Vermont telegraph. [volume] (Brandon [Vt.]) 1828-1843, 1841-08-04

SiuE duu III du lHHuhtSiJ otho1A uiSeohSS
within, there is a perfect combination Of
Tannin with the Gelatine, and upon press
ing the piece with the hand, water, pure
and transparent will ooze from it in consid-
cradle quantities. II
The difficulty of extracting or expelling
this water in order that the space il occupies
might be filed with new, portions Of liquor
charged with Tannin, has hitherto been an
obstacle to the production Of a complete and
speedy tan, which no means or appliances
have ever removed. Attempts have been
made to expel it by the mechanical action
of powerful presses and rollers. Heat has
been applied in order to increase the tinidity
| of the liquor, and the permeability of the +
skins by expanding their pores, thus afford |
ing to the liquor freer ingress and egress.
J Beth methods however have resulted as be- |
fore intimated, in some injury TO the leather.
Toward the displacement of this uncharg-
ed water and Gallo acid, Mr.. How'd directed |
his researches and has discovered, ii is be- |
lieved, process fully accomplishing the
object, well founded in theory and well sus-
tanned by actual experiment. He construct
ed cylindrical vat, air tight, with pipe
for the, purpose Of filing it, inserted at the
upper side and leading TO reservoir below;
the pipe being closed by cock near the
, inserted end. At the lower side another
cock is inserted as discharger. On the
upper side is fitted small vent cock for the
admission Of air at the time Of discharging.
On the upper side is an orfce or rnan-hole
with a stop-plate at which the skins are put
in and taken out. And at one end on the
upper side, an air pump is adapted, with
cock below the lower valve, for the purpose
Of exhausting the air from within the vat.
Having thus arranged his apparatus he
suspended within the vat some skins, pre-
pared in the ordinary way, shut down the
stop-plate, closed the proper cocks, and
worked the pump until he produced as near
as possible vacuum. This partial vacuum
was kept up one hour, when the cold hem
lock liquor from the cellar below was ad-
mitted into the vat and suffered 10 remain
10 minutes. 1t was then discharged and
the vat exhausted Of air and kept so for
another hour. The liquor was again ap-
piled and suffered to remain other 10 min
utes, and thus repeated alternately until the
liquor had been applied to the skin 6 times
, 10 minutes each; when a piece of calf skin
Of ordinary thickness was taken out, dri
and curried, and by good judges was pro-
! nounced to be first and unequaled quality
of leather. Other experiments were tried
by which thicker and heavier pieces of skins
! were tanned by the same process, having the
E liquor applied to them from IL to Is times
r of 10 minutes each, and when curred were
declared by experienced Shoemakers and
Tanners to be handsomer, stronger and more
flexible leather than if tanned By the old,
slow process. By the first experiment the
!. whole time occupied in tanning piece OF
leather was only IL hours, and by the 9TH
; , els, only "a and Sc hours.
The theory of the process thus shown to
: be so completely sustained by experiment
!. is as follows The exhausting of the air
i from the vat removes from the skins that
q atmospheric pressure which is prominent
\ component principle of capillary attraction,
. consequently greatly diminishing the force
;, Of this attraction, which when encounter
r. acted retain the unchanged liquid, and pre-
q vents its dripping from the pores Of the sus-
;. pended skins. The exhaustion causes a
. rapid evaporation, the results of which is to
= throw off in the form of vapoF, large pro-
= portion of the unchanged water and Gallo
! acid remaining in, and upon the skins; for
liquids assume the aeriform state very rap
? idly under diminished pressure, especially
. if the vapor which is formed be drawn off
e as soon as il is produced, so as TO maintain
:. the vacuum as in the case of these expert
ments. The rapid evaporation caused by
the vacuum, produces very considerable
reduction of temperature within the vat, the
: effect of which is 10 contract the fibre of
. the skins, thereby expelling by their con-
: traction much Of the unchanged water that
a may be remaining within and upon the skins.
), The removal Of the air from the surface OF
> the skins causes an expansion Of the air
i within, to such degree that much Of it
i escapes and is replaced by the liquor when
e admitted; and during lis escape it removes
: IAN particles of unchanged liquid that in any
d way impedes itsprogress towards the surface.
r The vacuum when produced over the liquor
e in the vat nearly full, creates an ebulition