1872.] Engineering. 105 
round the journal. The box is divided into two chambers by a diaphragm, so 
that, really, we have two fans on the same shaft, and their boxes communicate 
by a hole in the diaphragm around the shaft. The fan at the closed end of 
the box is in’ form and function a blowing-fan. The outer fan is the pul- 
veriser. The coal, fed into the open end of the pulverising chamber, is 
caught by the swiftly revolving paddles, and reduced to powder, and is then 
sucked by the fan through the diaphragm, whence it is expelled by the 
ordinary tangential pipe along with the blast. The coal is fed in the form of 
coarse gravel; it is delivered as fine as flour. The function performed by this 
machine is a double one. It pulverises the fuel, and delivers it, along with 
the blast, into the combustion chamber, by a single and indivisible operation.” 
It has been ascertained from practice that the most suitable velocity for the 
pulveriser is about 10,000 feet per minute for a point on the periphery of the 
paddle, which, for an 18-inch pulveriser, would be about 2100 or 2200 revolu- 
tions per minute. -The feed of fuel must, of course, be determined primarily 
by the requirements of the furnace, and the minimum quantity that will effec 
the desired temperature should, in each case, be determined experimentally. 
The amount of air admitted should be sufficient to float readily the pulverised 
coal, and no more. If excessive, the increased draught through the pulver- 
ising chamber will float out much larger particles than can burn effectively. 
Generally speaking, it is advisable to keep the supply of air quite small. The 
18-inch pulveriser, commonly applied to furnaces, reduces 200 lbs. per hour of 
anthracite coal, the proportions of size being about like the yield of millstones. 
It requires about 3} horses’ power to effect this. The same power reduces 
about 300 lbs. of bituminous coal, a large proportion of it being very fine. 
The entire yield will burn easily, wafted through a hot furnace. A 42-inch 
pulveriser, requiring about 15 horse-power, will deliver 1000 to 1200 lbs. of 
anthracite per hour, 2000 Ibs. of bituminous coal, 2500 to 3000 lbs. of quartz, 
2000 to 2500 lbs. of top cinder, 3500 to 4000 lbs. of limestone, goo lbs. of 
unburnt bone, and 50 bushels of wheat. 
Patent Gas.—It is some time since any radical change has been introduced 
in the manufacture of coal gas. Dr. Eveleigh has recently succeeded, not 
only in manufa@uring a gas purer than is generally obtainable, but he likewise 
converts the residual products into permanent gas in a manner at once 
practical and economical. The process introduced by Dr. Eveleigh consists of 
the distillation of coal in iron retorts, at the comparatively low temperature of 
goo° (Fahrenheit). The hydrocarbon oils go over with the gas, and they are 
carried together to a condenser, where the oily matters are rapidly condensed, 
the gas passing on to its own condenser and purifier. The hydrocarbon oils 
are collected and passed first into a heated pan, where they are re-vapourised, 
the vapours being conducted to a re-distillation retort charged with charcoal, 
and heated to a temperature of about 1200° (Fahrenheit). By passing these 
vapours through charcoal, it is found that they are decomposed and converted 
into a permanent gas, which, however, is of a lower illuminating power than 
that produced directly from the coal. This secondary gas is passed through a 
condenser, from whence it is condu@ed through a receiver containing the pri- 
mary gas with which it is mixed, the union of the two giving a gas of very 
high illuminating power. Dr. Eveleigh’s experience during a long course of 
trials at his works is, that the retorts, the heating pans, and the re-distillation 
cylinders require only two-thirds of the quantity of fuel employed in the 
ordinary process, owing to the superior quality of the coke produced. As 
regards the results of working, he finds that 1 ton of Pelaw Main (Newcastle) 
coal, without the aid of Cannel, produces 11,000 cubit feet of 18-candle gas, 
with only 2 grains of sulphur in any form in roo cubic feet, or about one- 
twentieth of that usually found. By slightly increasing the distilling heat, 
12,000 cubit feet of 17-candle gas can be obtained from the same quantity and 
description of coal as above, but with a slight increase of sulphur, not, how- 
ever, exceeding 5 grains. The yield of oil is found to be twenty gallons per 
ton of coal, and in its re-distillation two valuable produéts are obtained 
in addition to the gas. One is the pitch, which has been assessed at a very 
high market price ; and the other is a drying oil, which is of value for varnishing 
VOL. VIII. (0.S.)—VOL. II. (N.S.) P 
