Dr. Playfair’s Lecture on the Great Exhibition of 1851. 29 
myself with these few isolated examples, and pass on to other 
subjects. 
Leather.—The manufacture of leather has been less advanced 
by the application of Chemical Science than any other of the arts. 
If Simon, the tanner of Joppa, had been able to send leather to 
the Exhibition, no doubt he would have carried off a medal for 
leather as good, and made exactly by the same process, as that 
of ovlr most eminent manufacturers of the present day. And yet 
the science of leather production is better understood now than 
then; but so many physical conditions are involved in the pro- 
duction of good leather, that scientific processes have been unable 
to satisfy them all. The hides, steeped in an infusion of oak- 
bark, absorb tannin and are converted into leather. Good sole 
leather takes about a year to tan, and even calf-skins consume a 
month in the operation. Chemists have certainly indicated sub- 
stitutes for bark, containing a greater amount of tannin, and 
these, as for instance terra japonica, cutch, catechu, and dividivi, 
produce their effects in half the time; but the leather is said not 
to be so durable. With sumach, light skins may be tanned in 
Exosmosis have been called in to accelerate the process ; heav 
rollers have squeezed the solution through the pores; but all these 
methods have had at the best but a doubtful success. Leather- 
manufacturers meet men of science by the well-founded assertion, 
that the resulting leather is too porous, too hard or too soft, or 
not sufficiently durable ; and they revert to their old traditional 
modes of preparation. I allude to these failures the more espe- 
cially to show that there is a wide chasm between the chemist’s 
laboratory and the workshop,—a chasm which has to be bridged 
over by the united aid of the philosopher and the manufacturer, 
One without the other does not suffice, but both, working to- 
hew uses to comparatively valueless objects. In removing the 
hair from the hides, previous to tanning, it was customary to 
