silk-like fabric can be obtained from it, and that if still further prepared so as to improve its absorbent powers, ramie mantles could be made with a life considerably greater than those of the cotton fabric. It seemed that this was a likely material to work upon in finding a cheap competitor in length of endurance to the collodion mantle, and a success has now been achieved in this direction which I think will play as important a part in the future of incandescent lighting as any improvement that has taken place.

Starting with ramie fibre, and treating it in such a way as to remove all the objections which at first militated against its use for mantle making, and then making it into threads with the least possible amount of twist, Herr Buhlmann, of Berlin, has at length succeeded in making a mantle fabric superior in every way to that given by cotton. As is well known, he has employed ramie for many years in mantle manufacture, but before the later developments in treatment were arrived at, the results were by no means what they should have been, and many of the ordinary Krone" mantles introduced into this country did not show the improvement that was expected of ramie. These last improvements, however, mark a great advance, and Herr Buhlmann has at the same time invented an automatic process of burning and shaping the mantles, the effect of which cannot be overestimated.

In the old method of turning off and shaping a mantle, the impregnated cotton fabric, after drying and shaping on a glass mould, was burnt first by means of a bunsen flame, and was then shaped by a blast blowpipe, this being considered necessary to harden and strengthen the weakly filament. In the few automatic burning machines that have been devised this same lifting and lowering of the mantle over the blast blowpipe was employed, but it is impossible by any such means to get anything like uniformity in the condition of the ash or in the shape of the mantle, and yet Buhlmann has succeeded in getting both in the most simple and effective manner.

Many years ago I attempted to get uniformity in shape by making a burner head of the size and shape of the mantle required of platinum gauze, and by putting the mantle fabric over this tried to burn it down to the required dimensions. I found that there was no trouble in getting it to shrink satisfactorily down to the mould, but there it invariably stuck, and I was fortunate if I got a square inch of mantle off

the platinum head, so I came to the conclusion that it was impossible to do this. However, Buhlmann's superior manipulative skill had led him to a well-deserved success. He makes model in iron wire gauze of triple thickness of the mantle that he requires, and mounts this on a burner tube to which the gas is supplied and into which air under pressure is blasted, giving in effect Mr. Shadbolt's idea of using the air under pressure instead of the gas. The result of this is that over the whole of the iron mould you have that green seething combustion that is such a factor in the inner zo zone of a well-regulated mantle flame, and the gas is burnt so rapidly that what would be the outer zone of an atmospheric burner flame is only a thin almost imperceptible layer above the sea-green sheath. The mantle in its unburnt condition is lowered automatically over this, a lever arm which lowers the mantle also turning on the right proportions of air and gas and starting a small sand glass. The ramie fabric burns away and the whole shrinks down until the green zone is reached, where the strong air blast that is causing this green zone prevents any further shrinkage. In the high temperature of the green zone the ash is baked and hardened for a definite period of time, marked by the running out of the sand. (See Fig. 8, p. 143.)

The burners are made up in batteries of the required number, and are all actuated by the same levers, so that the mantles are all put on, burnt off, and lifted off by the movement of the lever arm. The same action that causes the lifting off also turns off the gas and air blast. Nor is the extra burning needed to harden and strengthen the head neglected, for as soon as the mantle has shrunk to the mould, the lever brings down a ring blast on the crown of the mantle, so that none of the factors of success are omitted.

It will be seen from this description that the iron gauze head of the burner shapes the inner green zone of the flame, and that this in turn shapes the mantle, so that there is no chance of adhesion between the mantle and the mould, as the two never come in contact.

The result of this method of burning is to get a uniformity in size and shape and condition which it would be impossible to attain in any other way, and after having examined and fully tested this method of working the mantles in Berlin, I brought back to England with me two samples out of the number I had seen made. The asbestos loop of one unfortunately got fractured in travelling, but the other I was

enabled to test for endurance and light-giving power. On the ordinary Welsbach "C" burner it gave a candle power at first of little over 60 candles, but to my astonishment, as week after week rolled by, the photometer indicated no decrease in the initial candle power, and for over 3,000 hours, i.e., from May 28th until October 10th, when it was accidentally broken in removing a cracked glass, it continued to give a light of 60 candles for a consumption of 4 cubic feet of gas at a pressure of 12-10ths.

