That is, in 1 chloride of lime and carbonic acid react upon each other,
producing chalk and nascent chlorine; in 2 the nascent chlorine reacts
upon the water of the solution and decomposes it, producing hydrochloric
acid and nascent oxygen, which bleaches; in 3 the hydrochloric acid just
formed reacts upon chalk formed in 1, and produces calcium chloride and
one equivalent of water, and at the same time frees the carbonic acid to
be used again in the process of decomposing the chloride of lime.
When the process was first brought to the notice of the Lancashire
bleachers, it met with an amount of opposition. Some bleaching chemists
declared the process was not patentable, as fully half a century ago
carbonic acid was known to decompose chloride of lime. The patentee's
answer was emphatic, that carbonic acid gas had never been applied in
bleaching before. After some delay one of the largest English cotton
bleachers, Messrs. Ainsworth, Son & Co., Halliwell, Bolton, threw open
their works for a fair test of the Thompson process on a commercial
scale.
The result of trial was so satisfactory that a company was formed to work
the patent. Soon after this the well-known authorities on the oxidation
of cellulose, Messrs. Cross & Bevan and Mr. Mather, the principal partner
in the engineering firm of Mather & Platt, of Salford, Lancashire, joined
the company. For the last twelve months these gentlemen have devoted
considerable attention to improving the original contrivance of Thompson,
and a few weeks since they handed over to Messrs. Ainsworth the machinery
and instructions for what they considered the most complete and best
process of bleaching that has ever been introduced.
Recently a "demonstration" of the "Mather-Thompson" process of bleaching
took place at Halliwell, and to which were invited numerous chemists and
practical bleachers. Having been favored with an invitation, I propose to
lay before your readers a concise report of the proceedings.
It is usual in this country to give a short preliminary boil to the cloth
before it is brought in contact with the alkali, the object being to well
scour the cloth from the loose impurities present in the raw fiber and
also the added sizing materials. In the new process the waste or spent
alkaline liquors of the succeeding process are employed, with the result
that the bleaching proper is much facilitated. The economy effected by
this change is considerable, but in the next operation, that of
saponification, the new process differs even more widely from those
generally in use. In England, "market" or "white" bleaching requires a
number of operations. There is first the alkaline treatment divided into
the two stages or processes of lime stewing and bowking in soda-ash,
which only imperfectly breaks down the motes. There is consequently a
second round given to the goods, consisting of a bowk in soda-ash,
followed by the second and usually final chemicking. There is, therefore,
much handling of the cloth, with the consequent increase of time and
therefore expense.
Now, in the saponification process, the Mather-Thompson Company claim to
have achieved a complete triumph. They use a "steamer keir," the
invention of Mr. Mather. This keir is so constructed that it will allow
of two wire wagons being run in and the door securely fastened. At the
top of the keir is fixed a mechanical appliance for steaming the cloth.
The steamer keir process consists essentially in:
1. The application of the alkali in solution and in its most effective
form, viz., as caustic alkali, to each portion of fiber in such quantity
as to produce the complete result upon that portion.
2. The immediate and sustained action of heat in the most effective form
of steam.
Before the cloth is run into the steamer keir on the wire wagons, it is
saturated with about twice its weight of a dilute solution of caustic
soda (2° to 4° Twaddell = 0.5 to 1% Na_{2}O) at a boiling-temperature,
when in the steamer keir it is exposed to an atmosphere of steam at four
pounds pressure for five hours. This part of the process is entirely new.
The advantage of using caustic soda alone in the one operation, such as I
describe, has been long recognized, but hitherto no one has been able to
effect this improvement. It will be observed that the Mather-Thompson
process does away entirely with the use of lime and soda-ash in at least
two boilings and the accessory souring operation. In the space of the
five hours necessary for the steamer keir process the goods are
thoroughly bottomed and all the motes removed, no matter what be the
texture or weight of the cloth. After the cloth is washed in hot water it
is removed from the steamer keir, then follows a rinse in cold water, and
the goods are ready for the bleaching process.
In passing to the bleaching and whitening process, it may be necessary to
say that thus far the original Thompson process has been entirely
altered. Now we come to that part of the bleaching operation where the
essential feature in Thompson's patent is utilized. The patentee has
apparently thoroughly grasped the fact that carbonic acid has great
affinity for lime and that it liberates, in its gaseous condition, the
hypochlorous acid, which bleaches. The most perfect contact is realized
between the _nascent_ hypochlorous acid resulting from its action and the
fiber constituent in the exposure of the cloth treated with the bleaching
solution to the action of the gas. The order of treatment is as follows:
(1) Saturation with weak chemic (1° Tw.), squeeze,
and passage to gas chamber.
(2) Wash (running).
(3) Soda scald.
(4) Wash.
(5) Repetition of 1, but with weaker chemic (½° Tw.).
(6) Wash.
(7) Scouring.
The whole of the above operations are carried out on a continuous plan,
the machinery being the invention of Mr. Mather. The cloth travels along
at the rate of sixty or eighty yards a minute, and comes out a splendid
white bleach. The company consider, however, that it is necessary in the
case of some cloth to give a second treatment with chemic and gas, each
of thirty seconds duration, with an intermediate scald in a boiling very
dilute alkaline solution. Mr. Thompson originally claimed that the use of
carbonic acid gas rendered the employment of a mineral acid for souring
unnecessary. It is considered now to be advisable to employ it, and the
souring is included, as will be observed, in the continuous operation.
The new process for treating cloth differs materially from that
originally proposed by Mr. Thompson. His plan was to use an air-tight
keir in conjunction with a gas-holder. It is obvious that the
"continuous" process would not answer for yarns; Thompson's keir is,
therefore, employed for these and all heavy piece-goods.
Thus far I have given a concise outline of the Mather-Thompson process of
bleaching, which, it cannot be denied, differs materially from any system
hitherto recommended to the trade. Beyond doubt the goods are as
perfectly bleached by this process as by any now in use. The question
arises, What pecuniary advantage does it offer? Mr. Manby, the manager of
Messrs. Ainsworth, has informed me that he has bleached as much as ten
miles of cloth by the new process, and is, therefore, entitled to be
heard on the subject of cost. In regard to the consumption of chemicals,
he estimates the saving to amount to (in money value) one-fourth; steam
(coal), one-half; labor, one-half; water, four-fifths; time, two-thirds.
It might be well to contrast the process formerly employed by Messrs.
Ainsworth with that they have recently adopted:
"MATHER-THOMPSON" SYSTEM.
Alkali. Bleach Acid Machine
(chemic). Washes.
/ Saturate.
(1) <
\ Steam.
/ (2) Continuous
| (chemic)
| machine
| (or keir if
(2) < for yarns,
| etc.).
| (2a) Machine or
\ pit sour.
(3) Wash up for
finishing.