1080

THE COLLIERY GUARDIAN.

June 8, 1917.

CURRENT SCIENCE AND TECHNOLOGY.

Estimation of Benzene and Toluene in Coal Gas.

Mr. B. P. Rothkopf (Gas World) has been carrying
out a series of tests with various oils to determine
their relative capacity for benzol extraction, employing
the apparatus illustrated, which can be constructed
in the works, only requires glass apparatus of a kind
that is generally available, and enables 100 cu. ft. of
gas to be completely washed in less than 24 hours
without necessitating attention after the test has once
been started.

3Y

In order to obtain a regular flow of oil, a three-litre
aspirator A is employed, fitted with a '1 in. delivery pipe
and stop cock, the oil
dripping from the end
of this pipe into the
open top of the oil-
inlet syphon to the
scrubber. The top of
the aspirator is closed
with a perfectly
fitting rubber

stopper through which passes a
narrow glass tube B open at both
ends and reaching to within J in. of
the bottom of the aspirator, so that
the oil pressure on the delivery pipe
remains constant as the level of the
oil in the aspirator becomes lower.

To regulate the rate of flow of the
oil, a cork, fitted with a length of
capillary glass tube of about 1 mm.
diameter, is placed in the inner end
of the s in. delivery tube G. The
length of capillary tube required to
give a delivery of about 100 c.c. per
hour must be found experimentally
for the oil used, as this varies
according to the viscosity of the oil.
This is done by fitting a piece of
capillary tube of, say, 4 in. in length
in the outlet tube and ascertaining
the amount of oil delivered by this,
the oil reservoir being as full as
possible and the rate of delivery
being measured as soon as air enters
the bottle from the bottom of the
tube B. The length of the capillary

tube is then shortened or increased accoi ding as the
rate is too slow or too fast, until a length is found with
which the rate is not less than 100 c.c. per hour, or 10 c.c.
in six minutes. To prevent the capillary tube becoming
blocked, the oil used should always be strained before
use to remove any solid particles. If this is done, t he
flow of oil keeps constant without supervision.

The most suitable form of scrubber for the purpose
consists of a piece of 2 in. pipe 24 in. long, filled with
J in. Raschig rings. (These may be made by culling
off pieces of | in. metal pipe § in. long; or by cutting
off J iii. lengths from a tube of metal obtained by
bending thin sheet metal round a t in. pipe.) A
scrubber of these dimensions and filled with these rings
is capable of effecting the complete removal of the con-
densable vapours from coal gas passing at the rate of
5 cu. ft. per hour, by the use of an oil flow of about
100 c.c. per hour, if creosote or green oil is employed as
the absorbing oil. This figure applies to a gas contain-
ing not more than 2 g Js. of crude benzol per ton of
coal carbonised. With a richer gas the oil supply must
be slightly increased or- the rate of flow of the gas
decreased.

To the bottom of the scrubber is fitted a 2 in. to J in.
diminishing socket, in which a perforated plate D is
placed prior to fixing. The plate should be about 1A in.
diameter, and its function is to support the rings used
as scrubber filling. A piece of tube is screwed into the
side of the D socket, and bent upwards as shown,
serving as the gas inlet (after the meter), and a syphon
of “ m compo ” pipe is fixed into the end of the D socket
to form the oil outlet. Before using the apparatus it
is preferable to solder all joints at the bottom to render
them oil-tight. The top of the 2 in. pipe is closed by a
good cork, through which pass the inlet oil syphon G
and the gas outlet pipe H, from which the scrubbed gas
may be led direct to a burner, the appearance of the
flame giving an approximate guide to the completeness
with which the extraction is proceeding. The whole of
the 2 in. pipe is filled with Rasehig rings, which are
ponied in indiscriminately, so that they occupy irregular
positions throughout the scrubbing space.