This result is the most extraordinary one I have ever obtained. The tests were taken every ten days or fortnight, and the mantle had to stand the jars and jolts of being taken from the chamber in which it was burning to the photometer and back. Yet through the whole period it led a practically curveless life, and, to all appearance, had it not been for its violent end, might have gone on for a considerably longer period.

The mantle so tested and giving these wonderful results contained a rather higher proportion of the oxides, i.e., the ash was a rather heavier weight, than the mantles in ordinary use for lighting in Berlin, which give a higher initial illuminating value of 80 to 90 candles at the start, and sink to about 72 candles after 600 hours, and then continue with but little loss of light. The result, however, shows that by this system uniformity of light as well as shape can be obtained.

I am inclined to believe that this marvellous increase in life is not altogether brought about by differences in the ramie ash, the conditions of twist in the thread, and the number of fibres present in the thread, but is also largely due to the method of burning.

When an ordinary mantle is being burnt off, as is done by the Welsbach process, it is shaped and seasoned, i.e., blasted in a high pressure blowpipe, and the light emitted is so intense that coloured glass screens have to be used by the girls in the works. I have always felt that this high temperature treatment was a mistake, as it vitrifies the filament and renders it brittle. It also apparently uses up a very large proportion of the light-yielding factor in the mantle.

In the automatic burning of the Buhlmann mantle, however, the fabric is quietly and gently shaped and shrunk down to the mould head that gives it the required size and shape, and in this proportion practically no light is emitted by the oxided filaments. Yet the mantle so produced shows an elasticity and

power of keeping up its illuminating value which I should never have considered possible.

On now examining the ramie fabric, the great differences which exist between it and the cotton fabric are at once apparent, and it will be noticed that it approaches much more nearly to the physical condition of the collodion mantles.

Dr. Killing, who has also used microscopic enlargement as a method for investigating the variations in mantles, has come to the conclusion that the cotton thread consists of about 270 single fibres, whilst the ramie thread made in this way has only about 90 single fibres. The transverse section is therefore much greater with the ramie than with the cotton, and this remains pro rata the same after the impregnated material has been burnt off. In other words, the ramie thread contains only one third the number of fibres that the cotton thread does, but each fibre is three times as thick as that of the cotton, and therefore melts and is destroyed by the heat of the flame less easily than the thinner thread of oxide derived from the cotton fabric. As the fine ash fibres from the cotton fabric fuse more easily together, the lighting power of the mantle made in this way decreases far more rapidly than that yielded by the other type.

On examining the structure of the mantle which had been burnt for over 3,000 hours, and comparing it with the structure of a freshly burnt off mantle, Dr. Killing's view is thoroughly supported, as it will be seen that each fibre remains perfectly separate, and no signs of fusion into a solid mass can be seen.

Whilst inspecting the process of burning off I took the opportunity of calibrating a large number of the mantles present in the dryingroom, and found an absolute uniformity in size and shape. The effect of this cannot be over-rated. It is not difficult to get burners giving a uniform shape to the flame, and with these absolute uniformity of result can be obtained, so that instead of seeing a long street lighted by incandescent mantles, some giving an illuminating value of 100 candles, whilst others are contenting themselves with a modest 25, a uniform effect can be arrived at, and with the length of life that I have indicated, an enormous advance in the position of incandescent lighting would take place.

Another direction in which the future of coal gas will benefit largely, by a cheapening in price owing to economies in manufacture and distribution, will be for use as a fuel. Already the ever-increasing demand made upon the

metropolitan gas companies during the day marks the advance of the utilisation of coal gas for cooking, heating, and power, so that whilst the increase in the amount of gas used at night is only rising by some 3 per cent. annually, the day consumption shows an increase of 16 per cent. Directly it becomes possible to reduce the price of the gas to about 2s. a thousand, advance on these lines will become extremely rapid, and the gas companies are naturally doing everything in their power

largely taken over the sale and pushing of gas heating apparatus, it is a duty they owe to themselves and to their customers to take care that only stoves of scientific construction and good efficiency should be supplied. Many of the worst stoves are the most ornate, and for that reason find their way into many homes, as they in the first place appeal to the eye of the housewife, and afterwards to the nose and health of the household, and the result is that a good customer is converted into an enemy of

to foster this development. It is, however, necessary, in order further to popularise gas as a fuel, that everything that can be done should be done to remove any prejudices that exist against heating by gas.

