Polytechnic Association Proceedings, 759 



external application, is easily burst open by a comparatively slight 

 force created by the enlargement of the kernel. 



4. The infusion of large blocks of limestone with moisture, by 

 the application of steam, causes them to burn and crumble with 

 one-third the amount of heat required to burn broken limestone, in 

 the usual manner of burning it. 



Is it not evident that if the swelling of the outward particles of 

 the flour in the immersed barrel, and of the lumps of flour and 

 starch formed in the boiling, causes such a close approximation of 

 their external or outward component parts as to become impervious 

 to the surrounding water, or that this imperviousness is produced 

 by the presence and resistance of air inclosed within the large and 

 the small quantities of flour and starch; or that the water is pre- 

 vented from entering in by a (combination of both causes, that we 

 can, on precisely the same grounds, account for the fact why the 

 center of each piece of ground bark retains so long such a con- 

 siderable portion of its tannin, as is exhibited by its dry, hard 

 center, on being broken? 



A due consideration of these facts, together with the remedies 

 for some of them, the comparative efiect of an external and internal 

 force or pressure on a nut shell, and the application of internal force 

 upon blocks of limestone, will enable you to estimate and under- 

 stand the causes and effect of steam upon even, unground bark 

 when in a damp state, and will account to you for its immediate 

 thorough softening, and the facility with which its tanning proper- 

 ties thus dissolved, can be removed, and for the ground and 

 unground bark being then reduced to a perfect caput mortuum, 

 almost worthless as a fuel, the burning quality of spent tan being 

 always a true criterion of the extent to which the proper leaching 

 of the bark has been completed. 



In upward leaching, the liquid as it advances upwards permeates 

 equally through every part of the leacb, whatever its shape, as 

 well as through every particle of the bark contained therein, dis- 

 placing out of each piece the inclosed air as the liquor advances 

 upwards. No formation or clogging of impenetrable dust take.s 

 place; the liquor comes off" as clear as brandy. A more perfect leach- 

 ing or spending of the bark, and in much less time, is thus eflfected. 



And I will now add, that no expense is needed to enable your 

 present leaches to be worked as upward pressed leaches, beyond 

 what would be or is needed to enable them to do the work they 

 are now intended to do, in a proper manner. 



