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handle, you place it, covered as it is, in the furnace, behind, in a corner until it bas become quite cold. Then opening it you take out the enamel and will wash it, and will again fill it and melt as before, and you do thus until, melted equally everywhere, it has become full. In this manner you compose the remaining pieces."

This would be a very useful and effective apparatus.

In later times however, the regular muffle furnace came into use, which every one knows, consisting simply of a fire clay receptacle which could be filled with coke with a chimney, and in the centre of which a muffle was placed. These muffle furnaces are still made, and are largely used. Excellent furnaces of this class are made by the Battersea Crucible Company of London, whose wares I would recommend to your attention.

The ancients usually employed charcoal. It is a delightful fuel. It is free from sulphur, and very easy to use, and gives great heat. Unfortunately its price renders it prohibitive in England, and I fear we must dismiss it from consideration.

The next fuel is coke. Coke consists of coal that has been highly heatad out of contact with the air. By this the gas and oils contained in the coal are driven off, and also most of the sulphur. The coal is also condensed, and remains in the form of nearly pure carbon. In this form it is called oven coke. Its heating properties are very great, and it produces a beautiful hot, even fire, which, when blown up with an air-blast, produces a very intense glowing heat. The only coke Londoners ever see, is gas coke. This wretched stuff is sold at 18s. a chauldron, and contains little but ash, the best qualities having been already extracted from it. It is almost useless for the purpose of heating a muffle oven.

I next turn to gas. In order that gas may give light, it is necessary that a supply of incandescent matter should be given to it. This may be either in the gas itself or mixed with it, as when the vapour of naphtha is added in the hydro-carbon burner, or else may be in the form of a mantle as in the incandescent burner.

But when the gas is to give heat, then what is really required is a good supply of air; about 10 cubic feet of air is wanted for each cubic foot of gas. In order to get the best results, the air must be thoroughly mixed wtih the gas. This mixing is not at all easy to effect. Air simply put in the same receptacle with gas takes a considerable time to mix.

The commonest method of mixing is in the ordinary Bunsen burner. In this case the gas is supplied through a small orifice

at the bottom of an open tube. As it rushes out in a jet it draws with it a stream of air, which ought to be about ten times its volume. As the gas and air traverse the tube together they become partly mixed. But they do not mix completely. The gas takes more air from the outside of the flame. The mixing is greatly facilitated if the jet of gas rushes violently. A small jet at a high pressure is what is wanted, so as to cause a good whirl of gas and air, and mix them together. This is the reason why a blowpipe is so hot. In that case the air and gas become thoroughly mixed, and a hot flame is the result.

In Fletcher's gas muffle furnaces a short chimney is added to increase the draught of air. If the chimney were too long the draught of air would be too great, and then the flame would be unduly cooled. You want only ten feet of air for each foot of gas and you want them thoroughly mixed. If the flame plays into a corrugated receptacle much good is done in aiding the air and gas to mix, and a hotter flame is the result.

Petroleum is of two sorts, the ordinary lamp oil, and petrol or petroleum spirit. The last of them is used where petroleum vapour is wanted. I would strongly dissuade art workers from the use of petrol in any shape. Its vapour is inflammable and it is very dangerous; besides, in the vicinity of furnaces the reservoir is apt to be heated, and then an explosion or fire may result. All that is wanted can be done with paraffin.

The paraffin lamps most convenient for the art worker are those known as Swedish lamps (see p. 74). This lamp consists of a receptacle A filled three-quarters full of ordinary lamp paraffin. It has an air pump attached to it whereby the air above the paraffin in the space c can be compressed to a pressure of about 80 lbs. per square inch. If the tap be now opened, a stream of petróleum will rush through the pipe and issue in a fine jet from the needlesized orifice at E.

