906

THE COLLIERY GUARDIAN.

November 10, 1916.

experiments have proved that persons engaged in dis-
tributing the dust, and who are therefore most expoatm
to it, have not contracted silicosis to the slightest exueni.
Stone dusting is practised at five mines, and below is
shown the state of the mine, the quantity of stone dust
sent down monthly, and the number of persons engaged
in distributing it:—

Coiliery.	Condition. Tons. Boys.”

Durban Navigation	Fiery and dusty...	35	...	10

Cambrian ........ Do. do. ..... 50 ... 10

Glencoe ......... Do. do.&gobfires 80 ... 16

St. George's .... Slightly dusty ....... 8	...	1

Burn ide......... One dusty road......	3	...	—

Nothing has been done in the way of rescue stations
or training men to use rescue apparatus. It is univer-
sally admitted that a rescue apparatus is a death trap
unless a man has been thoroughly trained to its use by
a competent instructor. It is doubtful whether there
is a competent instructor in South Africa. For this
reason the apparatus is never used in Natal. On the
Rand, if a man is gassed, it is usually in a winze, and
given that the air pipe is down, the rescue can usually
be effected by turning on the air. But in dealing with
fires or explosions at a colliery, a long distance in
poisonous gas has to be travelled, and if a man goes in
with a defective apparatus, he probably would not come
out alive. Under the circumstances, and until a pro-
perly equipped station and competent instructor can be
obtained, it has seemed better to ignore rescue apparatus
and to go on the old methods of keeping a supply of
good air to the men engaged in building stoppings;
when this cannot be done, the men have to work as
long as they can, and be replaced by others as soon ais
they get affected by carbon monoxide. There is no
doubt that on two occasions in the past year a trained
team would have been of great value in building stop-
pings and isolating fires quicker than was done. It is
to be hoped that no time will be lost in establishing a
rescue station, once the war is over.

THE GERMAN COAL AND IRON
TRADES.

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

Goal Syndicate Report for September.

Total coal raised, 7,854,955 tons (8,232,179 tons in
August), or 302,114 tons (304,896 tons) per working
day; calculated distribution, 5,972,012 tons (6,531,801
tons), being 229,693 tons (241,919 tons) per working
day, or 63-56 per cent. (66*93 per cent.) of the partici-
pation; total coal distributed, 7,780,322 tons (8,369,512
tons), or 299,244 tons (309,945 tons) per working day;
deliveries, including local sales, miners’ house coal, and
supplies to pits’ own iron works : coal, 4,128,533 tons
(4,435,299 tons), or 158,790 tons (164,270 tons) per work-
ing day; coke, 2,175,471 tons (2,363,449 tons), or 72,156
tons (76,240 tons) per working day; briquettes, 314,391
tons (347,110 tons), or 12,092 tons (12,856 tons) per
working day. As already reported, the meeting of the
members agreed to the renewal of the Syndicate until
March 31, 1922.

Increased Retail Prices for Iron.

The Elberfeld-Barmen Iron Merchants’ Association
has raised the price of stock bars, hoop iron, and weld-
ing iron by 30 mk. per ton, and that of plate by 30 to
50 mk., very thin plates also bearing a small additional
charge.

German Output of Medium Steel in September.

According to the report of the German Iron and Steel
Manufacturers’ Association, the output of medium
steel in September amounted to 1,393,434 tons (1,414,097
tons in August), or 53,594 tons (52,374 tons) per work-
ing day. Of this quantity, 653,894 tons (658,588 tons)
were basic Bessemer steel, 16,752 tons (14,247 tons)
acid Bessemer, 570,842 tons (580,028 tons) basic open
hearth, 14,871 tons (21,145 tons) acid open hearth,
71,337 tons (74,483 tons) basic cast steel, 38,302 tons
(38,315 tons) acid cast steel, 9,961 tons (10,228 tons)
crucible steel, and 17,475 tons (17,093 tons) electro
steel. Rhenish Westphalia produced 789,759 tons
(799,346 tons); Silesia, 115,760 tons (123,529 tons);
Siegerland and Hesse-Nassau, 28,423 tons (28,413 tons);
North, East, and Mid Germany, 60,712 tons (61,319
tons); Saxony, 29,814 tons (30,508 tons); South Ger-
many, 13,235 tons (13,188 tons); the Saar district and
Bavarian Rhinepfalz, 118,859 tons (117,587 tons);
Elsass-Lothringen, 129,910 tons (127,815 tons); and
Luxemburg, 107,142 tons (112,392 tons). For the first
nine months of the current year the output was
11,930,000 tons, as compared with 9,673,000 tons in the
corresponding period of 1915, and 12,250,000 tons in
1914.