The oil used may be creosote, green oil or gas oil.
The oil should be previously distilled until a thermometer
in the vapour registers 230 degs. 0., the residue being
employed after good cooling and filtering off from
naphthalene or other separated solid matter. Gas oil,
if used, must be passed into the scrubber at the rate of
about 140 c.c. per hour.

In commencing a test the oil is first turned on, and
when this drips from the end of the oil outlet syphon
the gas is turned on. The gas is regulated to a rate of
5 cu. ft. per hour and passes through a governor and
meter before entering the scrubber. At the conclusion
of the test the gas is shut off and the oil allowed to flow
for another hour. The gas passed is determined from
the meter readings at the commencement and end of
the test, the usual temperature and barometer observa-
tions being made. If the test has to be carried out
at a place where the temperature is high, the scrubber
should be provided with a water jacket for cooling
purposes. The resulting benzolised oil is distilled and
the amounts of benzene, toluene, etc., ascertained in the
usual manner.

Effect of Burning Coal on Overlying Strata.

According to the U.S. Geological Survey Press
Bulletin No. 314, many coal beds in the great coal fields
of the Western States have at some time taken fire and
burned along their outcrops, baking and reddening the
overlying strata so that they have become a kind of
natural brick or terra-cotta. The fires were in places

hot enough to fuse and recrystallise the overlying shale
and sandstone so as to form natural slag. At some
places this slag resembles true igneous rock ; at others
it consists largely of rare minerals. Thoroughly fused
slag seems to occur chiefly in crevices or chimneys
through which the hot gases generated in the burning
escaped through the overlying strata to the surface.
The chimney-shaped masses of slag are harder than the
surrounding baked rock and, after that has weathered
away, form the curious pinnacles that surmount many
clinker bluffs or buttes in the west.

Some of the coal beds, especially those exposed on
the higher hills, were perhaps ignited by lightning;
others, according to well-authenticated reports, were
ignited by prairie fires or camp fires; but as burning on
the outcrop has been so common as to affect most of
the coal beds in an area of more than 200,000 square
miles, much of it has probably been due to spontaneous
combustion.

Coal beds are now burning at or near the surface at
many places in the west, where the burning of the bed
is disclosed by the smoke and fumes that rise from it
and by the heat at the surface of the earth near the
outcrop or above the bed—heat so intense that it kills
all vegetation. As the coal burns out, the overlying
rock or earth generally caves in so as to form large
fissures in the ground. As the burning works back
from the outcrop, the heat acts on the overlying rocks,
but finally combustion is smothered for the lack of
oxygen. It is difficult to say how far back from the
outcrop the burning may extend. Field studies made
by the United States Geological Survey, Department of
the Interior, indicate that a bed lying beneath 20 ft. or
less of cover may burn out completely under large
areas, and even where the cover is several hundred feet
thick the burning may extend 500 ft. back from the
outcrop.

A brief account by G. S. Rogers of the burning of
coal beds in place, with a discussion of the causes and a
petrologic and chemical description of some of the baked
and fused rock formed, has also been published by
the United States Geological Survey as Professional
Paper 108—A.

Zirconia Crucibles.

