BLAYE BLEACHING 703 lews. The work has been in satisfactory pro- gress since the summer of 1869, with the excep- tion of one interval, when the available funds were exhausted ; but the appropriations have never been nearly equal to what could have been economically expended. The Burleigh drill has been in constant use, but hand drills are also worked with great advantage, as in the progress of the work it is found expedient to use many small blasts of giant powder. When the excavation is completed it is designed to intro- duce an explosive compound into the columns and various parts of the roof, and produce a simultaneous explosion with a galvanic current. Topographical surveys are continually made during the progress of the work to determine the direction and extent of the excavation, the usual methods of triangulation and levelling be- ing employed. There have been 21,000 sound- ings and 8,000 borings of the bed of the river, for the purpose of ascertaining the depth of live rock. No accident has happened with the use of nitro-glycerine, owing to the care with which it is prepared, and the prudence with which it is handled. With regard to the preparations of nitro-glycerine, dynamite or giant powder is considered by those who use it to be a safer explosive than gunpowder. Dualline, which is a somewhat similar preparation, has also been used with satisfactory results. The danger in using nitro-glycerine arises principally from the collection of vapors liable to take place when it is confined. BLAYE (anc. Blama), a fortified town of France, in the department of the Gironde, on the right bank of the river Gironde, 20 m. N. by W. of Bordeaux ; pop. in 1866, 4,761. The upper part of the town, with the citadel, lies on a steep rock ; hi the citadel, which was built by Vanban, the duchess of Berry was im- prisoned in 1832. On the opposite side of the river is Fort M6doc, and on an islet between them is a fortified tower called the Pat6 de Blaye. The town has been a military station since the times of the Romans. It has a school of hydrography and an active coast trade. BLEACHING, the process of removing colors from fabrics and raw materials and leaving them white. The principal substances to which bleaching is applied are wool and silk, in the animal, and cotton, flax, and straw, in the vegetable kingdom. The coloring matter in these bodies is not essential to their texture, and fortunately can be removed by chemical agents without injury to the structure of the rest of the material. Steeping cloths in lyes extracted from the ashes of plants, and after- ward repeatedly washing and exposing them to the action of sunlight, was practised by the ancient Egyptians ; but nothing more than this is known of their process. There was scarcely any progress in the art for thousands of years, or until the 18th century, when somo improve- ments were made in Holland. The Dutch pro- cess consisted in pouring the alkaline solution over the goods in a boiling condition, and 97 VOL. ii. 45 steeping them in it for about a week, and, after washing, again steeping them for another week in buttermilk. After this they were thoroughly washed and exposed to the action of the air and sunlight for several months. These apparently simple processes obtained for the Dutch a high reputation for bleach- ing, and gave them almost a monopoly of the business for very many years. For a long period the brown linens manufactured in Scot- land were regularly sent to Holland to be bleached. A whole summer was required for the operation ; and if the cloths were sent in the fall of the year, they were not returned for 12 months. It was this practice which caused the name of hollands to be given to these linens. The Scotch introduced the business of bleaching for themselves about the year 1749; but it was long believed that the peculiar properties of the water about the bleaching grounds of Haarlem gave to this neighborhood advantages which no other re- gion could possess. The precise chemical ac- tion that takes place in the process of bleach- ing is not known with certainty, but it is probably due to the action of oxygen when it is in a nascent state, or in that peculiar and active one called ozone. The investigations of Schonbein have proved that atmospheric oxy- gen, under the influence of sunlight and moist- ure, passes into an active state, thus explaining the rationale of the old bleaching process. Bleaching by chlorine involves the abstraction of hydrogen from the coloring matter, and the momentary freeing of a portion of oxygen, which enters into a new combination by which it is thought the bleaching is effected. The action of sulphurous acid, which is usually a deoxidizing agent, does, however, according to Schonbein's investigations, on exposure to the air and light, bring a portion of atmos- pheric oxygen into an active condition. Chem- ists, therefore, attribute the action of all bleaching agents to the power they possess of causing oxygen to pass into its active state. The art of bleaching was conducted by alter- nate steeping in alkaline liquors called buck- ings, followed by thorough washing and boil- ing and long continued exposure upon grass, with frequent sprinklings of water, which pro- cess was called crofting; and this was followed by the souring process, or keeping the articles soaked for weeks in sour milk, to be afterward washed and crofted several times. By sub- stituting dilute sulphuric acid for sour milk to dissolve out the alkaline matters, as suggested by Dr. Hope, the time required for this part of the process was reduced to a few hours in place of a few months. But the other operations still involved long time, particularly the croft- ing; and frequent losses moreover were in- curred by the exposure of the goods in large establishments upon the great extent of grass lands they required. Of cotton goods one twentieth to one tenth of the weight is lost by bleaching ; but linens often lose as much as
