80 farmers' and mechanics' journal, 



ing \vi(h the strongest, by which the process is considerably short- 

 ened. It is said, however, that the leather thus prepared, is more 

 liaoie to crack, than that manufactured in the usual method. 



It may be here remarked, that oak bark contains a number of 

 other substances, besides the astringent matter, and that, therefore, 

 the quality of the leather depends in a great measure on the mode 

 in which th*^ infusions are made. One of the substances in the 

 bark, is what is called extract, and which is soluble, but not so 

 much so as the astringent matter. Skin has the power of absorb- 

 ing this, by which the leather probably acquires its color and flexi- 

 bility ; if, therefore, the tan-liquor be so made, that it contains 

 little of the extract, the leather prepared may absorb a great deal 

 of the astringent matter, and thus become brittle, and more liable 

 to crack. Hence {)robahly the cause of that manufactured in the 

 French way not being so durable as the other, for. by the method 

 of forming the tanning iluid, much of the astringent, and little of 

 the extractive matter is dissolved. Besides, when the process is 

 carried on quickly, the outer part of the skin only is converted 

 into leather, because, this being speedily tanned, prevents the fluid 

 from penetrating any farther. 



The great objects to be attended to, then, in tanning, are, to pro- 

 cure from the bark as much of the soluble matter as possible, and, 

 could some means be devised by which the skins could be made to 

 imbibe this quickly, a great deal of labor, time, and money, would 

 be saved. On this is founded the patent process of Spilsbury, of 

 forcing in the tan-liquor by pressure. For this purpose the skins, 

 after being cleaned, are stretched on frames, which apply closely 

 to each other, but so as to leave a little space between the hides. 

 Pipes are connected with these, and the fluid allowed to flow into 

 the compartments from a cistern placed above them, by which, 

 owing to the pressure, it is forced into the hides. It is said, that 

 in this way, skins which require a year according to the old mode, 

 may be tanned in six weeks, and that some may be finished in a 

 few days ; it is doubtful, however, if the leather prepared is so du- 

 rable, for, from the forcing in of the fluid, the skin does not appear 

 to take it in uniformly, so as to tan completely the whole of it. 



The tawing of skins, by which they are also converted into 

 leather, is more speedily accomplished than tanning. The skins 

 subieeted to this process, are those of goats, sheep, lambs, and other 

 thin hides, by which glove leather, and that usually called morocco, 

 are prepared. When the leather is to be white, it is merely sub- 

 jected to tawing, but when intended to be dyed, it also receives a 

 slight tanning. 



The process followed for preparing the skins, is nearly the same 

 as that described. They are first freed of the dirt and blood by 

 washing, and hung in a room heated by stoves, till they begin to 

 putrefy, which is known by their emitting the odour of ammonia 

 or hartshorn. During this a slimy matter collects on the surface, 

 which is removed by placing them on a cylindrical piece of wood, 

 and scraping them with a knife, and the hair is at the same time 



