VOL. LXVIII.]] PHILOSOPHICAL TRANSACTIONS. 305 



and 2dly, to render it impervious to water. An infusion of any strongly astrin- 

 gent vegetable will serve to tan leather, so far as to prevent its rotting; but if 

 this vegetable does not contain a good deal of gum-resin, it will not answer for 

 enabling it to keep out water: and hence it is that oak-bark, which is more 

 abundant in the gummy resinous part than any of our common indigenous 

 astringents, is preferred to all other substances for the purpose of tanning. The 

 tanners prepare their bark by gently drying it on a kiln, and grinding it into a 

 very coarse powder. They then either use it in the way of infusion, which is 

 called ooze, or they strew the dry powder between the layers of hides and skins, 

 when these are laid away in the tan-pits. The ooze is made by macerating the 

 bark in common water, in a particular set of holes or pits, which, to distinguish 

 them from the other holes in the tan-yard, are termed letches. 



The first operation of the tanner is to cleanse the hides from all extraneous filth, 

 and remove any remains of flesh or fat which may have been left behind by the 

 butcher. The hair is next taken off; and this is accomplished either by steeping 

 the hides for a short time in a mixture of lime and water, which is termed liming, 

 or by rolling them up close, and piling them in heaps, where they quickly begin 

 to heat and putrefy. The hair being loosened is scraped off, and the tanner 

 proceeds to the operation called fleshing, which consists in a further scraping, 

 with a particular kind of knife contrived for the purpose, and cutting away the 

 jagged extremities and ofi'al parts, such as the ears and nostrils. The raw leather 

 is then put into an alkaline ley, in order to discharge the oil, and render its pores 

 more capable of imbibing the ooze. The tanners of this country (Ireland) gene- 

 rally make their ley of pigeon's dung; but a more active one may be prepared 

 from kelp or pot-ash, taking care however not to make it too strong of the ashes, 

 nor to allow the leather to remain too long in the ley. 



The oil being sufficiently discharged, the leather is ready for the ooze, and at 

 first is thrown into smaller holes, which are termed handlers; because the hides 

 or skins, during this part of the process, are taken up, from time to time, and 

 allowed to drain; they continue to work the leather in these handlers, every now 

 and then stirring it up with the utensil called a plunger, which is nothing more 

 than a pole with a knob at its end, till they think proper to lay it away in the 

 vats. In these holes, which are the largest in the tan-yard, the leather is spread 

 out smooth, whereas they toss it into the handlers at random, and between each 

 layer of leather they sprinkle on some powdered bark, till the pit is filled by 

 the leather and bark thus laid in stratum super stratum : ooze is then poured on 

 to fill up interstices; and the whole crowned with a sprinkling of bark, which 

 the tanners call a heading. In this manner the leather is allowed to macerate, 

 till the tanner sees that it is completely penetrated by the ooze: when this is ac- 

 complished (which he knows by cutting out a bit of the thickest part of the 



VOL. XIV. R R 



