const'diient Parts of astringent Vegetables. 67 



matter from solutions, without acting materially upon gallic 

 acid ; and, after this precipitation, some idea may be tbrmed 

 concerning the quantity of the gallic acid by the colour it 

 s;ives with the oxygenated sulphate of iron. In this pro- 

 cess, however, great care must be taken not to add the so- 

 lution of the sulphate of iron in excess; for in this case 

 the black precipitate formed with the gallic acid will be re- 

 dissolved, and a clear olive-coloured fluid only w ill be ob- 

 tained. 



The saline matters in astringent infusions adhere so 

 strongly to the vegetable principles, that it is impossible 

 to ascertain their nature, with any degree of accuracy, by 

 means of common reagents. By incineration of the pro- 

 ducts obtained from the evaporation of astringent infusions, 

 I have usually procured carbonate of lime and carbonate of 

 potash. 



In the different analyses, as will be seen from the results 

 given in the following sections, I have attended chiefly to 

 the proportions of the tanning principle, and of the prin- 

 ciples precipitable by the salts of iron, as being most con- 

 nected with practical applications. 



With regard to the knowledge of the nature of the dif- 

 ferent substances, as they exist in the primitive astringent 

 infusion, we can gain, by our artificial methods of exa- 

 mination, only very imperfect approximations. In acting; 

 upon them by reagents we probably^ in niaay cases, alter 

 their nature ; and very few of them Only can be obtained in 

 an uncombined states The comparison, howciver, of the 

 products of different experiments with each other is always 

 connected with some useful conclusions ; and the accumu- 

 lation of facts with regard to the subject must finally tend 

 to elucidate this obscure but most Interesting part of che- 

 mistry. 



II. Experiments on the Infusions of Galls. 



I have been verv much assisted, in my mquirics concern- 

 ing the properties'of the infusions of galls, by the able me- 

 moir of M. Dcyeux on Galls*. 



The stron<jcst infusion of galls that T could obtain at 56" 

 Fahrenheit, by repeatedly pouring distilled water upon the 

 best Aleppo galls broken' into small pieces, and suffering it 

 to remain in contact with them till the saturation was com- 

 plete, was of the specific gravity 1-068. Four hundred 

 grains of it produced, by evaporation at a temperature be- 



'* ^"'"''t" flc Cbimir, ome xvii. p. «• 



K 9, 5ov/ 



