The Sun.
London, England, 1853-03-26 00:00:00

INSTITUTION- CF CIVIL ENGINEERS.

MARCH 15 AND 22.—Robert Stephenson, Esq., M.P.,
vice-president, in the chair. Both evenings were entirely
devoted to the discussion of Mr. D. K. Clark's paper
"On Locomotive Boilers." The proceedings were com-
menced by an explanation of the diagrams exhibited, and
by reference to examples from the experience of Pam-
bour, and other experimentalists, in corroboration of the
views propounded in the paper. The author's deduc-
tions were admitted as to the practical identity of fire-
box and tube surface, for evaporating action, and as to
the constancy of the evaporative efficiency of fuel ;
whether by radiant or communicated heat, or both toge-
ther, or whether the draught was mild or strong. It
was considered that heat was specific and certain in its
effects. Such expedients as " mid-feathers," &c., which
were resorted to for specially increasing the fire-box sur-
face, were condemned, as they were considered to be no
better than tubes, whilst practically they were incon-
venient and costly ; as, among other reasons, plates of
7-16ths or 4 an inch in thickness were employed to do
the work of the tubes, which were less than ith of an
inch in thickness. A:practical rule, followed by some
engineers, and stated to be founded on extensive
experience, was to allow five feet of heating surface
for 1 foot of water evaporated per hour, and 100 feet
of evaporating surface per square foot of grate. Those
results were found to agree with the maximum rates re-
commended in the paper. It was also argued that the
intensity of combustion materially affected the amount of
heating surface n ecessary for economical evaporation, being
less as the intensity was greater. It was, on the other
hand contended that the formula, as stated in the paper,
would not apply to all engines, and the table of actual
results was given, showing the performance of various
engines, several of which exhibited a greater and others
a less evaporation of water, and consumption of coke,
per square foot of grate surface per hour, than the for-
mula would have given. It was further argued that,
from various causes, no formula could be framed to be of
service, unless all the circumstances, in each case, were
properly taken into account. As an example of the ob-
jections to long tubes, the results were given of the work
done by a luggage engine, on the London and North-
WeStern Railway, before and after alteration. That
engine originally had tubes 14 feet long, with a total
surface of upwards of 800 feet ; the length of the tubes
was diminished to 4 feet 9 inches, and the total surface
was reduced to about 500 feet, when it was found, that
a saving in fuel of 40 per cent. per ton per mile moved,
was produced, with a saving of 23 per cent. per mile
run ; the coke used, per ton per mile, with long tubes,
before alteration, being '5041b., and with the short tubes
.2981 b. The back pressure was contended to be a
serious drawback to the long tube engine, and an ex-
ample was given of a trial of a single engine, on the new
plan, against two of the ordinary kind, with a load of
170 tons, in both cases, and although the single engine
was 43 per cent. less powerful than the two engines put
together, and had2o per cent, less heating surface, yet
it had performed the same distance of 111 miles, in ten
minutes less time, and with 31b. per mile less fuel. This,
it was argued, was owing to the engine exerting a greater
dynamic force by being relieved from the back pressure
of the blast pipe, which in the case of the other two
was applied to force the fire, and to draw the heated
air through the long tubes. By the moffe of placing
the tube plate some distance within the cylindrical part
of the boiler, the tubes were not liable to be choked
with cinders, or the draught to be obstructed. This plan
also afforded an opportunity of reducing the size of
the tubes from 11 inch diameter to 1/ inch, giving, in
the same boiler, an equal area of flue passage, whilst, at
the same time, the proportion of tube heating surface
was increased 34 per cent. per foot of length of tube,
and a very large addition of flame surface was gained.
It was further argued, that although the evaporation of
water per lb. of fuel was the test of the boiler, yet, up
to this time, few, if any, experiments could be implicitly
relied upon, owing to the quantities being estimated by
measurement, instead of by weight, and without due
regard to the variation of the temperature of the water
in the tender. As to the evaporative powers of marine
boilers, as compared with that of the best locomotive
boilers, if an investigation was instituted, it would be
found, that the general features of the best tubular marine
boilers, now used in ocean navigation, were nearly iden-
tical with those of locomotive boilers, but the circum-
stances under which they were used were very different.
In the marine boilers, coal was used instead of coke, and
the natural draught of the chimney, instead of the urging
of the blast-pipe, in a locomotive; salt water was also
used, instead of fresh, and a pressure of about 121bs. or
141b5., instead of from 60 lbs. to 80 lbs. on the square
inch. Although lightness and compactness were im-
portant properties in marine boilers, they were less so
than in locomotives, and the former were frequently
worked for many weeks or months consecutively, with-
out the means of stopping for any extensive repair, or
even to be cleaned except at long intervals. Under
these circumstances, marine boilers required to be worked
less intensely, and the water and flue spaces must of ne-
cessity be larger, to prevent their being choked up. The
following statement showed the comparative proportions
and effect of the two descriptions of boilers :
In the Locomotive Boiler. In the Marine Boilers.
1 square foot of firegrate con- 1 square foot of firegrate con-
sumed about 1121bs. of coke sumed about 201bs. of coal
per hour. per hour.
1 square foot of firegrate re- 1 square foot of firegrate re-
quired about 85 square feet quired about 30 square feet of
of firebox and tube surface. fire-place and tube surface.
1 square foot of firegrate with 1 square foot of firegrate with
the above surface, would the above surface would
evaporate I,ooBlbs. of water evaporate 1701bs. of water
per hour. per hour.