Steel Union Report for October.

In semi-manufactured products, the home demand
continued active, and difficult to satisfy completely; but
trade with neutrals was entirely suspended. The Prus-
sian State Railways placed orders for their immediate
requirements in heavy super-structural material. Tram
rails were in fair request, and orders were plentiful for
pit and light railway rails, both from collieries and the
army authorities. Export trade quiet. The home
market for sections showed an increased demand for
military purposes, so that little was available for other
users. Enquiries from neutrals were numerous, but,
with few exceptions, could not be complied with, owing
to the great increase in the home consumption.

Dr. J. Wilson has been appointed certifying surgeon, under
the Factory and Workshops Act, for the Irvine district.
Similar positions are vacant at Crossgar (Down) and
Lancaster.

CURRENT SCIENCE

Sensitiveness of T.N.T. and Tetryl to Detonation.

In Technical Paper 145 (United States Bureau of
Mines) Messrs. G. B. Taylor and W. C. Cope describe
tests made on the sensitiveness to detonation of tetryl
and T.N.T., and mixtures of same prepared by fusing
together the two substances, and obtaining careful cool-
ing curves. The cooling curves were obtained from
different masses of melt, and under widely different rates
of cooling, but the authors were unable to confirm Gina’s
conclusion that an unstable compound of three mole-
cules of T.N.T. to two of tetryl is formed. The ten-
dency of the melts to supercool was great, and the heat
effects of the crystallation were so small as to render
methods of thermal analysis untrustworthy. The tests
were carried out as follow :—Exactly 0-4 grm. of the
explosive was weighed into a copper shell, 5 mm. in
diameter, and slightly pressed with a neatly fitting glass
rod, having a fiat end. The primer (90 per cent, mer-
cury fulminate and 10 per cent, potassium chlorate) was
placed on top, and the thin copper reinforcing cap
(9 mm. long, with 2*3 mm. perforation) was inserted,
and pressed down into the shell for one minute under a
loading pressure of 200 atmospheres per sq. in. (206
kilogs. per sq. cm.). A short piece of fuse was crimped
into the shell, and the detonator fired in the sand bomb.
The results show that, whereas T.N.T. required
0*25 grm. of primer for complete detonation, tetryl
could be completely detonated with 0*19 grm., and that
the sensitiveness of the mixtures of the mixtures
increased in direct ratio to the proportion of tetryl.

The sensitiveness of T.N.T.-tetryl mixtures to moist
fulminate mixture was also determined. A number of
detonators were made up as above described, contain-
ing charges of 0-4 grm. base charge and 0-32 grm. of
90 : 10 priming charge. These were stored over water,
and tested from time to time. The pure T.N.T. failed
when the detonator had taken up 0-0030 grm. of mois-
ture ; 10 per cent, tetryl detonated when the moisture
content was 0-0037 grm., and failed when the moisture
content was 0*0048 grm.; 50 per cent, tetryl detonated
when the moisture content was 0*0048 grm., and failed
when the moisture content was 0*0055 grm.; and the
pure tetryl cap still detonated with a moisture absorp-
tion of 0*0062 grm. Lead hydronitride, or lead azide
(PbHr) seems to have a distinct preference for deto-
nating tetryl. The authors have found that as little as
1 milligrm. -will often detonate tetryl, and that 0*01 grm.
will always do so. The minimum charge for T.N.T. under
a loading pressure of 200 atmospheres is 0*23 grm.; with
a pressure of 400 atmospheres it is about 0*15 grm.
Martin found the minimum charge to be 0*09 grm.
under a loading pressure of about 1,000 atmospheres.