But it is not a stream of petroleum we want, it is a stream of petroleum vapour. Hence, then, the part of the pipe between D and E is well heated by some flame, such as a gas or spirit flame. As soon as it becomes thoroughly hot, then the tap D is gently opened. A litt e petroleum gets through, which is vaporised, and issues in the form of a fine jet of vapour

from the orifice E. It mixes with air as it proceeds, and is lit, forming a blowpipe flame of intense heating power. The vaporiser tube D E is curled round as you see, so that the flame rushes through it, and thus keeps it hot and vaporises the petroleum. Of course, the vaporisation of the petroleum causes a pressure to arise in the tube D E. This is partly relieved by the jet at E; but as it cannot all escape at once at E, the rest presses back on the body of petroleum in the reservoir, and thus the pressure is main. tained, so that only one blow up with the pump keeps the machine running. The real driving pressure is supplied by the heating of the vaporising chamber, the only use of the pressure in the petroleum chamber is to keep a supply of petroleum always ready to run into the vaporising chamber as it is wanted. I call this a very ingenious piece of mechanism. It acts admirably.

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Petroleum, when vaporised at ordinary air pressure, occupies about 500 times its volume when in a liquid state, and requires about 5,000 volumes of air to combust it properly. A gallon of petroleum is therefore the equivalent of about 100 cubic feet of gas.

The efficacy of the flame of blowpipes of all sorts depends not only on the thorough admixture of the gas and air, but on the rapidity with which the flame rushes over the object to be heated. The use of the blowpipe therefore does not increase the total heating power of the flame, it only enables that heat to be concentrated over a small area, by causing a small but rapidly moving flame to take the place of a large slowly moving one. Hence as the object to be heated absorbs heat from the flame, the heat is constantly renewed, and the object, unable to cool the flame round it, rapidly absorbs heat itself.

Alcohol also may be used for heating. Its flame is almost invisible, because it contains

no substance that, by becoming incandescent can give light. When an incandescent substance is supplied its heat is rapidly turned into light.

As in other flames, in order to get a good heat the great difficulty in the case of alcohol is to aerate your flame. All sorts of plans

have been invented for this end. I have here one of the simplest that makes a capital travelling lamp. A little iron pot filled with tubes that admit air to the centre of the flame.

A furnace may be compared to a reservoir. In order to accumulate heat in it rapidly and keep the heat there, you want the heat to get in and not to get out. But an ordinary stove or furnace is a perfect sieve so far as letting out heat is concerned, and it is surprising how much heat the outside of an ordinary stove or furnace will radiate and give away by contact with the air. A long pipe that to the hand seems just hot will heat a whole room, the extent of surface making up for the low temperature. Thus an ordinary muffle furnace, supplied with six or eight large Bunsen burners, radiates away through the sides most of the heat which it receives, and makes the operator very uncomfortable in consequence.

A mere trifle of the heat given out by a kitchen fire goes to roast the meat, probably not per cent., the rest goes in making the face of the cook red and spoiling her temper.

In the course of my endeavours to invent, for the benefit of the jewellery and enamelling world, a furnace that should be economical and therefore comfortable, and be hot where it was wanted to be hot and cool elsewhere, it occurred to me to try whether the process of jacketting, which I had applied with success to household hot water-pipes, could not also be applied to furnaces. The task was not altogether easy, for most non-conductors are fusible in very hot flames.

I will not narrate all the experiments I made. I tried furnaces of every shape, opening in every sort of way, and the results are here before me.

Here I have three furnaces. They are muffles, of 1-inch, 23-inch, and 5-inch width. They are hot within; they are quite cool without. And in consequence they can be heated with extraordinarily small flames. One would hardly believe that the flames I show could keep them hot. The secret is that while the interior is of fire-clay, the exterior is thickly covered with asbestos,

Various sorts of asbestos can be used. The class used for covering boilers does very well, and is made by a number of London makers. The main ingredient is asbestos, made to adhere with a little plaster of Paris and weak glue. Of course, in my furnaces the glue soon goes on the inside, but enough plaster remains to keep it together.

In connection with this subject, I would mention "Uralite." This wonderful material is made in plates which can be screwed or nailed like wood. It is completely fire-proof. A powdered uralite is also sold which, if made up with a little water-glass, holds together very well, and forms an excellent insulator. Furnaces so made can be surrounded with uralite plates, and have a very neat appearance.

