1136

THE COLLIERY GUARDIAN

December 3, 1915.

CURRENT SCIENCE AND TECHNOLOGY.

Heat Transmission.

Prof. J. E. Petavel, in a paper, read before the
Manchester Association of Engineers, dealt with research
work on heat transmission to determine experimentally
the heat flow under certain definite conditions, and to
estimate the relative importance of the three modes of
transmission, namely, by radiation, conduction, and con-
vection. For the tests made in air at atmospheric pres-
sure, ordinary steam piping was used. A pipe about
7 ft. long was connected to an efficient steam separator
by a short length of copper tubing, and the heat loss was
calculated from the condensed steam collected per
minute. Pipes |, f, 1, 2, and 6 in. were tested at steam
pressures ranging from atmospheric to 200 lb. A
number of experiments were also made with sheet metal
pipes of 3, 5, and 12 in. diameter, with steam at atmo-
spheric pressure. The larger sizes were 14 and 15 ft.
long. Finally, the rates of cooling of some hot-water
tanks, one of which had a capacity of 14,000 gals., were
measured. The resulting values of the heat loss from
metal surfaces, such as bare steam pipes of various
diameters under different temperature conditions, show
that the heat loss from steam-heated surfaces is due
mainly to convection. Taking as example a pipe of 1 in.
external diameter, with emissivity of 3-00 British
thermal units for steam at atmospheric pressure, the
loss by radiation will be 0-45, or, say, 15 per cent. The
loss by conduction in an enclosure 8 in. greater in
diameter than the pipe, works out at 0-13, or about 4 per
cent., and would be rather less in an enclosure of larger
diameter. Convection accounts for 81 per cent, of the
loss from a lin. pipe containing steam at atmospheric
pressure, and a similar reasoning would lead to the con-
clusion that it is about 80 per cent, for steam at 1001b.
pressure. For very small diameters below 0'1 in., con-
duction becomes of relatively greater importance, and
may even amount to one-half the total. The figures
refer to an oxidised surface such as that of the ordinary
unpainted steam piping. Careful polishing would
diminish the amount lost by radiation to one quarter,
whilst machining the pipe to an ordinary finish would
halve the radiation. In the first case the loss from the
pipe containing steam at atmospheric pressure would
decrease to 2*67, and the convection would be 92 per
uni. -I the total. In the second the total loss would
decrease to 2’78, and the convection would be 87 per
- ent, of che total. As an illustration, the 2 in. radiator
used i: the above work lost 2-59 British thermal units
per degree when coated with lamp black, this being
reduced to 2*36 British thermal units after cleaning.

In experiments on the effects produced by insulating
materials, to diminish the loss of heat caused by con-
vection currents, and reduce radiation, it was found
that all solid materials used as insulators are better
conductors than air, and the use of an insulating material
therefore really increased the loss due to conduction. For
instance, in the case of a wire of small diameter in air
at low pressures, conduction is a more important factor
than convection, and an insulating cover will actually
increase the thermal loss. Even with a 1 in. pipe, a
material such as slag wool or asbestos, if applied in a
solid, compressed block, would increase the total loss.
The insulating effect depends on arranging the substance
so that the least quantity of material will subdivide the
space round the pipe into separate air cells as perfectly
as possible. Thus the efficiency of slag wool is at a
maximum when the solid material occupies about one-
fourteenth of the space. Under these conditions, the
loss by conductivity is increased from 0*13 to 0’40, but
the loss by convection is reduced from 3*2 to 0'14, and
the total loss (0-54) is only about one-seventh that of
the bare pipe. When the material is either more closely
or more loosely packed, the total loss increases; in the
former case because of the increased conductivity of the
solid material; in the latter case because of the greater
loss by convection.