Blasting with Liquid Oxygen.

Since 1915 experiments with liquid oxygen cartridges
have been earned out at the Winiterhall salt mines with
considerable success. According to Heberle (Kali), the
cartridges used are made of fabric, paper, or cardboard,
and are charged with lampblack, or with kieselguhr and
petroleum. A cap of mercury fulminate is generally
added for ignition, but should only be loosely connected
with the cartridge, to facilitate impregnation of the
carbon. The Marsit cartridge does not need any cap.
Ignition is by fuses or by electric wines; and Hecker is
said to have introduced ignition devices which do not
necessarily ignite all the cartridges in a circuit simul-
taneously. The pre-cooled material may be impreg-
nated either by pouring the oxygen into the cartigdge
through a tube of filter paper, or by immersing the cart-
ridge in the liquid, the latter being preferable. The
oxygen should be 99 to 97 per cent. pune. The immer-
sion of a cartridge takes from five to 25 minutes. The
experiments established that a cartridge can be so
impregnated that it will still explode 10 or 15 minutes
after being tamped in the hole; and means have even
been devised whereby cartridges can be impregnated at
the surface, and be taken down and used two or three
hours later.

Spark Ignition.

Two opposed schools of belief find adherents
among engineers (says Engineering) regarding the
effects of spark intensity on ignition in internal com-
bustion engines. According to the one, provided a
spark is sufficiently strong to produce ignition, an
increase of strength has no effect on either the rate of
combustion or the maximum pressure attained; conse-
quently, such increase has no effect upon the power
developed by the engine. According to the other, the
strength of the spark does have an effect upon the
power, and it is therefore assumed that the spark
strength influences both the rate of combustion and the
maximum pressure attained. Obviously, both asser-
tions cannot be true, yet it is possible that the one which
is untrue has some foundation in fact, and has arisen
out of a misinterpretation of experimental results.
Regarding the terms “ strength ” or “ intensity,” as
applied to sparks for ignition purposes, no clear mean-
ing is or can be attached to them. The terms are
unsuitable, because, as ordinarily used, they refer to
the total heat energy of a spark, and this alone does
not determine the ability of a spark to ignite a given
gas mixture. To meet the difficulty, the term “ incen-
divity ” has been proposed to denote the property
whereby a spark produces ignition of a combustible gas".
The question arises : What ground is there for the belief
that engine power is affected by the incendivity or
so-called strength of the igniting spark? The answer
is to be found in the fact that an explosive gas mixture
requires for its ignition a spark having not less than a
certain incendivity, and the latter varies with the nature
and proportions of the mixture. When the proportions
of the mixture are at or near the upper or lower limits

AND TECHNOLOGY.

beyond which ignition is impossible, the required incen-
divity is high. But as the proportions approach that of
maximum explosibility the required incendivity rapidly
diminishes, Hence, for a given gas mixture, a certain
minimum incendivity is necessary in the spark. If the
incendivity is near the limit, a diminution in the explo-
sibility of the mixture may result in no ignition, or only
intermittent ignition. This can be rectified by employ-
ing a spark of higher incendivity, providing a greater
margin for gas variations. In a petrol engine, particu-
larly when running at slow speed, weak mixtures
requiring strong sparks for their ignition are often
obtained, and when the ignition system is insufficient
to provide suitable sparks, defective operation of the
engine ensues. On replacing the ignition system by
another producing stronger sparks, the engine works
satisfactorily. Arguing from this, the user concludes
that the better spark has increased the power of his
engine by’increasing the rate of ignition or the maximum
pressure, whereas actually it has only eliminated miss-
fires.

REFRACTORY MATERIALS.

