The Sun.
London, England, 1856-10-14 00:00:00

new feature is the employment of bristles, instead of I
sheepskin, in all the sponges and rammers for the guns;
and a further one is the employment, for boat guns, of
light and elegant wrought iron carriages, of which she
has three—one for a 9-pounder, a second for a 12
pounder, and a third for a 24 pounder.
The engines of the Merrimac are by Mr. Parrott,
of the Cold Springs Foundry, New York. She has
two cylinders 72 inches in diameter, and three teet
stroke. These are placed close to the shaft, on oppo.
site sides of it, leaving room only for the crank.
Each piston has two piston-rods, one above and one be-
low the shaft ; these carry a cross head, from which the
connecting rod reaches back to the crank, as is well un-
derstood by the engineers. Each cylinder has its con-
denser at the side of it, and its air-pump opposite to it.
The air-pump rods go through the cylinder ends direct
to the piston. She is fitted with four of the vertical
tubular boilers, patented by Mr. D. B. Martin, engineer
in chief of the United States navy, similar to those fitted
previously in the Susquehanna, by Merrick and Son, of
Philadelphia. The boilers are of Iron, with brass tubes,
and have the following general dimensions :
Length of each boiler, athwart ships, 11 feet ; breadth,
fore and aft, 14.8 feet ; length of vessel occupied by four
hoilers, 31 feet 8 inches ; breadth of ditto and fire-room,
31 feet. The fire-room is between the two pair of boil
ers, the furnaces firing athwart ships, and the flues de-
livering into one chimney. Height of boilers, 13 feet 6
inches ; cubical space occupied by all the boilers and fire-
room, being the content of a parallelopipedon included
within the above circumscribing lines, 13,240 cubic feet;
number of furnaces in all boilers, 16 ; breadth of ditto,
each, 2 feet 101 inches ; length of ditto, each 7 feet ;
grate surface area, in all, 338 square feet ; number
of tubes in all boilers, 5,480 ; length (or height) 37 in. ;
diameter (outside) of the tubes, 2 inches ; heating surface
in fuinaces and back connections up to tubes, 1,614
square feet ; heating surface in tube boxes, 8,508 square
feet ; heating surface in tube boxes, and connections to
smoke chimney, 1,581 squarefeet ; total heating surface in
all boilers, 11,703 square feet ; proportion of the same to
grate area 34.6 to 1.00 ; flue area or calorimeter between
tubes in all boilers, 42 square feet ; proportion of the
same to grate area, 1 to 8 square feet ; diameter of smoke
chimney, 8 feet.
The boilers all have water-bottoms' with not less than
6 inches of water space at any point ; back of the furnaces
these bottoms rise to the back connections; the tube boxes
are above the furnaces, and rise about 3 inches to the
front end of the boiler, where they enter the front con-
nections. The boilers are of 3.Bth inch, and inch best
American plates, double riveted and caulked inside and
est, throughout, and are well braced. The weight of all
four, when empty, is 25t,0001b. Their total weight, when
filled to the working level, is 440,0001 b.
To test the economical evaporative efficiency of this
form of boiler an experiment was made on the 13th of
March last, in the presence of several engineers of the
navy, the conditions and results of which were, as pub
lished by Mr. Merrick, the maker, as follow :
Two boilers only were used, and the dampers were
nearly closed.
The coal used was anthracite, and of an, inferior qua-
lity. The engines are fitted with Stevens's cut-off, which
was adjusted and permanently fixed to cut off as follows:
Port engine, one end

4.12
ft
Starboard engine, one end
3.35
It
Average per indicator-card, with full throttle 3.97 feet.
Adding to this the average clearance at each
end of the cylinder, and including, also,
the steam passage, &c., between valves and
cylinder, equal to 23.820 cubic inches, or
the area of the cylinder by 6.05 inches of
stroke, or

Average length of cylinder, filled at each
single stroke
Preserving the same level of water in the boilers, and
(as nearly as could be ascertained) the same quantity of
coal in the furhace, or about the same fires, and main-
taining the-same pressure of steam, 4,2001 b. of coal were
consumed, and 1,615 new revolutions made and noted by
register, the duration of the experiment being 3 hours
57 minutes. During this time 11 double cards were taken
on the two engines, which showed a mean pressure of
steam entering the cylinders, during that part of the
stroke over which steam was admitted, of—
Total pressure—Port engine, 18.991 b • starboard en-
gine, 21.811 b, of which (Pambour) the volume is 1257.
Hence the water evaporated during the experiment
was as follows :—the two cylinders being 70 in. dia-
meter =26.41 square feet of area,
26.71 x 4.474 x 1615 x 4 x 62.5
1257 = 39,3721 b of water,
which, being evaporated by 4,200 lb of coal, gave 9,137
lb of water per lb of fuel.
The temperature of the hot well was 89i deg., and of
the feed-water entering the boiler at (probably) 85 deg.
The evaporative power of the boilers will at once be
seen from the above figures of Mr. Merrick. In the
Merrimac very excellent results have also been obtained
with Mr. Martin's boilers. Her coal bunkers carry
about 600 tons of coal. A small pair of donkey engines
are provided on the main deck for coaling, raising heavy
weights on board, &c. These auxiliary engines have a
suitable boiler to supply them when the main boilers
are not at work. The steam pumps are fitted in connec-
tion with the large engines for pumping out the bilge,
extinguishing fires, &c. These steam pumps may be sup•
plied with steam from the auxiliary boiler, if desired.
The Merrimac is fitted with a Griffith's screw propeller,
with means of varying the pitch. In this respect she
differs from her sister ships, all of which have ordinary
propellers. The Niagara is, we understand, to have a
Griffith's.
The propelling arrangements on board the Merrimac
are very complete. The forward thrust is taken by a
series of collars, and the backward thrust by a brass disc
dropped down between the end of the propeller bearing
and the after sternpost. This disc may be readily re-
newed when worn. The shaft is supported between the
engines and the dead wood by bearings and intermediate
sprinr, supports, and a cooling pipe is led from the out-
side of the ship over each. The after-propeller bearings
are of wood, upon Penn's principle. The propeller is raised
by a cable and pulleys, the cable leading to the capstan.
A long wooden stay, tightened by a screw, is used for
keeping the propeller down in its place, and suitable
means are also provided for steadying the propeller dur-
ing the raising of it, for slinging it when raised or parti-
ally raised, &c.