In order to apply the same principles to furnaces, I have designed a melting furnace, two of which I have here. They are heated by Swedish burners. Unfortunately, the Swedish lamps make such a noise, that for peace sake I have had to send them out of the room. I will now re-introduce them, and show you them at work. I shall in each case jacket the crucible in a sort of jug with a handle, after which I shall easily be able to pour the metal. The larger furnace contains an alloy of aluminium. [Furnaces here brought in and shown in operation.]

On the table I have put out the requisites for an enameller. I would direct your attention to a little soldering pad and cover, made out of asbestos, and painted with very refractory fire-clay. It radiates the heat well, and with such an apparatus soldering is easy. In fact work can be done that would be quite impossible without some such heat-insulating plates and covers.

It may here be appropriate to say a few words on the subject of fire-clay.

Clay is a silicate of alumina, that is to say, a compound of silicic acid, or flint, with aluminium. Most natural clays contain potash and iron. The result is that when they are strongly beaten the silicate of alumina combines with the potash and forms a small quantity of glass disconnected with the clay. For, of course, as you know, glass is a silicate of potash or soda. Hence the most refractory fire-clays are those that are free from iron and soda and potash. Fire-clays are of this description, and are frequently found in coal measures. Of all of them the best is white porcelain clay, which is a most infusible sort of fire-clay. In some parts of Germany an

extraordinarily infusible sort of porcelain is found and used for chemical apparatus.

In

Common yellow clay, like the lump I hold here, got from my garden, can be made into very fair fire-clay by ridding it of the potash and iron. This is best done by boiling it with some diluted hydrochloric acid. this way anyone can prepare some tolerable fire-clay for his own use. Of course the chloride of iron and potash must be well washed out of it by agitation with water.

I nave here a splendid specimen of natural fire-clay, it contains iron but it is most refractory.

When a new furnace has to be treated with fire-clay, or when any object is made of fire-clay, it is necessary to mix the clay with water, and to knead it most thoroughly so as to get it uniform; it must then be left to dry slowly. Of course the outside dries first, and tends to imprison the water in the damp inside. If considerable heat is then suddenly applied, steam forms inside the mould, that is to say in the body of the clay, and being unable to escape it bursts it.

In order to avoid this, it is necessary to mix something with the clay to keep the pores open. It is of course no use to mix sand. What you want is something that can be burnt out by the heat and leave the body porous. For this purpose pieces of old fireclay are ground up and mixed with the unfired clay. Another plan, simpler for the jeweller, is to mix the fire-clay with some sawdust. A somewhat hard dust is best-box-wood or oak dust is very suitable. In this way little plaques can be made for use in muffle ovens, or muffles can be made if needed. But it is indispensable to dry them gently, and then when dry to put them in a hot oven for some time before they are fired. This will prevent them from cracking.

All fire-clay articles should, before being subjected to a great heat, be warmed up gradually or else there is considerable fear of them flying or cracking.

In making these furnaces it is necessary to have something to bind the material together. Cowhair is not bad. In addition to this I prefer to imbed in the material some pieces of rabbit wire netting which serves greatly to strengthen it.

The process of drying the furnaces must at first be gradual and can be completed in a kitchen oven. Even after this they will still give out moisture for some time, and it is not till they have been some time in use that they

get quite dry, and their non-conducting power is fully developed. The interior lining should not be too thick, for all that is needed is a surface to resist the action of the flame; the rest should be as nonconducting as possible.

DISCUSSION.

Mr. WILLIAM BURTON thought the author had displayed an extraordinary amount of ingenuity by the method in which he had brought his principle of jacketing to bear on small furnaces. Speaking as a potter, he thought the application of the jacketing principle, either with asbestos or similar material, ought to be of the greatest value in his own trade. There was no doubt that of the coal burnt in pottery ovens and kilns in this country about 75 per cent. went to waste in one way or another. The principle of jacketing had, to some extent, already been applied in pottery ovens, and he recently saw in Glasgow, at the works of Messrs. Cochrane and Fleming, the jacketing principle applied to an oven 20 feet in diameter, which he was assured by that firm had saved the coal bill enormously. The principle adopted was of actually sheathing the oven in boiler plate, and in that practical manner a very considerable saving in the fuel had been obtained. He would send Mr. Fleming a copy of the paper, and he would probably carry his idea of jacketing a good deal further by putting inside the sheathing of iron a coating of asbestos.

