258 EXPERIMENTS ON ASTRINGENT VEGETABLES* 



grees with water ; the leaft quantity of precipitate being al- 

 ways produced by the leaft concentrated liquor. In all cafes,* 

 when the weak folutions were ufed, it was obferved, that the 

 refidual fluid, though palled two or three times through the 

 filtre, (till remained more or Iefs turbid and opaque ; fo that it 

 is moll likely that the deficiency arofe from the continued fuf- 

 penfion of Come of the minutely divided folid matter in the 

 liquid mafs. 

 The folutions of The folutions of gelatine, for the purpofes of analyfis, fliould 



jJJfcSi? be em P lo )' ed on, > T when q« ite f r efll > and in as high a Hate of 

 very ftrongj faturation as is compatible with their perfect fluidity. I have 

 obferved, that in cafes when they approach towards the Hate 

 of jelly, their power of a&ing upon tannin is materially altered, 

 and they produce only a very flight precipitation. As the 

 degree of fluidity of folutions of gelatine is influenced by their 

 temperature, I have found it expedient, in all comparative ex- 

 periments, to bring them and the aftringent infufionson which 

 they are defigned to act, as nearly as poffible to a common 

 at the tempera, degree of heat. My ftandard temperature 'has been between 

 tare 60*. 6a and 70° Fahrenheit; and the folutions of gelatine that I 



have ufed, were made by diflblving 120 grains of ifinglafs in 

 20 ounces of water. 

 If an excefs of In afcertaining the proportions of tannin in aftringent infu- 

 fome of the ^ &****« great care mufl be taken to prevent the prefence of any 

 tannin will be excefs of gelatine ; for, when this excefs exifts, I have found 

 redifiblved. t}iat a f ma ]j p ort i on f tne { \[^ compound formed is rediflblved, 

 and the refults of the experiment otherwife affected. It is not 

 difficult to difcover the precife point of faturation, if the folu- 

 tion of ifinglafs be added only in fmall quantities at a time, and 

 if portions of the clear liquor be palled through a filtre at dif- 

 ferent periods of the procefs, The properties of thefe portions 

 will indicate the quantities of the folution of gelatine required 

 for the completion of the experiment. 

 Thecomparifons That the compofition of any precipitate containing tannin 

 of the quantities . j ge ] at j ne may De k nown w j ln a tolerable degree of preci- 



of precipitant . . . 



and Die*ipitate fion, it js neceflary that the ifinglafs employed in the folution, 

 made after ^ anc j lne new CO mpound formed, be brought as nearly as poffi- 

 ble to the fame degree of drynefs. For this purpofe, I have 

 generally expofed them, for an equal time, upon the lower 

 plate of a fand-bath, which was feldom heated to more than 



150° 



