History and Art of Bleaching.

Scientific American 5, 2.11.1861

A very interesting paper was read upon this subject before the late meeting of the British Scientific Association, by Mr. Henry Ashworth, the substance of which, together with some comments, we herewith present.

The art of bleaching cloth dates from the earliest ages of industrial art. It first commenced in the family, and was accomplished with soap and water, the friction of female hands and exposure to the sun's rays, moisture and the atmosphere. The whitening effecy of the sun's rays upon green cloth sprinkled occasionally with soft water is well known to every good housewife. Previously to the middle of the last century the cotton manufacture was scarcely known. Holland was for many years the bleaching house of England. Webs of brown linen used to be sent by English and Irish weavers to Holland to undergo bleaching, and at the end of the short space of eight months they were returned finished. In 1749, an improvement took place in bleaching by boiling cotton and linen cloth, first in water containing some slacked lime, then steeping it in an alkaline lye, after which the cloth was washed, then steeped in sour milk, and afterward exposed on the grass to sunshine and moisture, called "crofting", for about ten weeks. An improvement was made upon this process by Dr. Home, of Edinburgh, who substituted dilute sulphuric acid for the sour milk. But the greatest improvement made in the art of modern bleaching is due to M. Scheele, a Swedish chemist, who discovered chlorine in 1787, and used it as a substitute for the exposure of the cloth to the atmosphere. The celebrated French chemist, Berthollett, (who is so well known for his treatise on dyeing) by experiments in his laboratory in Paris, soon afterward more fully developed the virtues of chlorine as a bleaching agent, and to James Watt, the inventor of the steam engine, the chief credit is due for the introduction of chlorine into Great Britain. When on a visit to Paris, Berthollett gave Watt information how to generate chlorine, and he described to him its whitening powers. On his return to Scotland, he generated some of the gas and experimented with it in the Bleaching Works near Glasgow, and he ceased not his labors until they were successful. It has been stated that he was the first person who applied chlorine to the practical arts. This bleaching gas was then generated in long bottles and used in a solution of potash. An improvement was made in 1789, upon this process of obtaining and using the chlorine, by Charles Tennant, of Glasgow, who used a saturated solution of chloride of lime. This invention he secured by patent, but the bleachers and calico-printers of Manchester, England, resisted his patent, on the ground of a flaw in the specification, and they were successful. Subsequently he made the discovery that quick dry lime also absorbed chlorine gas, and this he secured by a carefully drawn up patent, which afterward made him a millionaire. He then commenced the manufacture of chloride of lime, called "bleaching powder", and it was soon used to the exclusion of all other combinations for bleaching, and is so now throughout the world. Chlorine possesses the solvent power of destroying vegetable colors. It is this chemical quality applied to bleaching cotton and linen which has reduced the tedious operations connected with the art from weeks to hours in point of time. And the prices for bleaching have also been reduced in the same ratio, thus benefiting all classes. In 1803, the price charged in Manchester for bleaching and finishing 21 yards of cotton cloth was seven shillings and sixpence (about $1.80), now it is only sixpence (about 12 cents), or one-fifteenth of the price charged fifty-eight years ago.

In preparing cloth for bleaching, if it be intended for calico-printing, its surface nap is singed off; if not intended for printing, however, it need not undergo this process. The first operation consists in boiling the cloth for several hours with milk of lime in a "bucking keer," after this it is washed, then run through a dilute sour of sulphuric acid and water, then washed and submitted to successive steepings in cold chloride of lime liquor and weak sour until it is quite white. This occupies several days according to the strength of the steeps, but by using warm, strong liquors, it may be bleached white in half an hour. This quick process would not be so favorable for the strenght of the fabric. The folloring is a description of the mode of operations pursued at the Lowell (Mass.) Bleach Works:
- 1st. The cloth is steeped for about twenty-four hours in tepid water.
2d. It is passed through a bath of milk of lime (fresh slacked lime and water).
3d. Boiled in lime water for six hours.
4th. Washed.
5th. Soured in dilute sulphuric acid at 2° Baume.
6th. Washed. 7th. Boiled for six hours in a solution of carbonate of soda and resin, previously dissolved in alkali.
8th. Washed.
9th. Passed through a clear solution of the chloride of lime marked 1° Baume.
10th. The cloth is exposed folded in the machine in pits with open sides, where it is exposed to the action of carbonic acid and air while it is still saturated with the chloride of lime.
11th. It receives another sour of 2° Baume, then two washings in a machine, and it is ready for drying and finishing.
This is the method which is described in the new "American Cyclopedia." In other bleach works in America the process is somewhat different, there being two immersions in chloride of lime and hydro-chloric acid (muriatic acid alias spirit of salt), used in place of sulphuric acid for the sours. The soda and resin solution produces a semi-soap liquor, which forms part of the system patented some years since by Mr. Higgins, of Manchester, England.

In the mechanical and manual operations of bleaching as great a revolution has been effected as in the chemical actions and processes. In the days of grass bleaching, the crofters - men and women - were constantly exposed to moisture in wheeling wet pieces of cloth on barrows, and carrying them on their shoulders to the grass fields. They were seldom dry, and during the cold days of winter their clothes were frequently frozen on their persons. The life of the field hands was then a woarisome drudgery, and their wages were exceedingly low. Machinery has now taken the place of most of the hand labor; there is no more ourdoor work in wet weather; the labor is now light and the pay much higher. In England, Mr. Ashworth states, that the staple food of the bleacher was formerly oatmeal, and animal food, with the exception of bacon, was seldom found in their tables. The times have changed for the better. Processes and machinery have been improved; toil is made more healthy and comfortable, and the social condition of the operatives has advanced in an equal degree. "Their tables are now spread with wheaten bread, animal food, an all the other articles which usually enter into the consumption of families in the other grades of life."

In the finishing operations of bleached cloth there is great rivalry among the different establishments in England, and to such an extent has this competition been carried that "the machinery, skill and cost of extraneous materials required have occasioned an expenditure that is said to exceed all the other expenses in bleaching." In America there is but little rivalry of this sort, and out of France, Scotland and Switzerland, the finishing of the finer fabrics (such as muslins) of bleached cotton cloth is but little understood and practiced.