CHAPTER 6.

Saving time in Natural Operations

47. The process of tanning will furnish us with a striking
illustration of the power of machinery in accelerating certain
processes in which natural operations have a principal effect.
The object of this art is to combine a certain principle called
tanning with every particle of the skin to be tanned. This, in
the ordinary process, is accomplished by allowing the skins to
soak in pits containing a solution of tanning matter: they remain
in the pits six, twelve, or eighteen months; and in some
instances (if the hides are very thick), they are exposed to the
operation for two years, or even during a longer period. This
length of time is apparently required in order to allow the
tanning matter to penetrate into the interior of a thick hide.
The improved process consists in placing the hides with the
solution of tan in close vessels, and then exhausting the air.
The effect is to withdraw any air which may be contained in the
pores of the hides, and to aid capillary attraction by the
pressure of the atmosphere in forcing the tan into the interior
of the skins. The effect of the additional force thus brought
into action can be equal only to one atmosphere, but a further
improvement has been made: the vessel containing the hides is,
after exhaustion, filled up with a solution of tan; a small
additional quantity is then injected with a forcing-pump. By
these means any degree of pressure may be given which the
containing vessel is capable of supporting; and it has been found
that, by employing such a method, the thickest hides may be
tanned in six weeks or two months.

48. The same process of injection might be applied to
impregnate timber with tar, or any other substance capable of
preserving it from decay, and if it were not too expensive, the
deal floors of houses might thus be impregnated with alumine or
other substances, which would render them much less liable to be
accidentally set on fire. In some cases it might be useful to
impregnate woods with resins, varnish, or oil; and wood saturated
with oil might, in some instances, be usefully employed in
machinery for giving a constant, but very minute supply of that
fluid to iron or steel, against which it is worked. Some idea of
the quantity of matter which can be injected into wood by great
pressure, may be formed, from considering the fact stated by Mr
Scoresby, respecting an accident which occurred to a boat of one
of our whaling-ships. The harpoon having been struck into the
fish, the whale in this instance, dived directly down, and
carried the boat along with him. On returning to the surface the
animal was killed, but the boat, instead of rising, was found
suspended beneath the whale by the rope of the harpoon; and on
drawing it up, every part of the wood was found to be so
completely saturated with water as to sink immediately to the
bottom.

49. The operation of bleaching linen in the open air is one
for which considerable time is necessary; and although it does
not require much labour, yet, from the risk of damage and of
robbery from long /exposure, a mode of shortening the process was
highly desirable. The method now practised, although not
mechanical, is such a remarkable instance of the application of
science to the practical purposes of manufactures, that in
mentioning the advantages derived from shortening natural
operations, it would have been scarcely pardonable to have
omitted all allusion to the beautiful application of chlorine, in
combination with lime, to the art of bleaching.

50. Another instance more strictly mechanical occurs in some
countries where fuel is expensive, and the heat of the sun is not
sufficient to evaporate the water from brine springs. The water
is first pumped up to a reservoir, and then allowed to fall in
small streams through faggots. Thus it becomes divided; and,
presenting a large surface, evaporation is facilitated, and the.
brine which is collected in the vessels below the faggots is
stronger than that which was pumped up. After thus getting rid of
a large part of the water, the remaining portion is driven off by
boiling. The success of this process depends on the condition of
the atmosphere with respect to moisture. If the air, at the time
the brine falls through the faggots, holds in solution as much
moisture as it can contain in an invisible state, no more can be
absorbed from the salt water, and the labour expended in pumping
is entirely wasted. The state of the air, as to dryness, is
therefore an important consideration in fixing the time when this
operation is to be performed; and an attentive examination of its
state, by means of the hygrometer, might be productive of some
economy of labour.

51. In some countries, where wood is scarce, the evaporation
of salt water is carried on by a large collection of ropes which
are stretched perpendicularly. In passing down the ropes, the
water deposits the sulphate of lime which it held in solution,
and gradually incrusts them, so that in the course of twenty
years, when they are nearly rotten, they are still sustained by
the surrounding incrustation, thus presenting the appearance of a
vast collection of small columns.