Experiments carried out in air at pressures up to
2,5001b. per sq.in., show that, as the pressure rises
from atmospheric to 150 atmospheres, the loss per degree
increases to nine times its original value. This is for a
temperature difference of 152 degs.; at high temperatures
—2,000 degs. Fahr.—radiation forms a large proportion
of the total loss, and hence the increase is relatively
less—five times. At all pressures the heat loss is very-
large for small diameters, but decreases rapidly as the
diameter increases up to Jin., and becomes relatively
constant for diameters above 3 in. For a small
wire ait high temperatures and pressures, the con-
ditions combine to produce a large heat loss. Thus, for
a wire one-twentieth of an inch diameter at 2,000 degs.
Fahr, and 140 atmospheres, the loss is 140,000 British
thermal units per sq. ft. per hour, or 400 times that of
an ordinary steam pipe. The loss reaches a maximum
when high temperatures and pressures are combined
with rapid motion of the gas; in the explosion of gases
fired at high initial pressures, the heat loss per sq. ft. of
cooling surface was found to be 223,000 British thermal
units per hour.

The Size of Collieries in the United States.

Since 1909 the reports on the production of coal 'issued
by the United States Geological Survey have included
statements showing the distribution ' of the output
according to the importance of the producing mines in
the various States. In these statements the mines have
been divided into five classes, those of the first class
including, the mines producing 200,000 short tons or
more during the year; mines of the second class, those
producing from 100,000 .to 200,000 tons; and so forth.

The statistics for 1913 furnish comparisons of these
compilations for a period of five years, and it is inter-
esting >to note how, even in this short period of time,
the tendency toward concentration of operations into
large units has progressed in the bituminous mines. In

the anthracite region of Pennsylvania such concentra-
tion had already been, practically accomplished to the
limit when the first attempt at this compilation was
made, but it is to be observed that even in this highly
centralised industry there has been an increase in the
number and percentage of the mines of the first class
and in the average yearly production by them. In
1909, 55-9 per cent, of the anthracite mines were of the
first class, and they produced 85-6 per cent, of the total
production, with an average production of 386,688 short
tons by each mine; in 1913 the first class mines
represented 62-6 per cent, of the total number, and con-
tributed 89-5 per cent, of the total output, with an
average per mine of 453,730 short tons. The number
and the total production of all the other classes in the
anthracite region were less in 1913 than in 1909. The
total number of producing mines in the anthracite
region has decreased from 304 in 1909 to 278 in 1913,
and yet the total production of the commercial mines
has increased from 76,813,562 short tons to 88,171,634
tons, and the average production of all mines in the
region was 317,164 short tons in 1913, against 252,676
tons in 1912. The average production per mine in the
anthracite region is nearly four times the average pro-
duction of 'the bituminous mines. The total number of
mines of the first class in the anthracite region in 1913
was 174, an increase of 4 over 1909, but the number
of all the other classes of mines has decreased from
134 to 104, indicating clearly that the concentration into
larger units in that region has been effected by the
closing down of about 25 per cent, of the smaller mines,
and operating the larger properties at greater capacity.
In the bituminous regions, with an increase of nearly
100,000,000 tons in the production from commercial
mines, there was one more mine in 1913 than in 1909,
the total number being 5,775 in the earlier years, and
5,776 in the latter. The most significant change was in
the number and production of the mines of the first
class. They were 539 on number in 1909, and 694 in
1913, the increase in the latter year being 155 mines, or
29 per cent. The total production from them showed
an increase of over 80,000,000 tons, from 160,929,762
tons in 1909 to 241,463,241 tons in 1913, and con-
stituted 80 per cent, of the total increase in the five
years. The average production per mine increased from
300,426 short tons to 347,930 tons, and the percentage
of the total production contributed by them increased
from 42-5 to 50-5. The number of mines of the second
class increased from 731 to 837, but there has been
relatively no change in the average production from
mines of this class, the average during the five years
ranging between 140,000 to 145,000 tons, and the
average in 1913 being a little less than in 1909.

