In the tanning (^Leather. 319 
circumference of eight feet ; yet it has been found that this sin- 
gular rapidity of growth by no means diminishes the density 
and durability of the timber, which has been already found to 
be equally adapted to the purposes of naval and domestic archi- 
tecture. Granting that, for shipbuilding, this larch were in- 
ferior to the oak, this affords no solid objection to its use as a 
valuable addition to the resources of the State, as it attains per- 
fection in one half of the period required for the oak attaining 
its full value. There is, however, reason to conclude, that the 
larch has been of late prematurely cut down. 
The bark of the oak had hitherto been used almost exclusive- 
ly in the process of tanning leather; but its daily increasing scarcity 
and consequent high price, arising from the great demand during 
the late war with the French, naturally led to the use of the 
barks of other trees, as substitutes for it. It was common to 
mix these last with oak bark, but in this way the result could 
never be accurately ascertained. It was necessary, therefore, to 
institute comparative experiments of the larch bark with the oak 
bark separately ; and these, to avoid the ambiguity of trials on 
a small scale, were conducted by an eminent tanner, Mr P. 
Martin of Haddington. 
(1.) Equal weights of skin were taken, as accurately as possible, 
from the same parts of the animal, and immersed, under the same 
temperature, that of the atmosphere in summer, in separate cold 
infusions of the same weight of the bark of the oak and larch, 
previously ground in the ordinary way, and treated in the same 
manner. Both sorts of leather were then dried : The same 
bulk of larch-tanned leather was found to be specifically heavier 
than that of the oak, but the proportional excess was not ac- 
curately ascertained. 
(2.) In colour, the specimens sent to me, differed remarkably; 
the larch-tanned leather being of a light fawn, whilst that 
tanned by the oak bark was of a deep brown colour. 
(3.) The larch-tanned leather absorbed water more readily than 
that of the oak, in these specimens. Circumstances of an 
accidental nature, however, sometimes regulate this property ; 
such as more or less compression, by hammering, previous to 
the operations of the shoemaker; and it is well known that slow 
