406 i. >- vvv > I.. Mr, Stephens on the [Dsci 



of the varitwsr rtatt^ra naturally 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 

 manufacturing process which it is framed to aid, any estimate 

 of the value of astringents founded on it will be seriously in 

 error. For instance, a tanner's profit chiefly depends on the 

 increase of weight which a hide acquires during the process that 

 converts it into leather. This in strong (sole) leather is generally 

 one-third of the dry weight, or, what tanners are more accus- 

 tomed to calculate on in Ireland, the finished leather is half the 

 weight of the hide when fresh from the slaughter-house. The 

 extractive matter forms an important part of this weight, and, 

 therefore, any test which the manufacturer might apply to ascer-» 

 tain the tanning power of an astringent material, and which acted 

 only on pure tan, would completely mislead him. I am inclined 

 to think any gallic acid present is also absorbed by the skin. In 

 spent ouze the power of striking black precipitates with solutions 

 of iron is lost, and transferred to the leather, particularly that 

 made with oak bark. In short the tanner wants something which, 

 when presented to an astringent infusion, will seize on, and 

 enable him to estimate every thing which would (in his process 

 on the large scale) contribute to the weight of his leather. 



I know nothing which can do this so well as the skin itself, 

 and I find that by a little management it may be made to yield 

 us the information we require, quicker than has hitherto been 

 thought possible. 



It cannot be doubted that a strong bull hide will continue to 

 absorb tanning matter for two years, if the process be so 

 arranged ; but if we alter the usual proportion of the materials, 

 the result, as to time, will difi'er exceedingly. If a fresh skin be 

 shaven down to a very thin substance on a currier's beam, or 

 split into fine leaves by a machine, so as to expose a great 

 expanse of surface, and a quantity of these be steeped in a pro- 

 portionally small measure of tanner's ouze, they will in a very 

 very few hours imbibe all its useful tanning substance, and 

 enable him to ascertain, by the difference of weight before and 

 after steeping, the exact quantity of matter in solution, that can 

 be made available in the manufacture of leather.* 



This is a test which comes home to the business of every 

 tanner ; one which he can place confidence in, because he can 

 clearly understand it; and thoughisome niceties are requisite in 

 this process also, the line of thought necessary to attain them 



* The strongest ouze in a Dublin tan yard, prepare4 in the usual cold method, was 

 exhausted of taste and colour by this mode in seven hours ; a decoction of valonia (the 

 strongest I was able to make) of sp. gr. 1065, was, with the aid of frequent manipulation, 

 to change the ouze in the pores (rfthe skin, deprived of all astringency in about nine hours* 