There were seven States in 1913 in which more than
50 per cent, of the total production of bituminous coal
was from mines of the first class, but in one of these,
Georgia, only two mines were in operation, one of which
produced 235,892 tons, or more than 92 per cent, of
the total for the State. Of the States whose total pro-
duction exceeded 3,000,000 tons, Utah, a Rocky
Mountain State, led with 82 per cent, of its total pro-
duction from mines of the first class, and Montana,
another Rocky Mountain State, held the record in both
1912 and 1913 for high average production per mine,
three mines in that State having an average output of
555,720 tons in 1912, and 581,597 tons in 1913.
Virginia came next to Utah in its percentage of output
(71-8) from mines of the first class in 1913, and next
to Montana in its high average per mine—453,004 tons.
Pennsylvania had 66-7 per cent, of its bituminous pro-
duction in 1913 from mines of the first class, Illinois
had 66 per cent., New Mexico 62-6 per cent., and
Montana 54 per cent. Three of these States, it will
be noted, are in the Rocky Mountain region—public land
States; two are in the Appalachian region; and one in
the Central. West Virginia, the second State in the
Union in the production of coal, had only 37*6 per cent,
of its total output from mines of the first class. The
tendency toward operation in larger units is exemplified
in West Virginia, however, by the increase in the per-
centage of output from mines of the first class from
23-5 in 1909 to 37-6 in 1913. In 1909 there were 48
first-class mines in West Virginia, and in 1913 there
were 89. The total percentage of production of bitu-
minous coal from first-class mines increased from 49-2
in 1912 to 50-5 in 1913.

Shooting from the Solid.

The United States Geological Survey, in its report
on the production of coal, gives statistics of the quantity
of bituminous coal properly mined, either by hand or
by machine, and of the quantity and percentage shot
or blasted without having been previously undercut or
sheared. The method practised in the latter case is
characterised as “ shooting off the solid,” the only
preparation for which consists in drilling the holes
necessary for the explosive charge. The complaint is
made that in a few States this dangerous practice has
been indirectly encouraged by legislation, which compels
the payment for mining on the mine run, instead of the
screened-coal basis. The latest State to enact this kind
of law is Ohio, but, fortunately, in that State the danger
of increasing the quantity of coal shot off the solid is
somewhat lessened by the high percentage of coal mined
by machines, more than 90 per cent, of the total product
in 1913 being machine mined, and less than 4 per cent,
shot off the solid. It will be interesting to note if
operations under the new law, made effective in 1914,
show any appreciable changes in these proportions.
The heavy charges of powder necessary to blow down
the coal when it has not been previously undercut or
sheared result in the production of a much larger
proportion of fine coal, and render the lump coal so
friable that it disintegrates badly in handling and in
transportation. The principal offenders in the practice

of shooting off the solid are those States in which, for
more reasons than one, the contrary condition should
prevail, and that is in the States of the Middle West, Ln
what is designated as the interior province. In these
States the product is a dry, non-coking bituminous coal,
of which the slack or fine coal is not available in the
manufacture of coke; nor is the fine coal or slack as
satisfactory a steam fuel as the screened coal, and
like the small sizes of anthracite, it is sold at below the
cost of production. Of the total quantity of coal shot off
the solid (75,155,707 short tons), 38,253,166 tons, or
50-9 per cent., were produced in 1913 in the States of
Arkansas, Illinois, Indiana, Iowa, Missouri, and
Oklahoma. The entire production of Georgia in 1913,
96-5 per cent, of the production of Idaho, and all of
the production in Nevada, were reported as shot off
the solid, but in Georgia the fine coal is usable, and
is used in the manufacture of coke, and. in the other two
States the combined production is only a little over 2,000
tons. West Virginia stood at the head of the honour
roll in both years, with less than 1 per cent, out of a
total production of over 71,000,000 tons in 1913 shot off
the solid. Pennsylvania is a good second to West Virginia,
with 2’6 per cent, of its bituminous product shot off
the solid; Ohio came third, with 3-7 per cent.; and
Utah fourth, with 4'6 per cent. Three of these were the
three leading States in the Appalachian region, and two
of them—Pennsylvania and West Virginia—held the
first and second place in coal producing importance in
the United States. The quantity of machine-mined
coal increased from 210,538,822 tons, or 46-8 per cent,
of the total, in 1912, to 242,476,559 tons, or 50-7 per
cent., in 1913. The* hand-mined coal increased from
136,650,635 tons in 1912 to 141,555,532 tons in 1913,
but the percentage decreased from 30-4 to 29-6. The
powder-mined coal decreased from 76,241,575 tons to
75,155,707 tons, a decrease in percentage from 16-9 to
15-7.