There are many excellent gas stoves on the market, well designed, and giving high heating duty for the gas consumed, but there are also many that, both in their performance and in their effect on the atmosphere, are radically bad. Now that the gas companies have so

gaseous fuel. No gas fires should be sold or let on hire that do not do a large proportion of the heating by radiation, and a gas company that sells a flueless gas stove, save for hall or passage heating, should be prosecuted.

A cubic foot of coal gas on its complete combustion yields 52 cubic feet of carbon dioxide and 130 cubic feet of water vapour, and if you do not mind breathing hot polluted air, highly charged with water vapour, and getting chilled with cold walls, a Bunsen burner stood on

floor is the most effective method of getting the whole of the heat of combustion into the air of the room, and no flueless stove can do more than this. In order to get something to sell, stoves are constructed in which some of the water is condensed, and the public are gravely informed that this removes all deleterious products. But it is impossible to get away from the fact that if healthful heating is to be obtained, it is the solid objects and walls of the room that must be heated, and not the air, and that although some of the heat is lost thereby, a flue to take off all products is an absolute essential.

The gas companies have it in their power to govern the gas stove trade, and unless they choose to take the initiative, it will retard the popularity of heating by gas to a most serious degree. With all stoves in which solid bodies like asbestos are heated by atmospheric burners, a trace of carbon monoxide is always produced, and if there is not a proper flue passing well into the chimney, a headache is added to the other discomforts.

Improvements in gas motors and gas engines are steadily going on, and as soon as the price of coal gas can be reduced sufficiently to attract this class of custom, a wide field will be opened up for it.

few

The development of large gas engines during the last few years gives promise of an entire revolution in our methods of procuring power, and it is highly probable that within a very years the gas engine will make great inroads upon the generation of power by steam. Already gas engines up to 1,500 horse-power have been constructed, whilst engines of over double that power are under construction.

In England, Messrs. Crossley Bros. and other well known makers are producing a very large number of such engines for driving dynamos, whilst it is stated that on the continent Messrs. Horting Bros. have made or have under construction 32 gas engines, with a total of 44,500 horse-power, averaging 1,390 horse-power each engine, and the John Cockerill Company and several German companies follow not far behind.

With such a development of gas for motor purposes, it is manifestly the policy of the gas companies to make a determined bid for so wide a field of output, and if they can supply a clean heating gas with 460 to 500 B.T.U.'s heating power, it is clear that the convenience of doing away with separate generating plant would cause a large proportion of this business to fall to their share, if the price of the coal gas could be made to compete with a fuel gas of

only 150 B.T.U.'s, that is to say, if nearly the same number of calories could be obtained by its use at the same cost.

Taking the imperfect review of the possibilities of the future and the teachings of the past, what conclusions are we to draw as to the gas of the future? My own opinion is that it will be a 12 candle gas, made by mixing blue water gas with coal gas, the blue water gas being introduced either into the foul main or used as an aid to distillation, so as to do away with any need for enrichment. This gas will have a calorific value of not less than 460 B.T.U.'s nett, and a selling price of not more than 2s. a thousand, the economies necessary to reach this lower price being brought about by making the gas in the holder at 9d. to 94d. a thousand, and distributing at a considerably increased pressure, the pressure being regulated down to 1 inches at the entrance to the consumer's meter.

Gas fittings should be entirely taken over by the gas companies; who should supply incandescent fittings and mantles, and keep them in order at a small yearly rental; and where swinging brackets and other causes demand flat flame burners, the companies should fit nipples with broad slits regulated to burn at the lowest possible pressure.

The reduction in price cannot be made at once, but as the cost of production permits, a reduction of price on gas used for fuel and power purposes should be made first in order to expand consumption in that direction, and by levelling the load, to prevent the necessity for the increase of holder accommodation at the same rate as the increase in consumption, whilst the increase in pressure will do the same thing for the mains.

As time passes on the candle power of the gas may be reduced to 10 candles, and the time will be ripe for radical changes in our methods of carbonisation, which will then follow more on the lines of the coke oven illuminating gas plants now being introduced in America.

Correspondence.

THE SOUTH RUSSIAN IRON INDUSTRY. Mr. BENNET H. BROUGH writes:-Having been prevented from attending the meeting, I have read Mr. A. P. Head's exhaustive paper in the Journal with very great interest and profit. The growth of the South Russian iron trade has undoubtedly been