52. Amongst natural operations perpetually altering the
surface of our globe, there are some which it would be
advantageous to accelerate. The wearing down of the rocks which
impede the rapids of navigable rivers, is one of this class. A
very beautiful process for accomplishing this object has been
employed in America. A boat is placed at the bottom of the rapid,
and kept in its position by a long rope which is firmly fixed on
the bank of the river near the top. An axis, having a wheel
similar to the paddle-wheel of a steamboat fixed at each end of
it, is placed across the boat; so that the two wheels and their
connecting axis shall revolve rapidly, being driven by the force
of the passing current. Let us now imagine several beams of wood
shod with pointed iron fixed at the ends of strong levers,
projecting beyond the bow of the boat, as in the annexed
representation.

If these levers are at liberty to move up and down, and if
one or more projecting pieces, called cams, are fixed on the axis
opposite to the end of each lever, the action of the stream upon
the wheels will keep up a perpetual succession of blows. The
sharp-pointed shoe striking upon the rock at the bottom, will
continually detach small pieces, which the stream will
immediately carry off. Thus, by the mere action of the river
itself, a constant and most effectual system of pounding the rock
at its bottom is established. A single workman may, by the aid of
a rudder, direct the boat to any required part of the stream; and
when it is necessary to move up the rapid, as the channel is cut,
he can easily cause the boat to advance by means of a capstan.

53. When the object of the machinery just described has been
accomplished, and the channel is sufficiently deep, a slight
alteration converts the apparatus to another purpose almost
equally advantageous. The stampers and the projecting pieces on
the axis are removed, and a barrel of wood or metal, surrounding
part of the axis, and capable, at pleasure, of being connected
with, or disconnected from the axis itself, is substituted. The
rope which hitherto fastened the boat, is now fixed to this
barrel; and if the barrel is loose upon the axis, the
paddle-wheel makes the axis only revolve, and the boat remains in
its place: but the moment the axis is attached to its surrounding
barrel, this begins to turn, and winding up the rope, the boat is
gradually drawn up against the stream; and may be employed as a
kind of tug-boat for vessels which have occasion to ascend the
rapid. When the tug-boat reaches the summit the barrel is
released from the axis, and friction being applied to moderate
its velocity, the boat is allowed to descend.

54. Clocks occupy a very high place amongst instruments by
means of which human time is economized: and their multiplication
in conspicuous places in large towns is attended with many
advantages. Their position, nevertheless, in London, is often
very ill chosen; and the usual place, halfway up on a high
steeple, in the midst of narrow streets, in a crowded city, is
very unfavourable, unless the church happen to stand out from the
houses which form the street. The most eligible situation for a
clock is, that it should project considerably into the street at
some elevation, with a dial-plate on each side, like that which
belonged to the old church of St Dunstan, in Fleet Street, so
that passengers in both directions would have their attention
directed to the hour.

55. A similar remark applies, with much greater force, to the
present defective mode of informing the public of the position of
the receiving houses for the twopenny and general post. In the
lowest corner of the window of some attractive shop is found a
small slit, with a brass plate indicating its important office so
obscurely that it seems to be an object rather to prevent its
being conspicuous. No striking sign assists the anxious enquirer,
who, as the moments rapidly pass which precede the hour of
closing, torments the passenger with his enquiries for the
nearest post-office. He reaches it, perhaps, just as it is
closed; and must then either hasten to a distant part of the town
in order to procure the admission of his letters or give up the
idea of forwarding them by that post; and thus, if they are
foreign letters, he may lose, perhaps, a week or a fortnight by
waiting for the next packet.

The inconvenience in this and in some other cases, is of
perpetual and everyday occurrence; and though, in the greater
part of the individual cases, it may be of trifling moment, the
sum of all these produces an amount, which it is always worthy of
the government of a large and active population to attend to. The
remedy is simple and obvious: it would only be necessary, at each
letter-box, to have a light frame of iron projecting from the
house over the pavement, and carrying the letters G. P., or T.
P., or any other distinctive sign. All private signs are at
present very properly prohibited from projecting into the street:
the passenger, therefore, would at once know where to direct his
attention, in order to discover a post-office; and those
letter-boxes which occurred in the great thoroughfares could not
fail to be generally known.