1020 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[June 21, 1873. 
and clear examination of any particular invention ought 
to be regarded as exceedingly valuable testimony. 
The following are some of the more important points 
brought out by the examination of the above described 
process by Messrs. Keates and Odling. The experiments 
conducted by these gentlemen were made upon two scales, 
the first a manufacturing one, in which the process was in 
use for the manufacture of gas for the public consumption; 
and the second upon a much smaller one, in which, how¬ 
ever, the various apparatus was necessarily under more 
perfect control, and hence some points were capable of 
clearer elucidation. The highest yield of gas obtained 
directly from the coal was 9775 cubic feet, the tempera¬ 
ture of distillation being between 1300° and 1400° F. 
The quantity of oil and tar obtained from one ton of coal 
varied considerably with the nature of the coal used; thus, 
Silkstone coal gave 16 - 4 gallons of tar and oil per ton, Clay 
Cross Main 11-9 gallons, and Pelaw Main 13-9 gallons, or 
a mean of 14 gallons. The highest yield of gas which was 
obtained by the continued distillation and redistillation 
of the oily tar was 29 cubic feet per gallon. The mean 
lighting power of the gas produced from coal was 23'0 
candles, and of that obtained from the tar 25 - 0 candles. 
The quantity of coke used to maintain the heat in the 
various parts of the apparatus was about 33 per cent, of 
that produced, and in the event of the distillation being 
repeated until complete separation into pitch and vaporiz¬ 
able matters takes place, this amount would be much 
exceeded. It must also be remembered that the time 
occupied in the distillation of the coal is just double that 
allowed when ordinary high heats are employed. The 
most successful experiment as yet made with this process 
has shown that from one ton of coal it is possible to pro¬ 
duce 9500 cubic feet of 23-candle gas by a careful regula¬ 
tion of the temperature, and from 14 gallons of oil (the 
mean produce of one ton of coal) 600 cubic feet of gas of 
an illuminating power equal to 25 candles. Against this 
result must be placed the considerably increased time 
occupied for the distillation, and the increased consump¬ 
tion of fuel. It would appear, therefore, from these figures 
that the second process of distilling the oil is of very little 
practical utility. The expense attending the production 
of an equal quantity of gas of a scarcely less illuminating 
power from coal being far less than that attending the 
distillation of the oil or tar. Indeed the experimenters 
themselves consider that the oil would be more valuable 
as a marketable article than as a material for the manu¬ 
facture of gas. That this process is capable of yielding a 
larger amount of gas of high-illuminating power, and of a 
character as permanent as that of gas ordinarily produced 
from cannel coal, is, without doubt, satisfactorily proved ; 
and the one point for the entertainment of gas engineers 
seems to be the relative simplicity and economy of pro¬ 
ducing coal-gas of a high illuminating power in the ordi¬ 
nary way by the distillation of a rich, and consequently 
more expensive coal, or of the adoption of this process of 
distilling an ordinary gas-coal at a low heat, with a cor¬ 
respondingly longer exposure. 
Another arrangement has been patented which, to some 
extent, embodies the above idea, although with some con¬ 
siderable modifications ; thus the processes of distillation 
and re-distillation are carried on simultaneously. The two 
heated tanks for the heating of the tar and oil of the pre¬ 
vious invention are dispensed with, and heated iron pipes, 
m reality continuations of the retorts, placed parallel with 
them, and heated by the same fire, filled with some porous 
material, such as pumice or coke, are substituted. The 
tar formed, which is not so large in amount as that ob¬ 
tained in the ordinary manner, is thus further decomposed 
by its passage over the large heated surface, and the gas 
so produced helps to increase the ordinary yield. If coke 
be used for the porous material, it speedily becomes con¬ 
verted into a pitchy cinder in appearance, almost identical 
with the charcoal after its exposure in the previous pro¬ 
cess, and forms a very fair fuel for the heating fires. There 
is, however, a difference in this invention, which, although 
not claimed as part of the patent, yet forms an important 
point in it, and this is that a jet of super-heated steam is 
driven into the retort, and brought into contact with the 
heated coal. During the carbonization a portion of this 
steam undergoes decomposition in the presence of the red- 
hot coal; its oxygen uniting with the carbon to form car¬ 
bonic oxide, and its hydrogen being liberated as gas, it 
was expected that this hydrogen would also unite with a 
portion of carbon to form some gaseous hydrocarbon, but 
this is not possible, as the highest temperature attainable 
in a retort of this description would be far too low to 
bring about such a direct union, but an indirect benefit 
may arise from this injection of steam, and that is, that 
the gases formed from the coal may be more quickly re- 
mo\ ed from the heated mass, and being at the same time 
somewhat diluted, the tendency to form more complex 
bodies will be partially destroyed, and, consequently, the 
production of the tar and oil will proportionately cease. 
1 he previous neating of the steam is no doubt necessary 
in order to prevent undue condensation, but its being- 
heated to redness, as mentioned in the specification, would 
I 31 ' 0T ' e a difficult and probably unprofitable operation, and 
would certainly be impossible to accomplish by merely 
bringing it into contact with the heated sides of the retort. 
The result of introducing a jet of steam into the retort 
during the making of gas may be said to have been suc¬ 
cessful to the extent to which it has been tried, but the 
amount so introduced requires very careful regulation. A 
^ er <y full and complete trial was made by a number of 
eminent men some years ago upon a plan very nearly 
allied to^this—viz., that which was known by the name of 
White s. hydrocarbon process,” in which steam was in¬ 
troduced into the retort with the heated coal, and the fol¬ 
lowing points appear to have been satisfactorily proved :— 
!• An increase in the produce of gas from a given 
weight of coal was obtained. 
2. An increase in the illuminating power of the gas 
afforded by a given weight of coal. 
3. The amount of tar and other oily products was con 
siderably diminished. 
It is.a generally accepted fact that the quicker coal be 
carbonized in gas-making, provided it be done effectually, 
the more successful will be the operation. In the ordinary 
process this end is far from being reached, the carboniza¬ 
tion gradually proceeding from the exterior layer of coal 
directly in contact with the heated bed and sides of the 
retort towards the centre and more protected portions ; 
and as a consequence of this, the heavier and more con¬ 
densed, and in some respects more valuable gases, coming 
from the interior part of the fuel, have to pass over the 
more thoroughly carbonized and hotter outer portion, and 
will thus suffer a further decomposition before leaving- the 
retort.. Many plans have at various times been adopted 
to obviate this evil, such as exposing the coal in exceed¬ 
ingly thin layers, or forming the bed of the retort of a 
constantly moving stage, upon which a thin layer of coal 
in small pieces is constantly exposed to a uniform heat. 
Some of these methods have been successful, but have had 
in. most cases to be abandoned on account of greater com¬ 
plication of machinery, and hence greater difficulty in con¬ 
tinuous working. A plan—probably the simplest that 
has yet been introduced—has recently been brought for¬ 
ward, the principle of which is as follows :—The retort in 
this case is set in a vertical position, and through its centre 
re\ olves a broad and somewhat deep screw, put together 
in sections, the thread of which is placed at an angle of 
45°, and which comes nearly into contact with the sides 
of the. retort. Through a hopper at the top, coal is sup¬ 
plied, in pieces of small but regular size ; the inclination 
of the thread of the screw impels these pieces against the 
heated sides, where comparatively rapid carbonization 
takes place, and the rate of revolution of the screw is so 
regulated, that by the time the fuel has arrived at the 
bottom of the retort the process is complete, and coke of 
a somewhat inferior quality is discharged into a suitable 
receptacle. The yield of gas is greater by this means, and 
