unless the flame was considerable, there would not be sufficient for the steam of air to act upon, for this reason the wick is opened, as shewn in Fig. 4, that it may expose the larger surface, and produce the greatest flame : the stream of air from the pipe should be directed through the channel or opening between the wick, so as to produce a cone the most perfect and brilliant. On examining this cone of flame, it appears to be formed of two different colours, the part nearest to the lamp being of a yellowish white, and that beyond of blue or purple colour.

The subject which is to heated is held in the flame at the termination of the yellowish-white flame, where it receives the greatest heat, and is not discoloured by the soot, which accompanies the white flame.

Glass tubes are, when applied to this flame, quickly rendered pliable, and may be bent or drawn out into threads or points, and hermetically sealed; or, by blowing into the other end of the tube, it may be expanded into a small globe, so as to form various small articles at the pleasure of the operator.

In chemistry, mineralogy, and the arts, the blow-pipe is an extremely useful instrument, being capable of throwing such a powerful heat on a small object, as would be difficult to obtain on a larger quantity of the same substance, in the most powerful furnaces and with this advantage, that the process is always under the inspection of the operator; whereas he can only conjecture what passes in the centre of a furnace.

In using the blow-pipe for experiment, a piece of charcoal is generally used to support the subject, and held in the flame of the lamp; the charcoal should be of a close compact grain, and properly burnt; for if it is too

little carbonised it will flame like a piece of wood, and obscure the object; and if it is too much burnt, it is so quickly consumed, and burnt to ashes, that the object is in danger of being lost in it; the charcoal greatly increases the heat by reverberating the flame, and by heating the object at the opposite side; itself being converted into fuel, and excited by the blast, and thus creates an atmosphere of flame and heated air around it, which prevents the heat being carried off so fast, or the object being so much cooled, as if it should for an instant be moved out of the cone of the flame, from the unsteadiness of the hand, or from accidental currents of air, which would disturb the flame, and cause such a wavering in the point of the cone as to divert it in some measure from the object. In order to prevent more tallow than is necessary from being consumed, to produce the intended effect, it is convenient to have several lamps, with wicks of different thicknesses, viz. one to hold two flat cottons, (such as are used for the Liverpool lamps,) of about one inch and a quarter broad, another to hold four, and a third to hold six, or as much common wick yarn as is equal to those wicks in bulk; glass jets should also be provided of different sized apertures, to suit the greater or lesser sized wicks and flames, and deliver streams of air upon them proportionately, and their jets should point upwards in a small degree: hogslard is also equal, or perhaps superior, to tallow for the lamp.

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On the Construction of the Flues of Hot-houses.
In a Letter from C. LORIMER, Esq. to Dr. DUNCAN.

From the TRANSACTIONS of the CALEDONIAN
HORTICULTURAL SOCIETY.

MR. Burnet, of Viewfield, (a particular friend of mine,)

was the inventor of can-flues. He built a hot-house for vines about four years ago, thirty-five feet long by thirteen feet wide, (inside measure,) with one furnace, which he finds fully sufficient to keep up a proper temperature in the coldest weather. He then consulted me respecting his plan for the flues, and the only credit I can take in the business, was my giving him my decided opinion, that it would completely answer his most sanguine expectations. He followed my advice at the time, and he has since had the largest crops of grapes I ever saw upon vines of the same age; and for the two last years every part of his house, from the bottom to the top, has been loaded with a profusion of fine clusters, so thick, that they appeared every where almost touching one another. From the observations he has made, he informs me, that after the eyes of his vines are all fairly broke in the Spring, and he was at liberty to increase the heat in the hot-house, he commonly found the thermometer, at eight or nine o'clock in the evening, to stand from 72° to 75°. The fire was then mended for the night; and the succeeding morning (about six o'clock) the thermometer kept up within two, or at most three degrees of what it was the night before. His furnace is built after Mr. Nicol's plan, with Rumford-doors; and when the fire is mended for the night he shuts his ash-pit-door quite close, which prevents the heat being too much increased, and occasions a very small consumption of fuel; yet, from VOL. XXV.-SECOND SERIES. 00

the