364 BLEACHING 



out u]pon the ground to bleach. It must bo remarked that after every dipping the 

 cloth is washed first with black soap, then with clear water, and after each of the 

 operations it is wrung by means of a machine that turns by means of a wheel. 

 .... The whitening grounds are cut with canals in some places, that there may be no 

 trouble of fetching water from a distance. The cloth is watered with long narrow 

 shovels made in shape of a scythe. The water of these canals comes from the dams, 

 and it is that which contributes most to the lustre of the Dutch cloth. To prevent 

 the water from becoming thick and muddy, they are extremely careful in cleaning 

 these canals. The washing tubs are built with bricks, with two trap-doors or sluices 

 for admitting or excluding the water according as it is necessary.' Select Essays, 

 quoted by Parko. 



The chief advantage here consists in the facility of obtaining soap, which in ancient 

 times was either scarce or badly made. This improvement began to be more and 

 more used from the time of its earliest introduction. Modern times have begun to ex- 

 clude it to a great extent again, finding it so much cheaper to work with the alkali 

 alone without combining it with fatty matter. 



The process of bleaching then became a series of operations, consisting of, 1st, 

 steeping in water for about three or four days, or in weak alkali for forty-eight 

 hours. 2nd, boiling in an alkaline lye, or, in other words, bucking or bowking : in 

 this operation the hot lye was poured on the cloth ; it then ran through it, was drawn 

 off by a tap below, and then pumped up again. 3rd, crofting, or exposure to sun and 

 air on the grass. 4th, souring : this was done by the butter-milk ; it lasted several 

 weeks. These operations were repeated four or five times, or until the goods were 

 pure. The whole lasted from March to September. The bes months for crofting 

 were found to be March, April, and May. It was not known that it was the acid of 

 the butter-milk which acted ; but when sulphuric acid became cheaper, Dr. Home 

 applied it instead of butter-milk, and caused a great revolution in bleaching, as the 

 souring could now bo done in a day which before had occupied weeks, exposing the 

 cloth to much danger of decay by decomposition or putrefaction. Great fear was 

 expressed in the country lest the vitriol should burn the cloth, when Dr. Home stated 

 that he had kept linen in acid of the required dilution for some months without 

 having it injured. Berthollet also said that the acid made a better white. 



In 1784 Berthollet made known some investigations on chlorine, and in 1787 

 communicated them to the French Academy. By these investigations it was found 

 that chlorine had the power of destroying colouring-matters. The use of chlorine 

 was brought to this country by the Duke of Gordon and Professor Copeland of 

 Aberdeen, who then gave the process to be carried out by Messrs. Milnes, of the firm 

 of Gordon, Barron, and Co., of that place. In this discovery the theoretical portion is 

 due, first, to Scheele, who discovered the chlorine ; and, secondly, to Berthollet, who 

 discovered the peculiar property. The practical mode of effecting the object is the 

 part which we claim ; but it consists of such a long series of expensive trials and 

 ingenious contrivances, that it will take a much longer time to describe them than 

 to give the first idea only. As the invention was at first applied only to cotton, 

 which at that period was rising into importance, we shall begin the description of 

 modern bleaching with the mode adopted for that material. 



James "Watt at the date given was in intimate communication with Berthollet, and 

 did not rest until he had made the process successful at the bleach-field of Macgregor, 

 near Glasgow, requesting the results to be communicated to a meeting of manufac- 

 turers to be called together at Manchester ; so quick was Watt to see what would be 

 for the permanent interest of a country, and so ready to act on it ! Dr. Henry did 

 much to make it known to the manufacturers about Manchester. This is one of the 

 early instances of scientific men being directly applied to by manufacturers for as- 

 sistance an application seldom made unless under great difficulties. 



In 1798, Charles Tennant, of Glasgow, introduced chloride of lime, which is pre- 

 ferred above all other compounds as a means of applying chlorine. 



The true theory of bleaching has not been entirely agreed upon, but there can bo 

 little doubt of the principal operations. It is known that oxygen deprives substances 

 of colour; this may bo performed by many high oxides; by nitric acid, manganic 

 and chromic acids, chlorous acid, and oven lower oxides which hold their oxygen 

 lightly, as hypochlorous acid. The same effect may be produced by chlorine, bromine, 

 and iodine. It has been said that chlorine unites with the hydrogen of the water 

 which is present, gives off oxygen, and so acts .just as oxygen would. Davy found 

 that it would not act in dry air, so that water was needful : but Dr. Wilson found 

 that it would act, although slowly, in dry air, if exposed to the rays of the sun. This 

 might show that water is not necessary in order to supply oxygen, but only to allow 

 the chlorine to be brought into thorough contact with the colouring-matter. It has 

 also been supposed that the chlorine removes the hydrogen, or, rather, simply takes 



