68

THE COLLIERY GUARDIAN

July 14, 1916.

CURRENT SCIENCE AND TECHNOLOGY.

Naphthalene as Motor Fuel.

A recent issue of the American Gaslight Journal stales
that naphthalene, as a motor fuel, is cheap, and has
particular technical advantages. It contains less
hydrogen than benzene, and being a product of high
temperatures, is stable, and has a high temperature of
ignition, which is an advantage for motor purposes,
since it admits of higher compression being used. Pure
naphthalene is white, melts at 175 degs. Fahr., and boils
under 760 mm. pressure, at 424 degs. Fahr. The interval
between melting and boiling points favours the use of
naphthalene in the liquid state. The specific gravity of
the liquid at 80 degs. Cent, is 0-977; that of the solid at
15 degs. Cent, is 1*15. Its fusion is easy, as the latent
heat of fusion is only 36 calories. The high vapour
pressure is noteworthy, and is responsible for the diffi-
culty of removing it from coal gas; but in a motor it
facilitates the formation of practicable mixtures of the
fuel and air.

Theoretically, 1 lb. of naphthalene needs 162 cu. ft.
of dry air for complete combustion. The complete com-
bustion of the vapour is attended by an increase in
volume, 13 volumes of a mixture of naphthalene and
oxygen yielding 14 volumes of carbonic acid and water
vapour. The gross calorific power of naphthalene is
9,600 calories per kilog. (17,280 British thermal units
per pound); but the net calorific power is only 9,300
calories (16,740 British thermal units per pound).
Naphthalene is insoluble in water, but is dissolved by
the following solvents in these percentages by weight;
alcohol, at lOdegs. Cent., 5’00 per cent.; petroleum
ether, 11*05 per cent.; benzene, 40-70 per cent.; toluene,
35*30 per cent.; xylene, 29*00 per cent. The addition
of naphthalene to benzene lowers the freezing point of
the latter—an important point in motor benzol for use
in cold weather. Benzol, which crystallises at 41 degs.
Fahr., on the addition of 30 per cent, of naphthalene,
deposits no solid matter at 26 degs. Fahr.

Naphthalene has the advantage of yielding a vapour
of uniform composition, but it has to pass from the solid
through the liquid state before vaporisation. Hence
a naphthalene engine must have a vessel for melting the
naphthalene, kept hot enough to prevent solidification.
The first practicable engine was produced by the Deutz
Gas Engine Works in 1907, and in 1914 there were about
1,000 such engines at work. The engine is generally a
single or two cylinder four-cycle horizontal engine,
similar to the Otto. On the cylinder, with the cooling
jacket, is a double-walled naphthalene fusing tank, from
which a heated tube leads to the carburetter through a
float-valve. In the later Deutz engines there is a small
water-tube boiler (heated by the exhaust gases), which
raises the temperature of the cooling water to boiling
point quickly after the engine is started, and the
naphthalene is melted more quickly than in the old type.

These engines start cold with gas or liquid fuel. After
running awhile and becoming warm, the change-over is
made to naphthalene; or an independent source of heat
may be used to enable the engine to start direct on
naphthalene. The engines have only been made in sizes
of 4 to 20 horse-power per hour ; but in consequence of
the increase in the price of liquid fuels caused by the
war, larger units are now being constructed.

Efficiency tests made on a Deutz six horse-power
naphthalene engine showing the consumption of fuel
per horse-power hour at half load and full load, gave the
following result :—

Fuel consumed
per h.p.-hour.

Gasoline .......

Benzol .........

Naphthalene ....

Half-load.

Oz. Cost (c.).

16*6 ... 4*30 ...

14*1 ... 2*90 ...

13*4 ... 1*10 ...

Full load.

_______A_________

Oz. Cost (c.).

