560

THE COLLIERY GUARDIAN,

March ’24, 1916.

CURRENT SCIENCE

Problems of Domestic Heating.

Mr. A. H. Barker, in a recent issue of Nature, dis-
cusses the efficiency of different methods of heating—a
problem very difficult to solve on a purely scientific
basis. It is, indeed, difficult to attach a precise mean-
ing to the expression “ efficiency ” in connection with
heating apparatus. The word as commonly understood
in connection with devices for the utilisation of energy
in any form, means the ratio of the total amount of
energy utilised to that consumed. In a heating
apparatus it is difficult to say what fraction of the
energy is to be regarded as “utilised.”

As a rough practical basis of comparison between
different systems of heating, we may take the relative
amounts of energy necessary to be employed, in a room
in order to produce the same feeling of warmth as
measured by a suitably calibrated instrument (not a
thermometer), while maintaining approximately the
same interchange of air.

The subjoined table is based on direct experiment in
this sense, and refers to the cost of continuous uniform
heating in certain natural or normal conditions, the full
description of which would occupy much space. An
alteration of the conditions would undoubtedly alter the
percentages given.. These values cannot, however, in
any event be taken as the practical relative costs,
because of the manner in which the respective methods
of heating are commonly employed in practice. A hot
water heater or anthracite stove is generally burning all
the day and frequently at night. A gas fire or electrical
stove is usually turned oh when the occupant leaves
the room. There is a wide difference between this and
the maintenance of a continuous temperature through-
out the room, and a set comparison between the “ cost
efficiency ” is therefore misleading. It is probable, for
instance, that in certain circumstances a good gas stove
is a cheaper .method of heating an occasionally used room
than is an anthracite stove, although the cost efficiency of
the latter is far below (i.e., more economical than) the
former.

In order to enable, the running cost to. be calculated
at different prices of the fuel (including in that term
electrical power), it will bo desirable to quote the rela-
tive equivalents of different agents, as compared with
1,000 Board of Trade units of electrical energy.

Table of Efficiencies for Continuous Heating.

The rates given are those current in London previous
to the war and at present :—

Approximate equivalents.

Rates
per
unit.

Gross
cost.
£

1,000

Electric Radiator.

Board of Traded
emits of elec- cenk
trical energy
utilised in best

< radiant stove }> 100
of 69 °/_ radiant I
efficiency dis- I
posed in the |
best manner J

l^d..

3d. .

5d. .

6d. .

. 6'25 ... 100

.12-5 ...200

.20*8 ...335

.25	...400

Open Fire.

1*38 tons of f	"|

best house | Burnt in bad |
coal, 14,000 <( grate unsuit-
B.T.U. per | ably disposed |
lb. L	J

0-520 ton best fBurnt in best l
house coal,

14,000	1 Ope'1

B.T.U. per|
lb.	i wal1

8 I

26/-.

35/-.

1-8 ... 29

2’42 ... 39

modern

sunk in

J

21

26/-

' 35/-

0-675...10’8

0-91 ...146

Closed Anthracite Stove.

0*235 ton best f Burnt in best)
anthracite, |	modern slow |	rm/

14,500	combustion, f 45	} ■-J,'

B.T.U. per |	closed anthra- |	•'

lb.	cite stove J

0-47 .7’54

0-59 ...9-42

Gas Stove.

18,300 cu. ft. f Burnt in medium"
gas, at 520 J old - fashioned
B.T.U. per*] gas fire (not
cu. ft. L worst type)

10,700 cu. ft. f Burnt in best^
gas, 520]	modern ven- I

B.T.U. per ]	tilating	gas [

cu. ft.	stove	J

36

62

C 2'6 ... 2*29 ...36*6

I 3/- ... 2'75 ...44

I 2/6 ... 1*34 ...21-3

I 3/- ... 1*60 ...25*6

0*198 ton of
coke, 12,500
B.T.U. per
lb.

0'306 ton of
coke, 12,500

B.T.U. per |

lb.	I

Water Radiators.

" Burnt in best pro-"
vided modern
water boiler
with well- >
clothed circu-
lation to radia-

L tors or pipes

"In usual small"]
house hotl
water instal- (

]	1 a t i on

| generally
L stalled

as [
in- |

62

40

Oil Stove.

( 20/-... 0-198...3*17

I 30/-... 0-297...475

( 20/- . 0-306...4-9

t 30/- .. 0'459...7*36

19’5 gals, f
petroleum |
0*87 gravity, J
20,240

B.T.U. per j
lb.	L

("Completely")
|	burnt in any	|

J	kind of stove	I

)	discharging	;

products into	/

air of room J

I 8d. ... 0-650...10-4
llOd. ... 0-810...13-0

AND TECHNOLOGY.

