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The Blowpipe Lamp,-Fig. 3,-has a headpiece of the same shape as that used by BERZELIUS. It is made of iron plate, tinned over, and varnished black. As a greater

Fig 3.

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proportion of substance is used in a quantitative than in a qualitative analysis, and also a stronger heat is required, the socket in the lamp is wider than usual, so that the flame of the Blowpipe may be deflected to any desired point,-Fig. 6, p. 11.

The brass ring encircling the socket, must not be too distant or elevated, as is the case with those lamps which have the top screwed to the ring. In this lamp, the screw is affixed to the external part, so that a cover can be placed over it, which, below, is provided with a large margin of brass, having fastened to it a piece of leather, which can be placed over it. The leather is attached in the following manner :-First, that side which is not to be cemented to the brass rim, must be covered over with molten wax, and when it hardens, the other side must be varnished with a strong solution of shell-lac in alcohol; over the brass edge rub also some of the solution, and then keep the leather pressed upon it for some time. When the spirit has evaporated, the shell-lac remains as a durable cement. screw in the lamp does not permit a drop of oil to escape.

The

If a separate opening for pouring in the oil be made at the upper part of the lamp-B-according to the proposal of HARKORT, it must be wide enough to enable the operator to ascertain how high the liquid reaches. A screw can also be adapted to this opening, as the figure in the drawing shows.

The wick must be cotton; and, before it is immersed in the oil, it should be folded together three or four times, and then cut parallel with the oblique side of the socket to allow the flame to be easily directed downwards.

The lamp for experiments may be placed on the brass stand A, and fastened by a screw a, to the brass pillar.

On the same apparatus may be adapted a brass triangle c, containing three bars of different lengths, and a movable arm. This triangle serves as a support for drying or fusing any article over the flame of an oil or spirit-lamp.

A small spirit-lamp may be profitably used for heating substances, containing volatile ingredients, in glass tubes or alembics, and for melting various assays with bisulphate of potassa in the platinum spoon, et cetera. For

Fig. 4.

this purpose BERZELIUS used a small phial of strong glass, with a ground top, in which is inserted a tube of silver or iron, for containing the wick. Fig. 4 shows a vertical section of such a lamp, which is about one and a half inch in diameter. Although a small brass lamp of another form is sometimes used, still, the glass one, if carefully handled, is in every respect preferable.

III. THE BLOWING, AND DESCRIPTION OF THE FLAME.

The air of the Blowpipe is obtained from the mouth, and not from the respiratory organs, because they could not, without fatigue, afford a sufficient stream. The current of air is forced through the tube by the action of the Musculi Buccinatores, which are in the cheeks. During the blast, the communication between the chest and mouth is closed, so that respiration is carried on through the nostrils.

Until a person is accustomed to the use of this instrument, a strong and uninterrupted stream cannot be obtained; but after a few days' practice the process becomes easy. The fear of blowing being injurious to health is soon removed.

Fig. 5.

To obtain an intense heat by blowing on the lighted combustible, requires a previous knowledge of its various parts; for on examining the flame of a lamp which does not emit smoke, it will be found divided into many. This appearance is more clearly to be seen in the flame of a wax or tallow candle, where four distinct portions are noticed. Fig. 5 represents a flame a fine clear blue color is visible at a b; this azure tinge surrounds the burning wick, but becomes less distinct as it ascends, and, where the flame elongates perpendicularly is wholly diffused. In the cen

tre of the flame is a very dark conical portion c; this part is encircled by d, the sphere whence nearly all the light emanates: external to this is a, e, b, which part affords scarcely any light, but gives out more heat than any other. The hottest part of this exterior flame is at f; the heat diminishing towards the

summit e, and base a b. When a very fine iron wire is introduced horizontally into the flame, it expands and becomes of a white heat, at the outer part a, e, b, whilst at c it barely assumes a red one.

The cause of this phenomenon is as follows:-The small interstices of the wick, like other porous bodies, imbibe the melted tallow or wax, which is a combination of carbon, hydrogen, and oxygen; these by heat are converted into an empyreumatic oiltwo of the compounds of carbon and hydrogen, carbide of hydrogen and olefiant gas, and carbonic oxide, which burn and produce flame. The external part a, e, b is the hottest, because it is in contact with the atmospheric air which supplies oxygen. The small blue margin is produced from combustion of carbonic oxide and a trifling proportion of carbide of hydrogen. The inner dark cone is filled with combustibles which are only partially consumed, on account of the air which passes through the flame being deprived of its oxygen by a, e, b.

Of the four different parts of the flame, three are as easily perceived in the flame of a lamp as in the flame of a candle; but the last a, e, b, if at all seen in the flame of the latter, must be very indistinct, as it only disperses a small quantity of light.

The following are the three parts necessary for researches with the Blowpipe-the blue, a, b; the one which produces much light, d; and the outer, a, e, b. As the first and second are the most essential, they will be described at length.

THE OXIDATION FLAME.

When an operator with the Blowpipe blows lengthways on the

Fig. 6.

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flame of a lamp, so that the air just passes over the wick, Fig. 6, a long narrow blue flame will be formed,-which is the same as a b, Fig. 5, excepting in shape ;-the flame of Fig. 6 is conical, that of Fig. 5 oval. The heat is greatest at the

extremity of this flame, because it is there the largest quantity of air sent through the Blowpipe is consumed.

In the free flame, the warmest part forms a girdle round the whole, the heat being most intense at f. Where the heat is greatest, substances which are not acted upon by an ordinary flame, oxidate, melt, and evaporate. The further the matter can be kept from the apex of the blue flame, in a temperature sufficiently high, is favorable to oxidation, because the atmospheric air will have free access. The operator must not blow too strongly, as it would be very deleterious to oxidation, especially if the assay rests on charcoal. The wick must be evenly cut, and kept free from all fibres, otherwise yellow streaks, which have a reducing effect, will be mixed with the blue flame. If these directions be adhered to no difficulty can be found in ascertaining how far the tube should be introduced to produce the oxidating flame. It will be found most serviceable, not to have the opening too small in the point of the Blowpipe.

THE REDUCTION FLAME.

By allowing a stream of air to pass over the wick, at a greater distance than in the production of the oxidating flame, the whole ignited mass receives the same direction, and appears as a long narrow luminous cylinder, the end being surrounded by that part of the flame which emits only a small degree of light. By forcing the air as described, the particles rising from the wick, which are perceptible in a free flame, are consumed, and the heat becomes concentrated in a less space. If such a flame be directed upon a metallic oxide, so that the point covers it totally, the oxygen will be eliminated, either partially or entirely, according to the stability of the compound, or the materials upon which it is exposed,— charcoal, or platinum wire.

If the reduction of a peroxide into a protoxide be attempted on a platinum wire, it will succeed, completely, only when the assay is surrounded with the luminous part of the flame: this effect can also be produced in the blue part of the flame, with easily reducible metallic oxides, if the accession of atmospheric air be prevented,

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