that, although it may exist 

 in the gall-nut, yet it is not taken up by the water. 1 have 

 added to the recent infusion of galls both uncombined oxalic 

 acid, and the oxalate of ammonia, without any precipitate 

 being produced. If the ammonia be in excess a consider- 

 able effect takes place, but this is to be ascribed to the union 

 of the uncombined alkali with the tan. 



If the infusion of galls be kept for any length of time, it 

 always becomes covered with mould, and a sediment also 

 falls to the bottom of the vessel. The moulding has been 

 attributed by Deyeux, Trommsdorff, and others, to the pre- 

 sence of mucus, as mucus is said to be the only substance, 

 which is capable of supporting this species of vegetation f. 

 I conceive, however, that this opinion is not correct ; and 

 % that, even if there be any thing in the infusion, to which the 



name of mucus properly applies, it is not the immediate 

 cause of the formation of the mould. The muriate of tin, 

 and the solution of jelly are the two principal reagents, 



* I employ the term acetate of lead in the restricted sense, in which 

 it is used in the new Pharmacopoeia of the London College, where I may 

 remark, the distinction which I pointed out between Goulard and ce- 

 russaacetata is recognized, and the appropriate nomenclature adopted. 

 Powel's Translation of the New Pimm; p. 157. 



t Ann. de Chem. XVII, 15 ; and Thomson's Chem. II, 356. 



which 



