A modification of the same problem is constantly occurring to practical science, and its almost uniform solution shows that our world has been arranged with a benevolent eye to the growing comfort of the greater number. Science is perpetually importuned to cheapen commodities; and by substituting a simple method for an intricate process, or by making a common material fulfill the part of a rare one, it is every year giving presents to the poor. Few substances are more essential to our daily comfort than soda. It is a large constituent of glass and soap, and many other useful articles. The cleanliness of a nation depends on the cheapness of soda; and if soda is cheap, you can substitute plate-glass for crown in your windows, and you can adorn your apartments with glazed pictures and mirrors. So that from the bleacher who spends thousands-a-year on the carbonate, to the apprentice who in the dog-days lays out a penny on ginger-beer or soda-water, all are interested in the cheapness of soda. But this alkali used to be dear. Small quantities were found native, and larger supplies were obtained from the burning of sea-weed. Still the cost was considerable. However, it was well known that a vast magazine of the precious article surrounds us on every side. The sea is water changed to brine by a salt of soda. If only a plan could be contrived for separating this soda from the hydro-chloric acid, which makes it common salt, there is at our doors a depot large enough to form a Mont Blanc of pure soda. That plan was discovered; and now a laundress buys a pound of soda (the carbonate) for three half-pence, and the baker of unfermented bread can procure the more costly bicarbonate for sixpence. Lately, if not still, in the shops of provincial apothecaries, no article was in such demand as one styled in the Pharmacopœia, muriate of magnesia. This popular medicine was first obtained by evaporation from certain mineral waters, and as the supply was limited the price was high. But few ingredients could be cheaper than the earth and the acid from which it is combined. The earth forms whole mountains, and the acid is that cheap one set free when the soda is separated from common salt. Accordingly, chemists went to work, and in their laboratories did what the mineral spring had been doing since the Deluge, and by a simple process they manufactured the muriate of magnesia. A few years ago, looking at the remarkable rocks of magnesian limestone which defend the Durham coast, near Shields, our companion remarked, “Many a hundred tons of these rocks have we converted into Epsom salts!”