The greatest speed ever attained by the Merrimac
under steami
owingges
ra,
al
to otetnf:tei improvements
attained
wasaetdihne
withds
ee e
defects
ecgnt
sne
er knotsieandtgeh enpoee:r
connectiondbhr board,
b: rode,
driving
lapi
tandha
cut
eat
haohn
erffi
and
rsarslahwrueel
trveihaeastedredaueus:e
mlravmtwehvgas
doaaauel
beivdswnvteee teais
being
steamingulwsn 9mdh
beforeaei
icrl
inches
estvhpphieerheareseeytvdone
fnntifavourablestefihctreemhsrstesusaeft
sruhrhyol
ellkeeaesecn.soo dun
tl circumstances.osdhinmhaoeynns ot tth:economicalsu.
will,
at 15 inches. But radical changes must he made i
&c.—are very well arranged.
The Merrimac is full of evidences that the American
Government are willing to give trial to improvements of
a promising character in their ships of war, notwith-
standing the changes which their introduction renders
necessary. At the same time there are arrangements,
which have been proved highly valuable in our own
service, unadopted by them. For example, instead of
the admirable lightning conductors of Sir W. Snow
.Har-
ris, used with so much advantage by the old bit of
chain long discarded here, lies down against her shrouds,
and gives great offence to the eye of the intelligent visi-
tor. But, on the whole, the useful improvements
out-number the defects. This we might show
greatly
' great length if we thought it desirable. It will, how-
ever,clb be sufficient to add a further fact or two. The fish-
davit is centred on a hoop on the foremast, and may be
swung over either anchor for fishinc, it, and may also be
used to assist in the removal of the heavy berthing
which has to be taken down when the bow pivot
is used. Both operations may be performed by
gun is
steam power derived from the auxiliary engines. An-
other useful arrangement is the use of a hinged tongue-
piece, which may be pressed down between the links of
the cable by a screw when the cable has to be fleeted.
Another is the employment of light bulk-heads around
the engine-room hatches on the main deck. Whether
the absence of all mess tables for the ship's crew is an
improvement or an act of retrogression we leave our
naval officers to decide.
In our next number we shall probably publish a few
further statements respecting the Merrimac. At the same
time we believe that the points of chief importance are
included in the above remarks.
tarTffi
nhntheehdeernere.

The Niagara is built, we are told, as an experiment

and it is perfectly certain that if she should prove a tho:
roughly strong and efficient ship of war, she will surprise
everyone who has hitherto been oonsideeed well informed
on the nature and requirements of war ships. The his-
tory of this ship's origin is simply this :—Mr. Steers, of
New York, built the America yacht, which proved to be
a very fast one. Tiflis gained him reputation and friend,,
and secured him orders for constructing various other'
vessels of larger sizes. He succeeded in building more than
one fast and serviceable commercial steam ship, and when
the American Government resolved upon making
a de-
monstration with large steamships of war, 111rSteers, or
the friends of Mr. Steers, succeeded in getting. the design
and construction of one committed to him, Mr. Steers
knew but little, if anything, practically of ships of war,
and, if we are rightly informed, cared to know but little
of them, except what the light of nature supplied him
with, for we are told he availed himself but very little
of the freedom with which he was permitted to have
access to the bureau of construction and all that it
contained. More than one professional American
gentleman has spoken to us
'° It was but reasonable," ongly epen this point.
Says the United States
Nautical Magazine, "to suppose that ever facility
would be afforded Mr. Steers, now that y
improvement
seemed to bo really intended, and, with the exception of
the propelling power in the
quantity of the canvas, the
ground tackle in the kind ofanchor., and the ventilation,
in the improved side lights I,'
use, he has been allowed t ' -e has thought proper to
0 exercise his own judgment,
both in the mole' and manner of con-truction, and i.,
like the cole.tructor of hio, quite willing to take the
whole measurd of its weight and bulk responsTibility, having a full knowledge
of . e
his vessel, as her dimensions
and calculations will show, is the lareest of the six, and
is also of a very different model and
construction. In
the construction of the Niagara, it is alleged that there
are
the nay
which are of great importance to
the
, which have never been appreciated
in the y either in this country or elsewhere. It was
asulopupe would this
in the model and internal arrangements
. it i this vessel differ from the other five vessels;
nut s discoverable that not only is the form of
.the fabric and her arrangements in armament
different, but that the manner of distributing
the Materials throughout the vessel is also en-
tirel* different, utility being regarded, as o more
col:Pinnace than the tinwhonoured precedents, the eon,
__ , _

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