II. Pure carbonate of soda, or the mineral alkali, so much resembles the vegetable alkali, when used as an agent in bleaching, that little difference is observable in its effects when the strength of the alkaline leys and every other circumstance are the same. The high price at which soda has hitherto sold, has pre vented its being generally used at the bleachfield ; but since more economical processes are adopted in the manufacture of it, and since it is made in a greater degree of purity, its introduction into the bleachfield will naturally follow. It is admirably cal culated, as a detergent, for the finishing of the finer fabric of muslin ; it being ascertained beyond doubt, that 6 ounces of pure carbonate of soda, together with 10 ounces of soap, produce effects in bleaching equal to I; pounds of soap, when used by itself.
2d, Barilla, as imported from Alicant in Spain, is in large masses, of a dark gray colour. It usually contains from 20 to 24 per cent. of pure mineral al kali, and never above 33 per cent. when in a state of the greatest purity. The remainder of the mass usual ly consists of sulphate and sulphite of soda, with a large proportion of charcoal and common salt.
The best method of extracting the soda from ba,. cilia, is to pound it, and fill a large wooden vat with it, the bottom of which has been previously covered with straw, to act as a filter ; the vat is then filled with cold water, which is allowed to remain for some time to dissolve the salt. When sufficiently strong for use, the solution is run off at the bottom of the vessel by a stopcock, by which means it is freed. from the charcoal and other impurities. Fresh water is again poured on the barilla, until the whole of the salt is dissolved. By this operation the soda is ex tracted, which being a very soluble salt, is easily dis solved by the water ; but, at the same time, the com mon salt, which is equally soluble, together with a portion of the sulphate of soda, is also dissolved, which contaminate the solution, and have no effect as detergents. On this account, pure soda is cer tainly preferable for bleaching, (when it is not too high priced,) as it contains none of the foreign salts contained in barilla, which retard in place of promo ting the process of bleaching. The bleachers in Ireland fs;rtru_rly used large quantities of barilla, but its use is now almost universally given up, potash being substituted in its stead.
3d, Kelp would be iinWorthy of notice, were it not that it is still recommended by some as a deter gent in bleaching.
As at present manufactured, kelp is very inferior in this respect : The very best Scotch kelp never con tains above 7 or S per cent. of mineral alkali, but more commonly from 3 to 5 per cent. Considering the other impure substances contained in kelp, it is at present unworthy of attention. But there is no doubt, that if proper methods were adopted for the manufacturing of it properly, it may be very much improved in quality. In the present rude manner in which it is made, the marine plants called Fucus Serratus and Fucus Vesiculosus of Linnaeus, being cut at midsummer, and dried by the sun and air, are burnt in holes made in the sea beach : when a large portion of it is burnt together, part of the salt fused by the strong heat combines with sand, and other earthy matters, and forms an imperfect glass. In a furnace properly constructed, with a graduated heat, we htive known kelp made of a quality far superior to the very best of that which is made by the com mon process.
It. has been suggested, that were the sea plants, from which the kelp is made, previously washed in fresh water before they are dried, they would thereby be freed from a large portion of marine acid ad. hering to them, which remains undecomposed during the burning of the plant when it is converted into kelp. This theory supposes, that the plant, during the pro gress of its growth, has the power of decomposing the sea-water, and retaining soda as one of its component parts : and that if this be the case, and if the com bustion of the plant were properly conducted, a salt nearly equal in value to barilla would be the pro duct. These facts may be easily proved by those who have skill to ascertain, and opportunity to in vestigate, a matter which is of considerable national importance.
In order to ascertain the quantity of real alkali contained in the different detergent salts used in bleaching, M. Descroizilles sen. employed the me thod before mentioned, by saturating a given quan tity of the alkaline salt with diluted sulphuric acid, the specific gravity of which was always the same.
After many thousand trials during the course of 25 years practice, the following are the mean results : Hence it appears evident, of what importance it is . to bleachers, and others who use alkalis in any quan tity, to have it in their power to ascertain the quan tity of pure salt contained in them ; as, by a proper knowledge of this,great saving may be made by them in the course of their business.