gress. When the lamp is newly lighted and the furnace cold, the oil should be passed slowly in distinct drops; but as the furnace becomes heated the rapidity of the supply of drops should be increased; and finally, when the furnace is at a white heat, the oil should be supplied in a thin continuous stream. When the fusion to be effected is that of only a small quantity of metal, such as 1 lb. of iron, a rapid supply of drops of oil is sufficient even to the close of the operation. At that rate the burner consumes about 14 pint of oil in an hour. When the fusion to be effected is that 4 lbs. or 5 lbs. of iron and the large furnace is in action and has been brought to a white heat, the supply of oil must, as stated above, be in a thin continuous stream, and the operation will then consume two pints of oil in the hour. And here it requires remark that, with that continuous supply, when the furnace is large and is at a white heat, the oil does not rise in the funnel, being instantaneously converted into gas at the mouth of the burner, and thrown up in that state into the furnace for combustion. The operation, indeed, consists at that point of a rapid distillation of oil-gas, which is immediately burnt, in the presence of air supplied at a suitable pressure by a dozen blowpipes, in effective contact with the crucible to be heated.

The flame produced in this furnace is as clear as that produced by an explosive mixture of air and coal-gas. It is perfectly free from smoke, and the consumed vapours which occasionally escape with gaseous products of the combustion, are even less unpleasant to smell and to breathe in than are those which are usually disengaged by a blast gas furnace, or by an ordinary lamp, fed with pyroxylic spirit.

The contents of a crucible under ignition in this furnace can at any moment be readily examined, it being only necessary to remove the pieces I and m with tongs, and to lift the cover of the crucible, during which the action of the furnace need not be interrupted.

When the operation is finished, the blast is stopped, the stop-cock is turned off, the oil-reservoir is removed, the wick-holder is lowered on the support o, withdrawn from the furnace, and covered with the extinguisher n. The

quantity of oil which then remains in the lamp is about one fluid ounce.

POWER OF THE OIL-LAMP FURNACE.-The furnace being cold when an operation is commenced, it will melt 1 lb. of cast iron in 25 minutes, 1 lb. in 30 minutes, 4 lbs. in 45 minutes, and 5 lbs. in 60 minutes. When the furnace is hot, such fusions can be effected in much less time; for example, 1 lb. of iron in 15 minutes. It need scarcely be added, that small quantities of gold, silver, copper, brass, German silver, &c., can be melted with great ease, and that all the metallurgical and chemical processes that are commonly effected in platinum and porcelain crucibles can be promptly accomplished in the smallest cylinder of this furnace; and in the case of platinum vessels, with this special advantage, that the oilgas is free from those sulphurous compounds the presence of which in coal-gas frequently causes damage to the crucibles.

REQUISITE BLOWING POWER.-The size of the blowingmachine required to develop the fusing power of this oil-lamp furnace depends upon the amount of heat required or the weight of metal that is to be fused. For ordinary chemical operations with platinum and porcelain crucibles, and even for the fusion of 1 lb. of cast iron in clay or plumbago crucibles, a blowing power equal to that of a glass-blower's table is sufficient, provided the blast it gives is uniform and constant. But the fusion of masses of iron weighing 4 or 5 lbs. can be effected by the gas which this oil-lamp is capable of supplying, provided a sufficiently powerful blowingmachine supplies the requisite quantity of air. When more than a quart of oil is to be rapidly distilled into gas, and the whole of that gas is to be instantly burned with oxygen, it is evident that effective work demands a large and prompt supply of air.

As in all practical matters of this sort, the cost is a main question, it may be useful to state that the price of this apparatus complete, without the blowing-machine, but including every other portion necessary for heating crucibles up to the size sufficient to fuse 1 lb. of cast iron, is one guinea; and that, with the extra furnace pieces for crucibles suitable for 5 lbs. of iron, or any intermediate quantity, the cost is one guinea and a half.

GAS BLAST FURNACE.-The furnace (shown at fig. 33) is suitable for the fusion of refractory metals, and for all purposes of ignition, combustion, fusion, or dry distillation at a red or a white heat, where it is desirable to produce those temperatures and effects promptly, steadily, and conveniently. This furnace has also been devised by Mr. Griffin.