The possibilities of zirconia as refractory material
have been much urged of late, and expei imenting with
zirconia is going on in various quarters. The account
of the recent continued work of Prof. O. Ruff and his
collaborators at Danzig (Zeitsehrift fur anorganische
Chemie, abstracted in Engineering) is encouraging.
The new crucibles made of zirconia, with small
additions of other oxides, could be r temperatures of
2,200 and even 2,400 degs. Cent. But there are
difficulties caused by the affinity of zirconia for carbon
and by other factors, and the temperature at which the
zirconia bad been baked proved to be a factor of con-
siderable influence. In their new researches, Ruff and
G. Lauschke had at disposal a crude zirconia (83 5 per
cent, of Zr2O3, 11'5 SiO2, 4’6 Fe2O3) and a purified
zirconia (98’75 Zr„O3. 0'95 SiO2, 0’27 Fe2O3). Various
samples of the latter had been baked at five tempera-
tures, ranging from 750 to 1,400 degs. Cent., and these
samples, ranging in density from 5’7 down to 4’99, were
kept separate during the expei iments. Small cylinders
were prepared by mixing the zirconia with water (9 or
10 per cent.), and sometimes also with 1 per cent, starch.
Melting-pointde’.erminationsof the materials were made
in the Ruff vacuum electric carbon tube furnace, at
pressures from 5 mm. of mercury upward, sometimes in
a hydrogen atmosphere. The following temperatures
indicate visible melting of the cylinders:—Zirconia,
2,563 degs. Cent —this point was the same for all the
samples, also in hydrogen at low pressures, a high
hydrogen pressure lowered the melting-point; silica,
SiO2, 1,850 (fused to a white bead); glucina (beryllium
oxide BeO), 2,410 (no vapours ; this point is lower- than
that previously found by Ruff) ; magnesia could not be
melted, it evaporated completely when heated above
2,000 to 2,690 degs.; A1.2O3, 2,005 to 2,008 (very little
vapour); thoria, ThO.2 gave white mists above 2,400,
but was not melted at 2,780 (formerly melted at 2,425 or
2,470); yttria, Y2O3, 2,410 (vapours above 2,350) degs.
The addition of any of these oxides to zirconia lowered
the melting-point, but raised it in the case of ThO2 and
Y2O3. Crucibles were then made of zirconia, to which
1, 3, or 6 per cent, of the other oxides were added, the
mixture containing also water and starch, as stated.
The crucibles were straight cylinders, 45 or 30 mm.
high, 28 or 15 mm. external diameter, and 3 or 1’5 mm.
wall thickness. They were baked in a Hessian crucible,
and then heated in the electric furnace for 70 minutes
up to 2,400 degs. maximum. In strength the soft and
baked zirconia crucibles resembled clay. To reduce the
formation of carbide, the crucibles were placed within
covered crucibles of crude zirconia, which suffered in
their turn; some oxides, volatilised from the outer
crucible, then condensed on the inner. During the
baking the crucibles altered their shape slightly ; they
became coloured (yellow, green, reddish, blue, grey.
sometimes mottled), turned crystalline, increased in
strength (especially if previously baked at low
temperature), and lost up to 20 per cent, in weight
(moisture, chemical reduction, volatilisation), but. on
the other hand, gained in weight by the condensation
aforesaid. There was also shrinkage, and the porosity
increased, owing to the volatilisation, especially of the
added oxides. The porosity was determined by
evacuating the pores and then letting water soak into
them ; the deduced porosities, 4 to 39 per cent., were
probably too high. This treatment was followed by
heating the crucibles in the oxidising blowpipe flame,
when the colour turned yellow-red (iron oxide). Many
of the crucibles crumbled in this flame, because the
carbides and lower oxides formed in the reducing
atmosphere of the carbon furnace weie reoxidised;
those baked at 2,000 degs. stood the oxidation better
than those baked at 2,400, and the crucibles containing
6 per cent, of alumina proved strongest. The surviving
crucibles were finally heated to the highest tempera-

tures in the electric furnace and then analysed. The
conclusion is that the addition of oxides to be made
sho/uld depend upon the temperature at which the
zirfconia is to be baked: if at 2,000 degs. add 1 per cent,
of alumina; if at 2,200,1 percent, of thoria; if at2,400,
1 to 3 per cent, of yttria. Higher percentages would
only increase the porosity; glucina, magnesia and silica
are not recommendable, as too volatile or for other
reasons.

been modified. This tube A is

I

"WAI

i-:,’ dflr

• ■■

A/ - t vZr*' s'

THE DAVIS-BRIGGS OXYMETER LAMP.

