Gunpowder was first known in England about five hundred years ago. It is not only used to discharge firearms, but in the more peaceful occupations of quarrying stone, mining, and to get rid of rocks both below and above water; these processes are called “blasting.” GUN COTTON. To prepare gun cotton, make a mixture of three parts sulphuric acid and one part nitric acid; when this has cooled (for it becomes hot on mixing), put into it some cotton wool, and let it be stirred about with a glass rod, then taken out, and all the superfluous acid strained from it; it is then to be covered up for an hour or so. It should now be thoroughly washed in cold water, so that all the acid be removed; to ensure this completely, let it be afterwards washed in a very weak solution of potash, and then dried by a very gentle heat, produced by either steam or hot water; when dry, soak it in a solution of nitre and dry it again. It is now so explosive that great care is required in its management, being about three times as explosive as gunpowder. PHOSPHORUS. This substance, since the general use of lucifer-matches, has become an important article of manufacture; whereas, but a few years ago, it was a mere chemical curiosity. It is prepared by mixing bone ashes with sulphuric acid, straining off the liquid part, and evaporating it to a syrupy consistence; with this, about a quarter of its weight of powdered charcoal is mixed, and the whole stirred and evaporated to a dry powder; this is put into earthenware retorts, which are connected by copper tubes to receivers filled with water; the retorts are raised to a white heat and maintained at this high temperature as long as any phosphorous passes into the receivers, the water in which is kept warm, so that the phosphorous melts and runs to the bottom, from whence it is taken and strained through chamois leather bags, under warm water, and then cast in glass tubes into sticks. Phosphorous is of a whitish color, like wax, is easily melted, readily takes fire even by slight friction, and, in the air, gives off fumes which in the dark appear luminous. It is chiefly used in the manufacture of lucifer matches, and, mixed with flour, butter, or sugar, is used to poison rats, mice, and other vermin, under the name of “phosphorous paste.” Phosphorous is poison, and most dangerous stuff to handle, minute particles often getting under the nails and causing painful sores. WHITE LEAD. Illustration: WHITE LEAD BED. Illustration: FIG. 1. (‡ LEAD GRATE.)