402 Mr, Stephens on the [Dec, 



the means of introducing general improvements into every 

 branch of the manufacture. 



To arrive at this is the object of the present essay. However, 

 as several chemists of unquestionec talent and extensive know- 

 ledge have preceded me in this inquiry, and as a prpcess to 

 effect this particular object has already been proposed by high 

 authority, it may be proper to state the circumst?inces which 

 rendered a rejection of tne mode so recommended^' ^a matter of 

 expediency, indeed of necessity. j", , 



In the year 1803, Sir H. Davy published an essay in the 

 Phil. Trans. *' On Vegetable Astringents;" and another in the 

 .Tournals of the Royal Institution, " On the Process of Tan- 

 ning," which were both of high importance to the practical 

 tanner, as affording him a clear and masterly explanation of 

 the varieties of chemical action that take place in this interesting 

 manufacture. These valuable essays peculiarly exemplify the 

 happy tact by which the talented author can so well illustrate, by 

 j)t'actical application, the importance of his scientific researches. 



In this excellent spirit of useful illustration, Sir H. Davy pro- 

 poses the following process (vide Jour. Roy. Inst. 1803) for the 

 attainment of this wished-for mercantile comparison. 



" The solution of gelatine, most proper for the general purpose 

 of experiments, is made by dissolving an ounce of glue or 

 of isinglass in three pints of boiling water. 



" The substance to be examined as to its tanning power may 

 be used in the quantity of two ounces. It should be in a state 

 of coarse powder, or of small fragments. A quart of boiling 

 water will be sufficient to dissolve its astringent principles. 



" The solution of glue, or gelatine, must be poured into the 

 astringent infusion, till the effect of precipitation is at an end. 



** The turbid liquors must then be passed through a piece of 

 blotting paper, which has been before weighed. 



<* When the precipitate has been collected, and the paper 

 dried, the increase of its weight is determined, and about 

 two-fifths of this increase of weight may be taken as the quan- 

 tity of tannin in the ounce of the substance examined." 



If no well-grounded objections had been discovered to this 

 apparently simple process, it would have ensured greater advan- 

 tages to the leather manufacture than any previously obtained 

 through the medium of scientific investigation; but Sir H. Davy 

 has, with his usual candour, stated several niceties connected with 

 its management (Phil. Trans. 1803), which, to ensure accuracy, 

 require particular attention ; and therefore tending (in the hands 

 of any but a practised experimentalist) to render the process 

 very fallacious. 



troni my own experience, I can state that the idea of this 

 nicety of manipulation, requisite by the author's own showing, has 

 been quite sufficient to deter every person in the tanning busi- 