On Wednesday, 8th inst., a general discussion on the
subject of “ Refractory Materials ” was held by the
Faraday Society, at the Institution of Electrical
Engineers. Sir Robert Hadfield, who presided, de-
livered an introductory address, in the course of which
he expressed the hope that the meeting would draw
general attention in this country to the subject, specially
as in ferrous metallurgy any improvements in practice
which add to the increased life and efficiency of steel-
melting furnaces mean more output in a given time, a
point of such vital importance in this war-time. These
direct metallurgical operations cannot claim to put the
burden of working out improved practice upon the
workman ; it is the “ master ” himself who must study
out new developments

Amongst others in this country who have taken
special interest in the subject of refractories are the
following : Dr. J. W. Mellor, of the Staffordshire County
Pottery Laboratory, who has paid so much attention to
this question and who is no-v conducting a research for
the Advisory Council of Scientific and Industrial
Research; Dr. H. G. Colman, chairman of the Joint
Refractory Materials Committee of the Institution of
Gas Engineeis and the Society of British Gas In-
dustries; Major F J. By water, now on active service,
who was formerly chairman of the above-mentioned
Committee, is the author of an excellent paper on
“ Refractory Material ” read before the Institution of
Gas Engineers; Mr. F. W. Harbord, who is also
engaged in conducting enquiries and researches with
regard to refractories in connection with another special
committee; Prof. W. A. Bone, the chairman of the
Fuel and Refractories Committee of the British
Association; Prof. W. G. Fearnsides, of Sheffield
University; Dr. B. G. H. Boswell, Dr. A. Strahan, and
Mr. J. Allen Howe, of the Geological Survey Museum,
Mr. Ezer Griffiths, M.Sc., National Physical Laboratory,
and Messrs. Cliff, Page, and several others who took up
the matter from the point of view of the manufacturers.

The Institution of Gas Engineers issued in 1912
an interesting specification for refractory materials
(“Standard Specifications for Refractoiy Materials”),
covering (a) firebricks, blocks, tiles, etc.; (b) silica
bricks, blocks, tiles, etc. It seems a pity that the
subject has also not been brought more prominently
before our leading societies devoted to metallurgy, as
undoubtedly there is a general scarcity of technical
literature on the subject.

The Chief Refractories. — The following probably
represents the chief refractories .*—(a) silica; (5) china
clay; (c) magnesite; (d)- dolomite; (e) chromite;
(/) bauxite; (g) graphile; (h) zirconite. There have
been considerable importations into our country from
abroad of refractories, when without* doubt in most
cases equally as good, if not better, material has been
in our own country at our very door. Moreover, this
subject not only interests the ferrous and non-ferrous
metallurgist, but also the makers of the various pottery,
porcelain, and other similar wares. Special thanks are,
therefore, due to Dr. Strahan, Mr J. Allen Howe, and
Dr. Lam plough, of the Geological Survey and Museum,
Jermyn-street, who have quite recently taken up the
subject most vigorously and shown that at home in our
own kingdom we possess more valuable stocks of raw
products to be used for the purpose of refractories
than has been ordinarily imagined. Prof. W. R.
Dunstan, F.R.S., of the Imperial Institute, has also
given attention to this subject.

Ganister.— The great importance of obtaining a good
refractory is shown by the fact that the first develop-
ment on a large scale of the Bessemer process in
Sheffield was chiefly because there happened to be in
that city a particularly fine quality of material known
as “ ganister.” Sir Henry Bessemer could not find
material suitable for lining his converters, in which
there is a combination of not only high temperature but
slagging and erosive action. Sheffield ganister was
found to meet this condition better than any other
material, thus enabling Bessemer to carry his process
into practical working success.

The following is a typical analysis of ganister:—
Silica, 95 per cent.; alumina, 2 per cent.; iron oxide,
0*5 per cent.; lime, 1’00 per cent.; magnesia. 0*6 per
cent.; water, 1 75 per cent. This material has been used
for several generations to line the furnaces (“potholes”)
in which Sheffield crucible steel is made, and it is still
unsurpassed for this purpose.

In his paper, already referred to, Major Bywater has
given an interesting resume with reference to the origin