In the spring of 1883 a Mr. J.B. Thompson, of New Cross, London, patented a new process of bleaching, the main feature of which consisted in the use of carbonic acid gas in a closed vessel to decompose the chloride of lime. The "chemicking" and "souring" operations he performed at one and the same time. The reactions which took place in his bleaching keir were stated by the inventor as follows:
Cl.\ 1. Ca ) + CO₂ = CaCO₃ + Cl₂. OCl./ 2. OH₂ + Cl₂ = (ClH)₂ + O. 3. CaCO₃ + (ClH)₂ = CaCl₂ + CO₂ + H₂O.
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% NaO) 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. ORDINARY SYSTEM. Alkali. Bleach. Acid Machine Washes. (1) Lime stew. (1) Wash. (2) Sour. (2) " (3) Gray bowk (3) " (soda ash). (4)I Chemic. (4) " (5) Sour. (5) " (6) White bowk. (6) " (7)II Chemic. (7) " (8) Sour. (8) "
It will be understood that 2 and 2a are merged into a single process by using the "continuous" machine. Of course, it will be understood that the cloth has in each case to be cleansed from size and loose impurities. The "Mather-Thompson" Company claim that their system takes twelve hours in the case of "market" or "white" bleaching. They reckon eight hours for the steaming process and four for bleaching and washing. This has to be compared with the old system, which generally takes forty hours, made up as follows: 8 treatments with reagents and the necessary washings, the former taking four hours and the latter one hour each.
The "Mather-Thompson" system has created considerable commotion in English bleaching circles. It is generally considered that the bleachers throughout the whole country will be compelled to adopt it, so great is the saving in time and cost. In commencing a bleachery, the cost of plant by this system is, I understand, less than by the old processes. - Textile Colorist.