THE GERMAN AND AUSTRIAN COAL
AND IRON TRADES.

We give below further extracts from German
periodicals that have reached us, showing the course of
the coal and iron trades in Germany and Austria :—

Coal Market in South Germany.

Transport difficulties, by water and rail, are the domi-
nating feature of the situation, the river traffic having
been greatly hampered of late by the low water and
prevalence of fog, in addition to the shortage of crane
men and other workers at the ports of shipment; whilst,
on the other hand, railway wragons have been very
scarce. In consequence, deliveries have fallen con-
siderably into arrear, and many industrial consumers
whose stocks are exhausted are in danger of having to
close down, or at least go on short time, for lack of fuel.
The demand is therefore pressing, more especially for
washed nuts, which are the grade most in arrear, and
are having to be replaced, as far as possible, by through
and through, screened slack, and briquettes. Owing to
the mild weather, the demand for house coal is not so
urgent, but even here the requirements of consumers
cannot be fully met in some grades, bituminous nuts in
particular. More anthracite nuts II., also, are being
asked for than can be supplied, but anthracite ovoid
briquettes are not in such demand for substitution as
heretofore. Moreover, the bulk of immediate needs has
been satisfied by means of Belgian coals. The stoppage
of exports to Switzerland has led to the accumulation
of small stocks at the transhipment ports; and the
reduced exportation of briquettes has lessened the output
of the works on the Upper Rhine, although they possess
ample stocks of small coal for the present. Broken coke
III. and gas coke continue scarce; and the gas com-
panies, whilst selling at low prices locally, ask rates even
higher than those of broken coke for the surplus. The
demand for brown coal briquettes is still active, stocks
being exhausted and new supplies delayed by the trans-
port difficulties. The Coal Syndicate is not making any
contracts for delivery beyond the end of the year, prices
being on the old basis, except for a small addition on
waterborne consignments on account of the rise in
freights.

German Steel Works Union Report for October.

The deliveries for October, calculated in weight of raw-
steel, amounted to 257,278 tons (246,840 tons in
September and 280,570 tons in October 1914), this total
being made up of semi-manufactured products, 68,344
tons (67,220 tons and 46,023 tons); railway super-
structural material, 130,981 tons (117,426 tons and
159,973 tons); and sections, 57,953 tons (62,194 tons and
74,570 tons).

German Pig Iron Output in October.

The Union of German Iron and Steel Manufacturers
reports an output of pig iron, during October, of
1,075,343 torus (1,034,124 tons in September), or 34,421
tons (34,471 toms) per working day. Of the above total.
185,305 tons (188,238 tons) were foundry pig: 1’4,627
tons (17,699 tons) Bessemer pig: 667,529 tons (639,362
toms) basic pig; 188,516 tons (170,602 tons) steel-iron and
spiegeleisen: and 20,366 tons (18,225 tons) puddling pig.
The production in the various districts was as follows :
Rhenish Westphalia, 472,275 tons (462,393 tons);
Siegerland. Wetzlar, and Hesse-Nassau, 71,579 tom
(66,115 tons); Silesia, 66,952 tons (64,559 tons); North
Germany, 20,259 tons (20,262 tons); Mid Germany,
33,307 tons (32,261 tons); South Germany and
Thuringia, 21,071 tons (18,658 tons); the Saar district,
72,316 tons (69,418 tons); Lothringen, 174,070 tons
(160,259 tons); and Luxemburg, 144,514 tons (140,199
tons).

Company Reports.

TVcrschen-Weissenfelser Braunkohlen A.G., Halle.—
To the trading profit of 3,153,406 mk. (2,844,535 mk.)
must be added 218,338 m. (331,091 mk.) brought forward