school system, where some hundred thousand children in the United States, breathing a pestilential air, are shrivelled by a parching heat, and doubtless lay the foundation of life-shortening diseases. The remedy should be applied by the architects; but, since few of them have properly attended to this subject, those who engage their services should oblige them to defend us from internal inclemency of the weather by suitable arrangements for heating and ventilation, as well as from external inclemency, in the buildings they construct. Beside the essays of Reid on warming and ventilation, there is a small work in Weale's Rudimentary Series, published in 1850, which may be consulted. On the warming and ventilation of the Lunatic Asylum, Philadelphia, see Journ. Fr. Inst. (3) xix. 270. 3. PYROTECHNY. The discovery of the properties of gun-cotton has led to an attempt to find other compositions to replace gunpowder, one of which we notice. A new Gunpowder.-Augendre has found that a mixture of 1 part yellow prussiate of potash, 1 part white sugar, and 2 parts chlorate of potassa, when separately reduced to a fine powder, and then mixed by hand in a wooden mortar, or larger quantities, moistened with 2 or 3 per cent. water, and mixed in a bronze mortar with a wooden pestle, and then granulated and dried in the usual way, will give a gunpowder which is readily fired by contact with an incandescent or lighted body. The mixed powders will act well without granulation. Its advantages are, that it is formed of substances of uniform composition, which are unalterable by dry or moist air; the powders may be kept separate, and mixed when wanted, and the mere mixture acting like the granulated powder; the force is greater than that of common gunpowder. Its disadvantages are that it inflames more readily than gunpowder; and it oxidizes iron barrels so much that its use must be confined to bronze metal. Gun-cotton.-According to Marx (Pogg. An. lxxviii.) the average temperature at which gun-cotton explodes is 199°, if suddenly raised, although it may explode at as low as 144°. By gradual elevation of the temperature, so as not to exceed five degrees per minute, the liability of explosion is considerably lessened. Care should be taken to pack it in vessels which will not convey heat interiorly, since metallic vessels may become heated to 144° by exposure to the sun's rays. Averos (Comptes Rendus, xxiii.) gives the following as the results of his experiments on gun-cotton : 1. Equal parts of sulphuric and nitric acids, and clean cotton. 2. Time of exposure, 10-15 minutes. 3. The mixture may be used again. 4. The cotton should not project above the liquid. 5. It should be slowly dried, and not exposed to a heat above 212°. 6. The cotton acquires more force by impregnation with saltpeter. Explosive paper is prepared, according to Pelouze, by dipping it for 20 minutes in concentrated nitric acid, washing it thoroughly with water, and drying it at a gentle heat. It takes fire at 356°, and explodes with great violence, leaving no residue. 24 21 24 16 Cotton has the formula C,H,,O,,, and gun-cotton CH1N, 011=CH1018+5NO,. Hence, 5 eq. water (HO) are removed from cotton and replaced by 5 eq. nitric acid; or H, are 16 H.. removed and replaced by 5NO, thus, C (NO) 021 1 grm. gun-cotton yields by explosion 588 cub. cent. gas (at 32° and 0.76 pressure), which has the following composition by volume: 17.03 carbonic acid. 47.45 carbonic oxide. 20.41 nitric oxide. 6.75 nitrogen. 8.36 carburetted hydrogen (CH). Charcoal.-Violette has applied highly heated steam to char wood, for the purpose of making a superior charcoal adapted to the manufacture of common gunpowder. The wood being enclosed in a cylinder, concentric within another which is heated, the steam from a low-pressure boiler is highly heated in a tube-coil, in the same fire which heats the cylinder, and enters the outer cylinder at one end, from which it enters the wood and expels the more aqueous and less combustible volatile portions. A black or red coal is produced, according to the heat and length of exposure to the steam. (Lond. Journ. 50. 1849, and J. Fr. Inst. (3) xvii. 281.) Pure Oxygen.-According to Poggendorff, Chevreul, and Vogel, the oxygen made from commercial chlorate of potassa always contains chlorine derived from some perchlorate in the original salt. After repeated crystallizations the chlorate will yield pure oxygen. (Buch. Rep. iii.) Preventing and extinguishing Combustion.-To render combustible substances incapable of combustion, at least incapable of spreading fire, is evidently a desideratum, and various substances have been proposed at different times to effect this result. In most cases they have been solutions, which are applied to the surface of wood, &c., and penetrate it but a short depth, or not at all. Of these, silicate of potassa (soluble glass) has been most preferred. Their action is, however, limited to the prevention of inflammation from sparks falling on a surface thus prepared. R. A. Smith (Phil. Mag. xxxiv. and Amer. Journ. 2d ser. viii. 118) proposes impregnating wood, &c. with a solution of sulphate of ammonia, which, if heated, is resolved into sulphurous acid, nitrogen, &c., which would tend to extinguish commencing combustion. The following composition, among others, has been given for extinguishing fires: a mixture of 1 part powdered sulphur, 1 part red ochre, and 6 parts copperas, added to the water of a fire engine is said, from experiment, to do five times as much execution in extinguishing fire as water alone; it also diminishes the annoyance of smoke and steam. It doubtless operates in a large measure from the evolution of sulphurous acid, but it is probable that anhydrous sulphuric would also be evolved. Fire Extinguisher.-Phillips has invented an apparatus (Rep. Pat. Inv. Sept. 1850; Chemist, 1850, and Pharm. Jour. x.) for extinguishing fires by gases incompatible with combustion. It consists of an iron cylinder, 2 feet by 8 inches, having at its bottom a shallow chamber filled with water. There is also a smaller cylinder, connecting at the side, and enclosing a brick composed of nitre, charcoal powder, and sawdust. In the brick is a vial with two compartments,-the upper containing oil of vitriol, and the lower a mixture of chlorate of potassa and sugar. A plug is fitted into the cover of the apparatus in such a position that a sudden blow may cause it to crush the vial and thus ignite the contents. An instantaneous and forcible issue of carbonic acid and oxide, steam and nitrogen follows, and this stream of vapor, directed upon the blazing fire, smothers and extinguishes it. Experiments have proved that this arrangement is not effective in open places, where the current of air is very strong. It may, however, be serviceable in confined places, such as the hold of a vessel. C II. PLASTICS. 1. VITRIFICATION, OR GLASS-MAKING. WE offer a few points in relation to glass, plain and colored, and introduce, also, the subject of gems, as most allied to glass. Bohemian Glass.-The glass of which combustion tubes are made has been examined by Ronney, and found to consist of: Optical Glass.-Maes and Clémandot (Comtes Rendus,1849), having studied the influence of borax in the manufacture of glass, have announced that the borosilicates of potassa, with lime, soda, or zinc, are eminently suited for optical purposes, owing to their remarkable hardness and transparency. Colored Glass.-See an excellent essay by Bontemps, on the substances used for colored glass, in the Phil. Mag. (3 ser.) XXXV. 439. Aventurine Glass.-Wöhler and others analyzed this glass, which comes from Venice; but Fremy and Clémandot have lately imitated it. (Comptes Rendus, Février, 1846.) They heated a mixture of 300 pts. powdered crystal glass (glass with a less portion of lead than flint-glass), 40 pts. suboxide |