11-3 ... 2*94

9*5 ... 1*95

10'2 ... 0'85

In this table the cost of motor spirit is taken at
95dels. (£19 15s. lOd.) per ton, benzol at 74-50
(£15 10s. 5d.), and naphthalene at 30 dels. (£6 5s. 5d.).
The figures are extremely favourable for naphthalene.
The cost of operating, including interest, depreciation,
attendance, lubrication, and fuel, works out at 2-50 to
4*25 c. for the benzol engine, and 1*70 to 2-80 c. for the
naphthalene engine, per horse-power hour. The naph-
thalene engine shows to the best advantage on long runs.
For some purposes it is best to liquefy the naphthalene
by means of a solvent, and most of the attempts to use
naphthalene have been made with its solution in benzol.
A saturated solution, when cooled, deposits solid
naphthalene, and the same thing occurs on evaporation
of the solvent. Hence the mixture must be well below
the saturation point, and additions of comparatively
small proportions of naphthalene <to benzol have been
used with complete success in automobile engines. The
use of naphthalene as a fuel for small engines can be
extended with advantage, particularly for commercial
motor vehicles.

Spontaneous Ignition of Coal.

In an article in Het Gas upon the spontaneous
heating of coal, A. P. Bruigum rejects the ordinary expla-
nation that it is due to the presence of iron pyrites,
because if iron pyrites, in small grains and moistened
with water, be exposed to a stream of oxygen, there is
hardly any appreciable rise of temperature, even when
the oxygen is charged with ozone. Indirectly, the
presence of iron pyrites may assist a reaction primarily
due to other causes, through the production of a layer of
ferrous oxy-sulphate; but the main cause must be sought
for elsewhere. Coal contains three main components :
of these bitumen (i.e.,the components soluble in benzol,
benzene and the like) is a dark mass which fuses at from
80degs. to 90degs. Cent., has a specific gravity of about
1, 0-13 to 1-66 per cent, of sulphur and not over 4 per
cent, of ash. After dissolving out the bitumen, treating
the sample with a solution of caustic soda, extracts
humic acid, which can be precipitated by a mineral acid,

and has the property, in presence of alkali and air, of
taking up nitrogen. The residue consists of humin (made
up more or less of cellulose), to which is due the weather-
ing and deterioration of coal, with loss of carbon and
hydrogen and increase in the percentage of oxygen and
of ash, and a fall-off in the heating value. This weather-
ing is most pronounced in the layers most exposed 'to the
air; if the coal be dry the weathering is very slow, but if
damp is greatly accelerated. The yield of tar from
weathered coal is much less than from fresh coal, but
is richer in paraffins. During weathering this third com-
ponent, the humin, undergoes gradual combustion, and
the humic'acid undergoes changes in presence of oxygen,
under the action of microbes, with formation of CO2.
This acid will take up much free bromine and ozone.
With the ozone it forms ozonides, which are decomposed
in presence of moisture, liberating heat and carbon
dioxide. In the absence of ozone coal absorbs a good
deal of oxygen, but holds it simply as an absorbed gas;
the process of chemical combination is very slow at
ordinary temperatures, but becomes rapid when the
temperature is raised, and as the temperature is raised
the absorption of oxygen becomes greater. The reaction
therefore tends to produce progressively rising tempera-
tures, culminating in some cases in spontaneous com-
bustion. For an effective start, however, ozone is essen-
tial, and this is formed wherever evaporation of water
takes place. A damp heap of coal is, therefore, bound to
start weathering; and if the circumstances are favour-
able to this the temperatures will begin to rise, and the
inactive oxygen begin to help in the process of destruc-
tion. This explains why warm weather after rain is
dangerous to coal in heap, and why the damp sea air,
laden with ozone, is dangerous .to the coal in shipts’
bunkers; and it would appear that ventilation of the coal
may import its own special risks. There is never any
risk of spontaneous combustion of coke or of anthracite;
it is the humic acid and humin of coal that cause the
phenomena of weathering, heating up and spontaneous
ignition.—Gas World.

The Coolest Roof Material.