Calculation of Mine Timbers.

Some useful rules for calculating the dimensions of
mine timbers are given by A. G. Morlock in Coal Age.
When the diameter and length of an existing collar are
known, the safe load per foot of length that it will
support may be calculated by the formula—■

w = 0-065 f &	(1)

in which

w = Safe load per foot of length of span (lb.);

d = Least diameter of collar (in.);

Z = Length of clear span (ft.);

/=Safc unit fibre stress (1,2001b. per sq. in. of
section, for long leaf yellow pine and white oak,
and 9001b. per sq. in. for short leaf yellow
pine).

In calculating legs for compressive stresses only, the
formula—■

f __ L/700 4- 15c + c2)
Je a (700 + 15c)

should be used, in which

L = Total load on leg (lb.):

a = Area of cross section of leg (sq. in.);

c = Length of leg in inches, divided by its least
diameter in inches.

The diameter of the leg must be assumed for trial,
the most economical section being that in which the
safe unit fibre stress is not exceeded.

When calculating beams of special cross section, as
steel I-beams, it is customary to .employ an expression
called the “ section modulus ” of the beam. The
section modulus (S) of a beam is a value that, multiplied
by the. unit fibre stress (/) of tire material, gives the
bending moment (Al) which such beam is capable of
supporting, as expressed by the formula—

M =/S	(3)

But, for a beam uniformly loaded and supported at
each end, the bending moment (Al), in inch-pounds, is—

M = LyL2 = 1-5 wV	(4) '

o

Combining equations 3 and 4 gives for the section
modulus—

s = i-snp	(5)

Atmospheric Pollution.

Bather late in the day the first report of the Committee
on the Investigation of Atmospheric Pollution has just
appeared. The report covers the year ended March 1915,
and may be regarded as the firstfruit of the conference
of delegates of municipal authorities and others, held in
connection with the Smoke Abatement Exhibition of
1912, in London. A committee was then appointed, of
which Sir Napier Shaw, F.R.S., Director of the Meteoro-
logical .Office, is chairman, and Dr. J. S. Owens honorary
secretary. Stations for conducting systematic observa-
tions are spread over the country, and these stations—■
39 at present—have for some time been publishing
monthly reports.

The present investigation aims at, in the first instance,
ascertaining the amount and the composition of the
matter which is suspended in the air. Various methods
are resorted to for this purpose. The simplest and most
largely used by the Committee is to collect, measure,
and analyse all the matter caught in a gauge vessel of
4 sq. ft. catchment area. A convenient method for a
rapid determination of the solid matter in suspension in
tbe air is that of J. S. Owens, in which the air is drawn
through filter paper, and the amount of discoloration
produced is determined.

The quantitative results, tabulated and grouped by the
Committee, with the help of the “ correspondents and
analysts ” at the various stations, rely on the standard
gauge measurements, analysed and referred to unit areas
on a uniform plan. The analysis determines (1) tarry or'
other carbon .compounds soluble in carbon bisulphide,
mainly due to imperfect combustion of coal and wood,
and recently also to the practice of tarring roads; (2)
carbonaceous matter not soluble in CS2, i.e., coal dust
and unburnt coal, animal and vegetable matter and
refuse; (3) insoluble ash, including dust from roads; (4)
loss on ignition, i.e., the volatile and combustible parts
(largely organic) of the compounds dissolved in the rain
water; and (5) the residual ash after ignition, contain-
ing, like (4), acids and salts dissolved in the rain water,
and partly included in the combustion products of coal.
These five items make up (6) the total solids collected in
the gauge. Separate estimates are made (7) of the
sulphates as S04, (8) of the chlorides as Cl (partly salt-
water spray); and (9) of the ammonia (from the destruc-
tive distillation of coal and decay of animal refuse). The
totals (6) are calculated in metric tons per sq. kilom.,
one ton (of 2,205 lb.) per sq. kilom. beipg equivalent to-
ff lb. per acre. In making these estimates, some cor-
rection had to be effected, since the gauges of normally
4 ft. square are not exactly of that area; high accuracy
is, of course, not required. The actual rainfall is inde-
pendently recorded. For the better classification of the
results, a further subdivision of the figures into classes
A, B, C, D has been adopted, based upon arbitrary units
of deposits. The unit, for total solids is five tons per
month. When a station belongs to class A, the total
amount of solids found per month per sq. kilom. is less
than five tons; when it belongs to class B, less than 15
tons (three units); when to class C, less than 25 tons
(five units); and when to class D, the total amount of
solids exceeds 25 tons per month. The other units are :
Tar, 0-05 ton; other carbonaceous matter, 1-ton; ash,
2 tons; loss on ignition, 0-75 ton; residual ash, 1-5 tons;
sulphuric acid, 1 ton; chlorine, 0-5 ton; and ammonia,.
0-05 ton.

