1825.] comparative Tanning Powers of^ Astringents, 46^' 



In Birmingham (I am informed) this branch of the leather 

 manufacture is well understood. In DubHn we have but one 

 splitting machine, and that is only constructed for splitting 

 sneep skins. These, from the improvement which has taken 

 place in our breed of sheep, are generally so full of fat, that 

 they are quite unfit to act as a test in this case, the oil shielding 

 the skin from the action of the tan, and where it exists in 

 greatest quantity along the back and across the neck, retarding 

 the evaporation of moisture during the two drying processes, 

 and consequently leading to false results. 



Calfskins^ shaven down to the thinness of split sheep skins;'' 

 are free enough from oil, but the fibre is in general so delicate, 

 that it is liable to be injured, and partially dissolved, or rather 

 dispersed through the warm water during the softening and swell- 

 ing, preparatory to steeping in the astringent infusion. I found 

 that several lots of this skin, previously dried and weighed for 

 experiment, though beautifully transparent, and apparently 

 perfect in every way, lost seven per cent, of loose gelatine when 

 handled in tepid water. Thus this species of skin also appears 

 improper for the purpose. 



To avoid the last mentioned source of error, it will be prudent 

 to reserve a piece out of every batch which undergoes the 

 swelling process, to ascertain (by drying and weighing without 

 tanning) whether the remaining pieces destined for experiment 

 had lost any thing in that operation. As such a loss is only 

 likely to occur in strong hides from carelessness in the usual 

 operations of lining, washing, &c. the tanner has it completely 

 in his power, by proper attention, to prepare his own test skins 

 in the most perfect manner. Perhaps the calf skins that I 

 operated on had been somewhat injured in these previous pro- 

 cesses ; whereas if they had been carefully treated, they might 

 have remained strong enough. This is a point which peculiarly 

 rests with the tanner to ascertain correctly, as a matter of 

 economy and convenience. If calf skins be really strong enough 

 to retain all their substance from one weighing to the other, 

 tanners who manufacture upper leather will be much more at 

 home in trials made with them. In Ireland, I believe, there is 

 quite as much of it made as of sole leather. 



In the shaving of strong hides, it is indifferent to the currier 

 in what shape he takes off the pieces. A tanner who attends 

 him during that operation may obtain shavings of the exact size 

 he wants, and, therefore, need never sacrifice an entire hide to 

 the experiment. 



I need scarcely mention that the test skins employed in this 

 trial should not be expected to become perfect leather, so as to 

 enable the tanner to judge of the quality of the astringent also. 

 That is an operation requiring length of time, and excess of 

 tanning materials, both of which are here inadmissible. 



