March 26, _ 1915.

THE COLLIERY GUARDIAN.

649

while the export position last June had become
undesirable, we had not only lost trade, but had lost it
when sulphate of ammonia was cheap and prices had
fallen to as low as £10 7s. 6d., a drop of about £2 10s.
in the half-year, and it was almost December 1914
before it got back to £11. Is it necessary to reiterate
the urgency of putting the manufacture of sulphate of
ammonia in this country up to, if not in advance of, the
German standards of last year ?

Things to do Now.

All the foregoing are suggestions that can be put in
practice in varying degrees according to the individual
requirements of the sulphate of ammonia manufacturer.
There is no need to dawdle about, shivering at the
bogey of German recurrent competition as soon as the
war is over, because no great amount of capital need be
sunk or will be at stake. The improvement of the
sulphate of ammonia situation calls for no Government
guarantees, subsidies, tariff adjustments, Parliamentary
committees or kindred impedimenta, or even sugar
convention disruptions. It is simply a case of getting
busy right away, all round, fortified by the certain
knowledge that when we have really first-class sulphate

Fig. 1.—Sectional View through

Air Inlet Valves and Plates.

to offer we shall have the right thing to fight future
German competition with, and what is still more
important as well as reassuring, we shall have behind
the right article a most valuable asset in an unalienable
and active goodwill, that must indubitably give a lasting
preference to British sulphate of ammonia in France
(almost a lost market', Spain, Italy, Russia, America,
Belgium, and possibly Japan. Surely we can command
the trade of the other consumers if the quality is right ?

The Outlook.

There is certainly—to put it as mildly as possible—a
sound prospect of a well-supported and increasin g market
for sulphate of ammonia, while there is promise of
prices settling in the region of £14 to £14 10s There
will also be chances to follow up in new or expanding,
markets, but the main object now on the horizon is to
let there be top-notch-best-possible-sulphate of ammonia-
obtainable to offer in all markets, and, above all, let that
sulphate be British sulphate of ammonia.

COAL SHIPPED FROM PORTS IN ENGLAND,
SCOTLAND AND WALES

During February 1915 Compared with the Corresponding
Month of 1914.

The following figures, extracted from the tables
issued by the Commissioners of H.M. Customs and
Excise, show the quantity of coal shipped from the
United Kingdom during February according to groups
of ports:—

Cargo.

	Feb. 1914.	Feb. 1915.
	Tons.	Tons.
Bristol Channel ports 		2,538,805 ..	. 1,762,784
North-western ports 		37,345 ..	32,292
North-eastern ports 		1,857,441 ..	.. 1,122,311
Humber ports 		567,111 .	.. 244,235
Other east coast ports 		30,352 ..	7,594
Other English ports 			10 ..	20
Ports on east coast of Scotland	541,061 ..	214,560
Ports on west coast of Scotland	153,752 ..	..	245,694
Total 		5,725,877 ..	. 3,629,490
Bunker.		
	Feb. 1914.	Feb. 1915.
	Tons.	Tons.
Bristol Channel ports 		383,331 ..	.	400,536
North-western ports		350,232 .	336,718
North-eastern ports 		259,961	210,717
Humber ports 		244,026 .	119,641
Other east coast ports ...		121,807 .	77,865
Other English ports 		63,409 ..	13,931
Ports on east coast of Scotland...	94,965 ..	48,617
Ports on west coast of Scotland...	94,144 .	92,373
Irish ports		3,257 .	685
Total 		1,615,132 .	.. 1,301,083

The Income Tax Reform League report that the Inland
Revenue authorities have made some small concessions in
the income tax. Until recently it has been the custom of
the Inland Revenue authorities in assessing profits for
income tax to refuse to allow any deduction for depreciation
of fixtures and fittings from revenue receipts, but instruc-
tions have been issued to surveyors of taxes stating that
claims of this nature are to be admitted. Another small
concession which has lately been granted is the allowance,
as a deduction from revenue, of the expenses of removal of
a business to new premises.

THE SCOTT AIR COMPRESSOR.

Notwithstanding the increasing use of electricity in
mining work, the demand for efficient air compressors
is one that grows rather than diminishes, and the high-
speed compressor may actually itself be said to be a
product of the electric motor.

In a high revolution air compressor reliable valves are
a sine qua non, otherwise the waste of energy due to
excessive clearance and leakage will become very
pronounced.

The Scott patent air valve is perhaps the main feature
of the Scott air compressors, made by Messrs. Isaac
Storey and Sons, branch of United Bras-sfounders and
Engineers Limited, of the Empress Foundry, Cornbrook,
Manchester. In these compiessors the upper side of
the piston is fitted with a set of air inlet plates and ball
valves—an example of which is shown in fig. 1—the air
to the cylinders being admitted to these valves on the
suction or downstroke. The positive and rapid opening
of the valves is automatically ensured by the inertia of
the balls at the commencement of the suction stroke.
At the end of the compression stroke, when the piston
commences its suction stroke, the rapid movement of the

Fig. 2.—Sectional View of Simple Single-crank
Compressor.

piston causes the inertia of the balls to pull them quickly
off their seats, and thus opens the valves at the precise
moment desired. At the lower end of the stroke, the
momentum of the balls instantly closes the valves
immediately on the commencement of the compression
or up stroke. A very large area through the valve plate
is thus obtained with a lift of about in. only.

