204 
z in. only—immediately below the surface, and no 
heat is developed in any other part of the apparatus. 
Kindly observe that while the front of the diaphragm 
is intensely hot, the back of the apparatus is so cold 
that I can lay my hand on it. Secondly, the combus- 
tion of the gas, although confined within such narrow 
limits, is perfect, for when once the relative propor- 
tions of gas and air have been properly adjusted, no 
trace of unburnt gas escapes from the surface. 
Thirdly, the temperature at the surface of the dia- 
phragm can be instantly varied at will by merely 
altering the rate of feeding of the gaseous mixture; 
there is practically no lag in the temperature response, 
a circumstance of great importance in operations 
where a fine regulation of heat is required. Fourthly, 
a plane diaphragm such as this may be used in any 
position, i.e. at any desired angle between the hori- 
zontal and vertical planes. Fifthly, the diaphragm 
method is amenable to a variety of combustible gases 
—coal or coke oven gas (either undiluted or admixed 
with water gas), natural gas, petrol-air gas, car- 
buretted water gas are all well suited in. cases where 
unimpeded radiation is required. Finally, the incan- 
descence in no way depends upon the external atmo- 
sphere. When once the diaphragm has become incan- 
descent, and the proportions of air and gas supplied 
in the mixing chamber at the back have been properly 
adjusted, the surface will maintain its incandescence 
unimpaired, even in an atmosphere of carbon dioxide. 
I need scarcely point out to you the many obvious 
purposes, domestic and industrial, to which “ dia- 
phragm heating”? may be applied. In the domestic 
line the boiling of water, grilling, roasting, and toast- 
ing are at once suggested, and although the best exist- 
ing types of gas fires are thoroughly hygienic and 
efficient, I think that the diaphragm may come in for 
the heating of apartments; at any rate experiments 
are being carried out in that direction, 
Incandescent Surface Combustion in a Bed of Refrac- 
tory Granular Material. 
The second process is applicable to all kinds of 
gaseous or vapourised fuels; it consists essentially in 
injecting, through a suitable orifice at a speed greater 
than the velocity of back-firing, an explosive mixture 
of gas (or vapour) and air in their combining propor- 
tions into a bed of incandescent granular refractory 
material which is disposed around or in proximity to 
the body to be heated (Fig. 2). 
This process is capable of adaptation to all kinds 
of furnace operations, as, for example, to the heating 
of crucibles, muffles, retorts, and to annealing and 
forging furnaces generally. Moreover, it is not essen- 
tial that the bed of refractory material should be very 
deep; indeed a quite shallow bed suffices to complete 
the combustion. Neither is it necessary that the bed 
shall be disposed around the vessel or chamber to be 
heated; for if contact with the burnt products is not 
objectionable, a shallow bed may be arranged within 
the heating chamber itself; or the refractory material 
may be equally well packed into tubes, or the like, 
traversing the substance or medium to be _ heated. 
The last-named modification is, as we shall see later, 
specially important in relation to steam-raising in 
multitubular boilers. 
By means of this process much higher temperatures 
are attainable with a given gas than by the ordinary 
methods of flame combustion without a regenerative 
system, and, as a matter of fact, we have found that 
with any gas of high calorific intensity (such as coal 
gas, water gas, or natural gas) the upper practicable 
temperature limit is determined by the refractoriness 
of the material composing the chamber to be heated 
(i.e. the muffle or crucible) rather than by the pos- 
sibilities of the actual combustion itself. When I tell 
NOD 23218) VOLMO2| 
NATURE 
[APRIL 23, I9E4 
you that in a crucible fired by coal gas on this system 
we have melted Seger-cone No. 39, which according 
to the latest determination of the German Reichsan- 
stahlt melts at 1880° C. (3416° F.), and also that we 
can easily melt platinum, you will appreciate the pos- 
sibilities of the method in regard to high temperatures 
with gas-fired furnaces. 
Surface Combustion as Applied to Steam Raising. 
I now come to an important application of the new 
process to the raising of steam in multitubular boilers; 
not that the application of surface combustion is 
limited to boilers of the multitubular type, but because 
our investigations have so far been ptincipally made 
with these. 
Our first experiments in Leeds were made with a 
single steel tube 3 ft. in length and 3 in. in diameter, 
packed with fragments of granular refractory mate- 
rial, meshed to a proper size, and fitted at one end 
with a fire-clay plug, through which was bored a circu- 
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lar hole, $ in. in diameter, for the admission of the 
explosive mixture of gas and air at a speed greater 
than that of back-firing. The tube was fitted into an 
open trough, in which water could be evaporated at 
atmospheric pressure. 
Such a tube may be appropriately termed the funda- 
mental unit of our boiler system, because boilers of 
almost any size may be constructed merely by multiply- 
ing the single tube, and as each tube is, so to speak, 
an independent fire or unit, the efficiency of the whole 
is that of the single tube, or, in other words, the 
efficiency of the whole boiler is independent of the 
number of tubes fired. 
Experimenting with such a tube, it was found pos- 
sible to turn completely a mixture of 100 cu. ft. of 
coal gas plus 550 cu. ft. of air an hour, and to 
evaporate about 100 lb. of water from and at 100° C. 
(212° F.) an hour (20 to 22 Ib. per sq. ft. of heating 
surface), the products leaving the further end of the 
tube at practically 200° C. This meant the trans- 
mission to the water of 88 per cent. of the net heat 