Messrs. John Davis and Son (Derby) Limited, have
afforded us the opportunity of examining one of the
latest models of the Oxymeter safety lamp, of which
they are the sole makers. Dr. Henry Briggs, of Edin-
burgh. the inventor, described the lamp at length before
the Mining Institute of Scotland (see Colliery Guardian,
February 25, 1916, p. 359) ; but since writing that
paper, Dr. Briggs has made further improvements
that are embodied in the lamp now under consideration,
which has been tested at Eskmeals, and “ recommended
for approval.”

Dr. Briggs’ purpose is to put in the bands of the
mine official a safety lamp which will enable him to
test, with sufficient accuracy for ordinary purposes, for
both firedamp and oxygen—the former by the “ blue
cap ” method (improved, if preferred, by the use of the
well-known Briggs loop), and the latter by the special
lamp-fitting described below. So far as we are aware,
the Oxymeter lamp is the only contrivance—short of
fragile gas analysis apparatus—which permits of mine
ail’ being tested for both these gases ; and, with this
lamp, the deputy or the fireman will, for the first time,
be able to make sure that the air complies as to purity
with all the ventilation standards prescribed in the Coal
Mines Act.

The accompanying illustration shows the latest and
most practical form of the device adapted to the
A.H.G. lamp. It will be observed that one of the four
upright inlet tubes
cut off 1A in. above
the lamp base, and
is given an exter-
nal screw thread,
on which travels
a hollow screw-
thimble B. A
solid rod C, of a
diameter slightly
less than the bore
of A, is fitted so
that its lower
extremity (which
is pointed) is at
the same level as
the top of A. The
other three inlet
tubes. are stopped
at their upper ends,
but one has a side
opening D. Nor-
mally, the lamp
takes its air supply
partly through D
and partly down
A, the thimbletlien
being at the bottom
of its run so as to
impede the air
stream as little as
possible.

When it is de-

sired to test for oxygen or blackdamp, the operator
coiers the hole D with his thumb, after reducing the
flame to about half working size. He then turns the
thimble to make it advance up the screw. This has
the effect of lengthening the inlet passage, and increasing
the friction impeding the ingoing air. In due course,
all white light disappears from the flame. The thimble
is now turned more slowly until quivering is noticed in
the flame, whereupon the hole D is at once uncovered.
The flame revives, and after it has been raised to normal
height, the position of the thimble is read against the
scale on the brass strip E, both sides of which are
graduated. The reading gives the percentage of oxygen
present, the graduationslanging from.16 to 21.

In the lamp illustrated, the top of the milled portion
of the thimble serves as a reading index. A recent
improvement consists in providing a scale of blackdamp
percentages under the oxi gen scale; and now the top
of the thimble reads off the oxygen figure, and the
bottom of the thimble the equivalent blackdamp pro-
portion.

As some misapprehension still exists, it is as well to
note that by “ blackdamp ” is meant nitrogen plus
carbon dioxide, and not merely the latter gas. The
“ blackdamp ” here referred to is the whole of the ex-
tinctive gas. or mixture of gaces, polluting the air. In
British coal mines that mixture invariably contains
considerably more nitrogen than carbon dioxide.

Another point woithy of remark is that the lamp
automatically takes into account the watery vapour
always present to a considerable amount in mine air.
This vapour occupies a definite volumetric proportion
depending on temperature and degree of saturation,
and Dr. Briggs holds that it is as incorrect to neglect it
(as is done in ordinary analysis) as to disregard the
presence of any other constituent of the air. The
lamp, in other words, gives the oxygen percentage
actually existing, and not that which would exist had
the air been dry.

Humidity has an important influence on a flame,
especially with hot saturated air. So marked does this
influence become that, if the lamp is intended to be used
in an underground district whose temperature exceeds
70 degs. Fahr., it is advisable to have the scale calibrated
accordingly. The scale as ordinarily supplied is
sufficiently exact for practical purposes for temperatures
up to 70 degs.

Firedamp, if present in such an amount as to make
a visible cap on the lowered flame, causes the oxygen