The valves are in the form of hardened ground steel
balls of small diameter, each working on a recessed-
drilled seating made from hard steel plates. The
bottom plate, it will be seen, is drilled with a series of
holes of two diameters, the top portion slightly larger
than the ball, and the lower portion smaller in diameter
than the ball. This forms a pocket, in which the ball
works, and a seat for it to rest on. The upper plate is
drilled to the same templet centres as the lower one,
and is then fixed so that the holes in it come half way
over the holes in the lower one, the solid bars between
the holes in the upper plate coming directly over the
centre of the balls in the lower plate, and so forming a
stop for the lift of the valves. Both the delivery and
inlet valves and plates are of similar construction, and
can be easily examined or removed when necessary.

The air-inlet valves are securely bolted to the top of
the trunk piston, and the air is admitted freely from
the underside of inlet valves through the large air
passages provided. The discharge valves and plat's are
secured to the top cover, and can be inspected by simply
removing the top cover. At the same time the inlet
valves can be easily examined thiough the open cylinder
top.

The question of cooling is an important factor in the
working of compressors. In the Scott compressor
cooling efficiency is obtained by the arrangement of
totally immersed air cylinders, which, owing to the fact
that they have no large piston valve or other chambers
cast on, are perfectly cylindrical. The cylinders and
intercoolers are completely surrounded by a steel or
cast-iron tank, through which a large volume of water

is circulated, suitable connections being provided in the
compressor frame or water tank. In two or multi-stage
machines, the air, after being compressed in the low
pressure cylinders, passes through intercoolers to the
high pressure cylinders. These intercoolers consist of
a set of brass tubes expanded into tube plates in the
ordinary way. The air is, however, passed through the
tubes, instead of being passed outside, as usual, while
the intercoolers are immersed in the cooling tank. The
result is that the air is divided up into a number of
small streams, and the formation of air pockets in the
intercoolers is entirely obviated.

The compressors made by the firm may be divided
into two groups, viz., the simple single-stage suction
valveless type foi- belt, rope, or motor drive, and the
steam, motor, or belt driven series intercooling type.
Figs. 2 and 3 show respectively sectional and external
views of a single crank compressor. These small
compressors are made in seven sizes, with free air
capacities ranging from 20 to 300 cubic feet per minute.
Fig. 4 is a cross section through the low pressure
cylinder of a 3-crank series intercooling type compressor
suitable for belt, rope, or motor drive. This type is
specially recommended for compressors of the larger
sizes, owing to its extreme regularity of turning, due to
the correct equalising of the pressure relations in the
three cylinders.

In this machine the two outer or low-pressure cylinders
are used for the first stage, and the central or high-
pressure cylinder for the second stage of compression.
By these means an equal division of power is obtained
between the three cranks. A cooler delivery of air is
also secured in consequence of the exact proportioning

C.H. SCOTTS
PATENT

" 133 •

Fig. 3.—External View of Simple Single-crank
Compressor.

of the compressions between the high and low-pressure
cylinders. The low-pressure air cylinders are fitted
with a set of suction valves and plates at the lower end,
as shown above. In the high-pressure cylinder, how-
ever, these are not fitted, the lower end of the cylinder
being open and in direct communication with the inter-
coolers, from which the air, after being first compressed
in the low-pressure cylinders, is taken and admitted
through the high-pressure piston inlet valves for the
second or final stage of compression. The cross-sectional
view, fig. 4, in addition to representing the construction
of the series intercooling type of compressors, can also
be taken as typical of the general design and construc-
tion of the single crank high efficiency suction valve
type of compressors.

The standard design of two-stage steam-driven inter-
cooling compressor, fig. 5, is arranged with either two
or three cranks at equal angles. In their general
construction and design the air cylinders and valves are
precisely the same as those of the belt or electrically-
driven series type compressors illustrated in fig. 4.

The speed governor and pressure regulator fitted on
all Scott steam-driven series-intercooling compressors,
as shown above, is designed to operate automatically
under wide variations of load. It will be noticed on
referring to fig. 5 that a small copper supply pipe is
fitted from the discharge chamber at the top of the
compressor to the actuating piston of the regulating
apparatus. When the discharge air pressure reaches a
fixed maximum, its action on the top side of the
actuating piston causes it to overcome the weighted
lever, and forces the spindles down, thus closing the
throttle valve and shutting off steam. The automatic
control gear is arranged so that the speed governor
prevents excessive speed, whilst at the same time the
air pressure control is so adjusted that when the
pressure on the actuating piston reaches its maximum
it brings the speed of the engine down to a dead slow
without stopping it, and automatically speeds the
engine up when the air pressure falls again, thus
allowing it to resume its normal work.

The two-crank compressors are made in six different
sizes, with free-air capacities of f:om 300 to 1,000 cubic
feet per minute; the three-crank type are constructed
in seven sizes, the free-air capacities ranging from 600
to 3,000 cubic feet per minute.

Where compressors are to be driven by electric