23 



tion of samples, previous to purchase, would be a 

 great step towards rendering his business safe, con- 

 sistent, and regularly profitable ;* and would, no 

 doubt, be the means of introducing general im- 

 provements into every branch of the manufacture. 

 " To arrive at this is the object of the present 



essay." 



* * * * 



[Here follow some pages of discussion on modes 

 of valuation formerly proposed, of more interest to 

 the scientific chemist than the manufacturer. We 



go at once to the matter of mercantile importance.] 



* * * # 



" In endeavouring to strike out an unexception- 

 able process for the use of tanners, and complete 

 this test in the spirit of utility in which Sir H. 

 Davy had first conceived it, I found it necessary to 

 take a different path from that pursued by Proust 

 and Tromsdorff, who endeavoured by the action of 

 reagents to deprive tan of the various matters na- 

 turally combined with it, and which essentially 

 modify its action in every case hitherto brought 

 under our notice. Now, the test required ought 

 to resemble in its action, that which takes place in 

 a tanner's pit ; for if the mode of trial adopted 

 differ materially in principle from the manufactu- 

 ring process which it is framed to aid, any estimate 

 of the value of astringents found on it will be se- 

 riously in error. For instance, a tanner's profit 



* A friend assures me, that valonia (which is now much in demand 

 amongst tanners at L.28 a ton) was offered to them from Italy, thirty 

 years ago, in any quantity, at L.4 a ton, but in vain ; they then had 

 no means of ascertaining its value experimentally- 