Dealing with the work at the National Physical
Laboratory, Engineering gives some details of the
transmission of the sun’s heat through roofing materials.
Corrugated iron has its great conveniences, but any-
body who has had to stew in such a shed during day-
time and to shiver during the night would welcome the
replacement of the galvanised iron roof by something
less pervious to heat. Unfortunately, the tests of some
new cheap roofing materials, consisting of cement and
fibrous material, compressed to sheets £in. and more
in thickness, are not at all promising in this respect,
though the thermal conductivity of cement-like materials
is about one-seventieth that of iron. In the experi-
ments at the laboratory, a model hut was built up of
walls of cork slabs, 2 in. thick, and a roof of the new
material or of galvanised sheet iron; the air inside was
heated by resistances which were not allowed to get
sufficiently hot to set up appreciable radiation, and the
air was agitated by a fan; the air temperature inside
and outside differed by 30 degs. Fahr. Contrary to
expectation, the heat loss through the cement, measured
per square foot, was 20 per cent, greater than through
iron, the reason being that the emissivity loss from the
surface, and not the thermal conductivity of the
material, is the decisive factor. When the iron was
painted black, the heat transmission increased, becoming
equal to that of the cement; when the cement slabs
wrere painted with aluminium they behaved like the
iron; the gradient in the material was only 2*5 degs.
Fahr. Possibly the material might answer better when
made in cellular form, with air spaces, if then suffi-
ciently strong.

Internal Friction of Metals and Temperature.

While the internal friction of liquids has been much
investigated, the internal friction of solid bodies has
not received sufficient attention, and there is indeed no
general agreement as to the meaning of the term. In
describing his recent investigation of the change of the
internal friction of metals with temperature (Zeitschrift
physikalische Chemie, vol. xcl., pp. 232-47, 1916), Prof.
P. Ludwik, of Vienna, defines the internal friction R
as that specific tangential stress which is required to
cause a permanent relative displacement of the par-
ticles. In liquids the R would, in the first instance,
depend upon the specific rate of displacement v and the
temperature t; for v = 0, R would be 0 for liquids; but
for solids R might be greater than 0, because any pre-
vious strain y would have to be considered, and the
R would generally increase with increasing y, though
it might decrease. In order to eliminate the influence
of y > the metal was submitted to a thermal treatment.
The R, Ludwik has pointed out in his various memoirs
on the testing of materials, can be deduced from the
test diagrams. In the present research he simply deter-
mines the hardness by the cone-pressure method, and
he plots the hardness numbers found—the pressure in
kilogrammes divided by the area of the resulting
impression circle in square millimetres — as ordinates
against the temperatures as abscissae. The pressure,
ranging from 5 up to 1,000 kilogs., was applied by means
of an Amsler machine, either rapidly within 30 seconds,
or slowly within 300 seconds. The cone-angle was
90 degs. The metals experimented upon were of the
highest commercial purity; there was some doubt as to
the purity of the bismuth and antimony, however; the
copper was electrolytic. The specimens were fused
under layers of salts, cast and annealed; the specimen
plate was laid on a plate of steel within the electrically-
heated bath, which consisted of a cylinder oil for
temperatures up to 300 degs. Cent., and of nitrates for
temperatures up to 600 degs. Cent.; the range investi-

gated was 20 to 600 degs. Cent. A fairly steady decrease
of the hardness with rising temperature was observed
in all the cases. The curves were nearly straight, or
only slightly hollow (when the hardness diminished,
first rapidly, and then slowly) in the case of tin and
bismuth; cadmium, lead, zinc, antimony yielded more
hollow curves; aluminium and copper yielded graphs
curved in the opposite sense and somewhat S-shaped,
i.e., the decrease in hardness with rising temperature
was first slow, and became more rapid afterwards, to
diminish again. There was some questionable indica-
tion of the influence of the different modifications of a
metal in the case of tin, e.g., but those influences
appeared weak, whilst tensile tests of iron and nickel
show a decided influence of the allotropic modifications.
All the metals heated up to their melting points pos-
sessed still considerable hardness immediately before
melting, when the internal friction of the solid would
thus appear suddenly to pass into the viscosity of the
molten metal. Thus, near its melting point, tin (and
also bismuth) still marked 10 per cent, of its internal
friction at 20 degs. Cent.; lead went down to 7 per cent.,
cadmium to 2 per cent., zinc to per cent, of the
original R. When the curves for the different metals
are plotted in one diagram, some of the hardness curves
are seen to cross; this holds for equal temperatures, as
well as for homologous temperatures; in the latter case
the melting point temperature is taken as unit. This
shows that the change of hardness with temperature is
not uniform for different metals. The rate of applying
the pressure has also to be considered; the above-given
figures for the reduction of the hardness refer to slow
loading.—Engineering.