Prof. W. GoWLAND said he had seen the furnaces at work in Mr. Cunynghame's laboratory, and although the laboratory was an extremely small one, the temperature of the room was never uncomfortable; it hardly rose more than a few degrees after the furnaces had been working for some time. It seemed to him that the application of the author's ingenious and simple principle to the jacketing of muffle furnaces had several very important advantages. In the first place, the jacket protected the operator, which those who had to stand a long time watching the operations would appreciate. It had the addi tional advantage that, for a given muffle, with a given burner, a very much higher temperature could be produced in a jacketed furnace than with the same burner in an unjacketed furnace. Thirdly, in a furnace jacketed in the manner exhibited, there was uniformity of temperature, which was of the utmost importance. In the muffles shown the temperature at the front was the same as at the back. If that principle was applied to assaying metals, for instance, gold or silver, uniform conditions would be obtained throughout the muffle, which were not always obtained with an ordinary furnace. There was a trifling disadvantage connected with silver assaying by the furnace shown, that it would take a long time to cool down, but that could be obviated by working the furnace at just the melting point of silver. There was one assaying

process for which the furnaces would be extremely useful, namely, for scorification, where a higher temperature was required than for ordinary gold and silver assaying. The melting furnaces were extremely good, and just the kind of appliance wanted for certain purposes. It would be agreed that every sculptor ought to have a knowledge of the practical operations by which his model was reproduced in bronze, but hitherto there had been difficulties in the way. Firstly, it had not been convenient for a sculptor to have an ordinary coke furnace built near his studio, and certainly not in it. There was the further disadvantage that in the training of sculptors too little attention was paid to the technical operations of bronze founding. The first difficulty was got over by the apparatus shown. There was no reason whatever why the principle should not be applied to furnaces many times larger than those exhibited, furnaces which could melt 50 or 60 lbs. of bronze, and in that way a furnace would be obtained which any sculptor could have in his studio, and with a little practice he would be able to produce a casting much more satisfactory than any he would receive from an outside founder. In addition to setting up a furnace of that kind in a studio he recommended that the method of cera perduta should be adopted, i.e., the model should be made in wax and coated with clay, the wax melted out and the bronze cast in the clay mould, heated to redness in the same way in which it was done in Japan, and then by the use of a copper-tin-lead alloy the sculptor could reproduce the most delicate touches that he had given to his wax model.

Mr. CYRIL DAVENPORT asked the author if the furnaces could be made much larger, because he thought they must necessarily be small. He also enquired whether there was any great advantage in the gas furnaces shown by Mr. Cunynghame over charcoal, which was generally used.

SIR CLEMENT LE NEVE FOSTER, F.R.S., said that having been born in the vicinity of London, he wished to say a word in defence of London coke, which had received rather harsh treatment from the author. He used 2s. worth of coke a week, which was sufficient to heat his bath water, to heat a radiator, and supply the kitchen and lavatory with hot water, and therefore he thought it was rather unfair to say that London coke was mainly composed of ash. Having at one time had a great deal to do with quantitative blow-pipe assaying, he thought the ideas brought forward by Mr. Cunynghame would be of use to all persons who were engaged in work of that description-they would be able to get their work done more rapidly, and would be able to use larger charges in the little crucibles in which the work was done, and therefore the results of the assays would be more satisfactory. The assaying process also opened up a useful educational path. There were students in many schools who would like to practice assaying

who were unable to do so because of the expense, but by using Mr. Cunynghame's apparatus the student would be able to do assaying in his spare time, and in that way the furnace presented an advantage which had not been alluded to.

Mr. ALEXANDER FISHER thought that anything which made it easier for an artist to realise what he wished than he had hitherto been able to do was a very great advantage. The feature of the furnace which had attracted him most was that it could be placed almost anywhere in the studio, and the absence of heat was also a great convenieuce. He had seen the furnaces at work at Mr. Cunynghame's house, and thought they were altogether admirable.