When the results are grouped in this way, we find that
different stations of the same and of different towns not
rarely differ to a surprising degree. A station may belong
to class A in one respect, and to C or D in others. Even
tar and other carbonaceous matters do not by any means
always go together, nor do the total solids and the rain-
fall. The highest tar value of 0-37 (all in tons per
sq. kilom. per month) has been observed in Oldham; the
lowest in Malvern, which is a clean air town of the A
type in all respects; Bowdon (Manchester) is also good
as to tar (0*01); Liverpool and Stirling are bad, next to
Oldham. Oldham has also the highest carbonaceous
matter figure (7-09); whilst Bowdon and Birmingham
South-West are fairly low. Again, Oldham leads as to
insoluble ash (16-21).

MIDLAND INSTITUTE OF MINING, CIVIL
AND MECHANICAL ENGINEERS.

A meeting oi the Midland Institute of Alining, Civil
and Mechanical Engineers was held at the Queen’s
Hotel, Leeds, on :Tuesday, March 21, under the chair-
manship of Air. Thomas Beach.

The chairman announced the following elections:—
Afember, Air. Robert Etherington Dobin son, 224,
Sheffield-road, Barnsley; associate member, Air. Geoffrey
Edwin Foxwell, 10, Violet Bank-road, Nether Edge,
Sheffield.

The chairman read a letter from the secretary of the
Institution of Alining Engineers to Air. G. Blake Walker,
saying : “I have much pleasure in advising you that
I forwarded the other day a cheque for £713 3s. 4d. to
Air. A. Denny Bayley, as -the contribution of this
institution towards the transport of the wounded fund for
the British Red Cross Society. In acknowledging the
receipt of the cheque, All’. Bailey writes me- as under :
‘ I shall be much obliged if you will be good enough
to convey to the members of the various societies my
best thanks, together with those of the joint war com-
mittee of the British Red Cross and Order of St. John
for this generous contribution, which is greatly appre-
ciated.’ I may, in addition to that, inform you that the
amount subscribed by the Alidland Institute was
.£319 15s.” The chairman remarked that there was
nothing for the Alidland Institute to be ashamed of in
that.

Dr. Percy Groom, Professor of the Technology of.
Woods and Fibres!at the Imperial College, London, read
a paper on “ Pit Timber and its Preservation,” which
will be found on page 554.

Discussion.

The Chairman said there was no doubt that a very
great deal might be done in preserving timber under-
ground, but he did not think that that applied very much
to the majority of .the pits in that district, because the
timber in them got broken before it had a chance to get
decayed. In some of the shallower mines, however,
where timber would stand for years, he had no doubt
that very great economies could be brought about by
some method of dealing with the fungi in the manner
indicated by the author of the paper.

Prof. AV. G. Fearnsides (Sheffield University) said
he thought the paper had originated ' from something
which he said to Prof. Groom some time ago. Since the
war began, it had been his duty to visit a great many-
pits, not particularly those that were winning coal, but
those that were winning fireclay and ganister. Alost of
them were not very distant from Leeds, or from Shef-
field. Almost every time one went into these shallow
mines, one found the place littered with fungi, gener-
ally in course of fructification. He went as a geologist,
and was not particularly concerned with this matter,
but it occurred to him that, where he saw these fungi
fructifying and spreading their seeds about, it would be
worth while if something could be done. He had made
some enquiries, and had sent Prof. Groom some props,
which one of the managers was good enough to get out
for him. It struck him that the difference in the
behaviour of the timber in the fresh air and in the returns
was very notable. One could see, on that side which
was meeting the air, that generally the fungi were
beginning their attack, whilst on the other side, remote
from the current which brought the seeds, the timber
lasted a good deal longer. He saw this, not only in
one mine, but in almost all, that it was his duty to go
into, which were working under quite wet and shallow
conditions. In those places it seemed to him that the
weights the timber was expected to carry were not so
great as in other places, and yet the timber was standing
exceedingly badly. The number of cases that he saw
was by no means negligible, and it seemed to him that
if anything could be done for even those shallow mines
to prevent the onset of this disease, quite a lot of timber
would be saved in that coal field. He hoped that the
matter would be taken up. It was evidently a difficult
question, and there were more conditions than met the
eye. The acidity of the water which one sometimes
found in the pits seemed to have something to do with
it. Lie thought, also, that the temperature and
humidity of the mines-should be studied alongside the
investigations from the botanical point of view.

Air. AV. D. Lloyd (Altofts) said he had no -wish to
obstruct any enquiry which would help to decrease the
cost of timber in mines, but, at the same time, so far
as the deeper pits were concerned, he thought the paper