LETTERS TO THE EDITORS.

The Editors are not responsible either for the statements
made, or the opinions expressed by correspondents.

All communications must be authenticated by the name and
address of the sender, whether for publication or not.
No notice can be taken of anonymous communications.

As replies to questions are only given by way of published
answers to correspondents, and not by letter, stamped
addressed envelopes are not required to be sent.

MINING SURVEYORS’ EXAMINATIONS, Ac.

Sirs,—The correspondence in your columns re mine
surveyors is now touching on a point which has been
neglected far too long.

The present day colliery surveyor has to be an expert
at his work, or he may cause his employers to lose con-
siderable time and money, should he fail in any of the
important thurls, which are so often met with in modern
mining.

What has he to encourage him to make himself a
really good man? He certainly has not the salary.

If he should give all his time to his work, he will find
at 25 years of age he is not qualified to sit for his
manager’s certificate, however much experience he may
have had. How can he therefore specialise on surveys
which bar him from the only other class of work,
namely, managing?

If something could be done to make the position
worth while, it would, I think, result in the work being
under the control of fully qualified men of staid years,
and not of youths, who are simply in the position for
the time being.

I think the formation of a surveyors’ institute, as
suggested a year or two ago, could do much to rectify
the matter.	Surveyor.

July 8, 1916.

Sirs,—With reference to “ Old Surveyor’s ” letter in
last week’s issue, I think the time is now ripe for mining
surveyors to do something to better their status. The
average salary paid to the experienced surveyor is
simply scandalous when compared with what other
branches of the mining industry are paid. A regular
working collier can laugh at a surveyor’s wage, and his
son need never trouble about “ how to become a sur-
veyor ” if he only knew the truth.

It will be interesting to see what becomes of the large
number of surveyors who have taken up commissions in
the tunnelling companies. As officers they have some
status and good pay, and have been doing good work for
their country, but not any better than they were doing
for their employers before the war, and for which they
had very little recognition. I think, in fairness to them,
we should form an institution which will look after their
interests as well as our own. There is no use sitting
still and waiting for our employers to look kindly upon
u>s: any improvement will only come from a collective
effort. I think as a profession we can be forgiven if we
have some sympathy with the miners in their struggle
for higher wages, which have only been obtained by
virtue of their strong organisation.

There is much to be said for a surveyors’ institute, and
the masters stand to gain equally as well if they only
knew it. How*ever, it is unfortunate that surveying
doesn’t figure as a separate item on the cost sheet,
although it does indirectly in some companies when the
endeavour has been to have the surveying done on the
cheap.	Tunneller.

Hull Coal Exports.—The official return of the exports of
coal from Hull to foreign countries for the week ended July 4
is as follows :—Alderney, 134 tons; Alexandria, 576; Amster-
dam, 713; Calais, 892; Dunkirk, 697; Gothenburg, 2,113;
Harlingen, 635; Rotterdam, 738; Stockholm, 1,308; Treport,
5,774; Honfleur, 909; Norrkjoping, 1,885; Rouen, 1,649—
total, 18,023 tons. Corresponding period July 1915—total,
38,857 tons. These figures do not include bunker coal, ship-
ments for the British Admiralty, nor the Allies Governments.