A modified form of the fan, called a centrifugal disk, patented by Mr. Ramtnell, was successfully employed by the Pneumatic Dispatch Company for the transmission of the mail-bags. An ingenious but simple ventilator is in use in the mines of the Harz for supplying fresh air. It consists of two long cylindrical vessels, one of which is so much smaller as, when inverted, to move up and down inside the other. The outer one is partly filled with water, and has a tube through the water down to the mine. The inner inverted cask, which has a valve opening inwards, is lifted and then pressed down, so forcing air through the tube.
The Messrs. Roots' blowing-machine is thus described: "A pair of horizontal shafts, geared together at both ends, traverse a case of the form of two semi-cylinders, separated by a rectangle equal in depth to the diameter of the semi-cylinders, and in width to the distance between the centers of the shafts. . . . These shafts carry a pair of solid arms. each having a section somewhat resembling a figure of eight, the action of which, as they revolve, takes the air in by an aperture at the bottom of the machine, and expels it with considerable pressure, if required, at the top." For the purposes of ventilation, and also for expelling accumulations of hot air, dust waste flyings, etc.,. in factories, a machine has been constructed by Mr. J. Howorth, Farnworth, Bolton, called a rerolring Archimedcan screw-ventilator. It consists of an Archimedean screw inclosed in a tube with proper means of lubrication. Its diameter is 30 in., and it is made to be set in motion by steam or other power, but it is also fur nished with a hood, on the top of which there are curved vanes, which turn the screw by the action of the wind. Immediately beneath these, there is another series of lateral vanes for the escape of the hot air.
a small instrument used in the arts for soldering metals, and in analyt ic:41 chemistry and mineralogy; for determining the nature, of subatancea by the action of an intense and continuous beat, its principle depending on the fact, that when a jet of air or oxygen is thrown into a flame, the rapidity of combustion is inereaaed, while the effects are concentrated by diminishing the extent or space originally occupied by the flame.
The blow-pipe generally consists of a conical tube of metal, about 8 in. long, closed :it the wider or lower end, but open at the narrow or upper end, which latter constitutes the mouthpiece, and Is turned over tot:Willit of the lips closing perfectly round it. Near
the lower evil, a small tube, titled with a finely perforated nozzle, is inserted at right angles to the large tube, the space below being intended as a chamber for condensing the inoisture.of the breath. Through this nozzle, a title current of air can be projected agssinst the flame experimented with.
When a current or air from the blow-pipe is direeted against a candle or gas-jet, the flame ahnost entirely loses its luminosity, OWIng to the perfect combustion of the gases evolved from the source of beat, and is projected in a lateral direction, as a long-pointed cone, consisting of three distinct parts. The first or central cone is of a dark-blue color, and there the combustion is complete from the excess of air thrown in from the small nozzle, The second cone, or that immediately surrounding the first, is somewhet luminous; and here the oxygen, being insullicient for the combustion of the carbon, any metallic oxide subjected to the action of this portion of the flame is deprived of its oxygen, and redisced to the condition of metal: for this reason the luminous cone is generally termed the reducing flame of the blow-pipe. Beyond the second cone, or where the flame comes freely in contact with the atmosphere, and abundance of oxygen is present to effect complete combustion of the gases, is 11 third, or pale yellow envelope, containing excess of atmospheric air at a very high temperature, so that a portion of metal, such as lead or copper, placed at this point, becomes rapidly converted into its oxide: thisouter part of the flame is on this account called the oxidizing flame of the blow-pipe.
Substanees under examination before the blos•-plpe are generally supported either on wood-charcoal or platinum—the latter in the condition of wire or foil. 10 applying the blow-pipe test, the body to be examined is either heated alone, or along with some fax or fusible substance; in some cases, for the purpose of assisting in the reduction of metals from their ores and other compounds; in others, for the production of a transparent classy bead, in which different colors can he readily observed. When heated alone, a Iw) of platinum wire, or a piece of charcoal. is generally employed as a support ; the former when the color Of the flame is to he regarded its the c1lal'Ilcteristic reaction, the latter when such effects as the oxidation or reduction of metallic substances are to be observed.