It consists of two parts: firstly, of a particular form of gasburner, which is supplied with gas at the usual pressure, and with a blast of common air, supplied with bellows or a blowing-machine, at about ten times the pressure at which the

gas is supplied; secondly, of a furnace which is built up round the flame that is produced by the gas-burner, and the crucible that is exposed to ignition. The object of the peculiar construction of this furnace is to accumulate and concentrate to a focus the heat produced by the gas-flame, and to make it expend its entire power upon any object placed in that focus.

The gas-burner is a cylindrical iron reservoir, constructed as shown in fig. 34, which is drawn on a scale of one-third the full size. It contains two chambers, which are not in communication with one another. Into the upper chamber, gas at ordinary pressure is allowed to pass by the tube marked GAS. Into the lower chamber, air is forced by the tube marked AIR. The upper part of the burner is an inch thick in the metal. Through this solid roof holes are bored for the escape of the gas. The experiments described hereafter were chiefly made with a burner that contained sixteen holes, arranged as shown in fig. 35, which is a surface view of the burner represented by fig. 34. But burners with three holes, six holes, and twenty-six holes, have been made for other purposes. The number of holes depends, of course, upon the heating power required from the burners. The air passes from the lower chamber, through a series of metal tubes placed in the centre of the gas-holes, and continued to the surface of the burner, so that the gas and air do not mix until both have left the gas-burner, and then a current of air is blown through the middle of each jet of gas. The bottom of the gas-burner is made to unscrew, and the division between the two chambers which carries the air-tubes is easily removable for the purpose of being cleaned. The gas and air pipes are both half an inch in the bore, and may be about ten inches long; the gas should have a pressure of half an inch of water, and the blast of air about ten times that pressure. The quantity of gas used in an hour is about 100 cubic feet. The stop-cock which supplies it has a bore of half an inch. The round rod which is represented at the bottom of the burner, fig. 34, is intended to fit it to the support, shown by b, in figs. 36 and 41.

When the gas is lighted and the blast of air is put on, the flame produced by the gas-burner is quite blue and free from smoke. It is two inches in diameter, and three inches high, and the point of greatest heat is about two inches above the flat face of the gas-burner. Above this steady blue flame there rises a flickering ragged flame, several inches in height, varying with the pressure of the gas. In the blue flame thin platinum wires fuse readily.

When the gas is burning in this manner, and the apparatus is attached to flexible tubes, the burner may be inverted or held sideways, without disturbing the force or regularity of the flame, so that the flame may be directed into a furnace at the bottom, the top, or the side, as circumstances may require.

The following articles are used in building up the gas furnace for different experiments. They vary in size according to the volume of the crucible, or the weight of the metal which is to be heated.

A circular plate of fire-clay, two inches thick, with a hole in the centre, exactly filling the upper part of the gas-burner, which is made to enter into the hole three-quarters of an inch. In external diameter this clay plate agrees with each size of furnace.

A cylinder of fire-clay, of which two pieces are required to constitute the body of each furnace. In the middle of each cylinder a trial-hole is made, one inch in diameter, to which a fire-clay stopper is adapted. (See fig. 36.)

A fire-clay cylinder, closed at one end, and pierced at the open end with numerous holes of half an inch in diameter. The thickness of the clay is immaterial. There are several sizes of this cylinder for crucibles of different diameters. It is represented at a, fig. 37.

A circular plate of fire-clay from two to four inches in diameter, and one inch thick. Similar pieces half-inch thick are useful.

Cylinders of plumbago, pierced with numerous holes of three-eighths of an inch in diameter. Their use is to support flanged crucibles over the flame.

A cover or thin plate of plumbago, three inches in diameter. It has a small hole in the middle, and being of a soft material, the hole can be easily cut or filed to suit crucibles of any desired size, so as to support them on the cylinder.

As in all cases the heating power of the gas furnace spreads laterally, and does not rise vertically, the most advisable form of the crucibles required for use in it is short and broad, not tall and narrow, and the supporting cylinders must be shaped