1 square foot of flue surface 1 square foot of flue surface
would evaporate 11.71b5. of would evaporate 5.661b5. of
water per hour. water per hour.
Ilb. of coke would evaporate 1 lb. of coal would evaporate
91bs. of water. 8.51b5. of water.
IH.P. of 33,0001b5. lifted 1 IH. P. of 33,0001b5. lifted 1
foot high per minute, re- foot high per minute, re-
quired about 4lbs. of coke quired about 4.251b5. of
per hour. coal per hour.
From this statement it appeared that, although the pro-
portion between the fire grate and the flue surfaces was
widely different, the quantity of water evaporated, and
the power obtained, by the consumption of a given
weight of fuel, were nearly the same, when allowance
was made for the difference in the evaporative power of
coal and coke. After explaining the table of working
results, &c., it was contended that in no case did the
formula accord entirely with the practical results re-
corded in the table ; the nearest approximation being
that of the Rocket. It had been found in the altered
goods-engine, that certain practical inconveniences arose
from the horizontal transverse water tubes, and two or
three mid-feathers had now been substiuted for' them.
It had been found that intense combustion was
liable to cause the formation of clinkers in the small
fire-box, but which did not occur in the new engine.
When the drivers first took out the new engine,
being unaccustomed to its peculiar action, they kept
thin fires, and drew too much air through the
fuel, which was wasted, by raising steam too freely ;
latterly the fires had been kept thicker, and the
combustion had been slower, whilst the supply of steam
had been fully equal to all demands upon the engine,
which, it should be recollected, had been built expressly
for conveying heavy loads at high speeds, and whose
performances, under these circumstances, were con-
tended to have been among the best recorded results of
the present day. To set at rest all questions as to duty
performed, it was proposed to institute a set of experi-
ments, or trials, with certain loads at given speeds ; the
tests to be "consumption of coke per ton per mile, and
time of performance." The results to be communicated
to the institution. The possible maximum evaporative
power of 11b. of carbon was deduced from the results of
chemical experiments, showing that 11b. of carbon, con-
verted into carbonic acid, developed 14,000 units of heat,
or would raise 14,0001b5. of water through I°, which was
equivalent to the conversion of 121bs. of water at 60°, into
steam of 1201bs. The formula was shown to be derived
directly from the tabulated results ; it was a mere em-
bodiment of results, and represented no theory. It was
explained that the formula referred to the economical
evaporative power of boilers, and that it was in no way
designed to limit the unconditional evaporative power ;
that a boiler might raise less or more steam than the
quantity assigned by the formula, but in the latter case
only by a partial sacrifice of the fuel. In the compara-
tive trials of the Crewe engines and the new engines with
enlarged fire-box, it was shown that, looking simply to
the boilers, the Crewe boilers raised a greater total quan-
tity of water per hour, and more water, per foot of grate,
per hour than the new boiler, with greater economy, in
the ratio of 81 lbs. per hour of coke by the Crewe boiler
to 7/ lbs. by the new boiler. It was explained, with re-
spect to the greater time lost by the Crewe engines on
the trial, that the defect lay, not in the boilers, but in,
the exposed position and unprotected state of the cylin-
ders, by which steam was condensed, and in the too
large size of the chimneys, which should have been only
12 inches instead of 15 inches diameter, and in the blast
pipe, which was carried too far into the chimney.
The formula, being applied to the new boiler, indicated
that it could not economically evaporate above 120
cubic feet of water per hour; and the correctness of this
indication was confirmed by the result of eighteen expe-
riments by Mr. Marshall, as they showed that, though
150 feet of water per hour had been evaporated, it was
at a sacrifice of one-fourth of the fuel, as only nibs.
were evaporated per pound of coke. With respect to the
rapidity with which the new form of boiler could get up
the steam, and which was attributed to the free draught,
it was shown that the Rocket, the first tube-boiler en-
gine ever made, got up the steam in less time than the
new boiler. The benefit of the removal of the tube-ends
it; the new boiler, from the direct action of the fire, was
considered to be more than balanced by the liability of
the lower part of the combustion-chamber to become
over-heated and to be burned away, owing to the lodging
of steam, at the junction with the fire-box. It was
suggested that, in order to obtain results from the new
esennclugiutmeannberdee,erfdteohe combustion-chamber should be abolished, the
eft theto otfh tubesarea.
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statement of "actual working results, &c., "the formula had
ibneetnhemtiwsuoncereerw,iteeod and wrongly applied ; for instance,
engines, of identical proportions, the re-
sults of the formula were stated as 861, 84.4, and 73.7,
whereas the same re
ginseolught to have been applied to
similar 6 discrepancy was ap-
-11 5 and 1021. In the ex-
each. In No. 291 en
'A.here were several unexplained
ppeariremnte,nttshethreesmusletslvebseint
anomalies, and in some instances the engines, instead
of
working at their full power, were performing very i n
adequate duty, and therefor under circumstances to
which the formula was not intended to apply. In the
case of the altered goo
state ds ethngeineen, No. 125, it was urged
that in its originalengine must have been
either in a very inefficient condition, or that its duty
must have been chiefly confined to piloting, when it
would have been consuming the fuel, without producing
any useful effect; as a consumption of 51 lbs. or 58 lbs.
of all
per mile run, with an average train of 115 tons, was out
alteration— .
proportion,lia a Thcansatumtheplar.esonultofof3t9hiebaw.oarkinango1 bs.
working, after