Mr. M. E. WILSON said he could not say more than thank the author very sincerely for the extraordinary ingenuity by means of which he had achieved his object. The furnace exhibited was exactly what people had been waiting for for years.

Mr. FLETCHER thought Mr. Cunynghame's furnace was the best he had seen during an experience of 25 years. The author deserved the thanks of all workers in metals or art works. One of the great disadvantages of gas furnaces was that many of them required a blast or else a very large chimney and a large supply of gas, which Mr. Cunynghame had reduced to the minimum. He would like to know whether there was any special formation of the roof for the furnace in relation to the muffle. He noticed that the flame had two outlets, and from his experience in experimenting with various gas furnaces of that character he found considerable difficulty owing to the shape of the roof, the distance between the roof and the furnace, and the outside of the muffle. The formation of the roof in the furnace shown was a very great advantage.

The CHAIRMAN wished to join with Sir Clement Le Neve Foster in the defence of gas-coke, but not entirely, because in a furnace it was an abomination; but if gas-coke was used for the purpose which Sir Clement had used it, for producing moderate temperatures in which the ash did not melt but could be raked out, then it was a very handy and convenient fuel. Engine coke, of course, was practically unknown to the ordinary householder. Another fuel not mentioned by Mr. Cunynghame was anthracite. In the old days, in Dr. Percy's laboratory, anthracite was used where the highest temperatures had to be obtained, temperatures capable of melting wrought iron. Anthracite was the most beautiful and perfect of all fuels in the furnace, but it could not be burnt in a furnace the size of a tumbler. A moderate-sized furnace was required and anthracite, being almost pure carbon, and wonderfully free from ash, was, as a fuel, quite unequalled among solid fuels. The author had referred to the mixing of air and gas, Anybody was apt to believe

when they first used a Bunsen burner, or other apparatus of the kind, that if gas and air were fed side by side into a tube, they became perfectly mixed. Imperfect mixing of gas and air not only gave rise to the imperfect Bunsen flame, but also gave trouble in the explosion engine of the motor bicycle and motor car; and he understood some people, who were not content with the motor bicycle as it was at present, had introduced an extra bend in the gas and air supply of the engine, so that the mixture should pass through a longer distance in order to get a more intimate atomic relationship between the fuel and the air, so that when the spark was lighted there was a true instantaneous combustion passing through the whole region of the cylinder. He quite agreed with the author's remarks as to the unnecessary danger of using petrol for the purposes mentioned. Petrol was not so good a fuel as one of the higher homologues, and was quite unnecessary in view of the invention of the Swedish lamp, which enabled one to use common lamp oil petroleum without trouble, and melt metals on a small scale. It had also the advantage that petroleum was a fuel, the whole of which was good fuel, which could not be said of coal gas, or other commercial fuels, and it was also practically free from sulphur. He objected to the use of alcohol, although for domestic purposes it had the advantage that when it was lighted and put out two or three times it did not stink the place out as a Swedish lamp did, if by any misfortune the flame was blown out and could not be quickly lighted again. With regard to the author's design of furnace, he thought the whole essence of the construction depended on the proper use of nonconductivity, the use of materials that did not crack, and the grading of the qualities of the materials, from the hot zone on the inside to the cool zone on the outside. One material all through was not correct. Those who had hitherto been content to make a fire-clay furnace were met with the trouble that if it was made thick and heavy with the idea of preventing too much loss of heat, it required the most tender use to prevent it from cracking; whereas if it was made thin the heat passed through it like a sieve, and terrible variations of temperature must necessarily result on the inside where fuel was very furiously burnt to waste. The beautiful uniformity of heat obtained by Mr. Cunynghame in his furnace was quite out of the question where a furious blast was blown into the furnace, and most of the heat poured away through its thin conducting walls. He was astonished that such principles, which were well known to everyone, had not been hitherto applied by the trade which supplied furnaces to the public, he fancied mainly on the ground that the furnace shown was too big and was not a saleable article. The manufacturer looked upon the public as fair game to exploit; he made such articles as he could easily sell at a good profit, and did not make

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