Scientific American Supplement, No. 303
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Various >> Scientific American Supplement, No. 303
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This gives very important economical results; for if the cost of the
Dowson gas given in the tables as 41/4d., 3-1/3d., and 23/4d. per 1,000
cubic feet, be multiplied by 5 there will be 1s. 91/4d., 1s. 43/4d., and 1s.
23/4d., or a mean of 1s. 51/2d. for the equivalent of 1,000 cubic feet of
coal gas, which usually costs from 3s. to 4s., and this represents an
actual saving of about 50 to 60 per cent, in working cost. Another
practical consideration is that coal gas requires 224 lb. to 250 lb. of
coal per 1,000 cubic feet of gas, but the writer requires only 12 lb.
per 1,000 cubic feet, and multiplying this by 5 to give the equivalent
of 1,000 cubic feet of coal gas, for engine work, there are 60 lb.
instead of 224 lb. to 250 lb. This is only 24 to 27 per cent, of the
weight of the coal required for coal gas, and in many outlying districts
this will effect an appreciable saving in the cost of transport.
APPENDIX.
TABLE I.
_Generator A Size_ (producing 1,000 cubic feet per hour):
Anthracite to make gas at the rate of 1,000 s. d.
cubic feet per hour=l2 lb x 9 working
hours=l08 lb., or say, 1 cwt. at 20s. a
ton.................................... 1 0
Allowance for wages of attendant......... 1 0
Repairs and depreciation of generator,
gasholder, etc. (5 per cent. on Ll25)=
per working day........................ 0 5
Interest on capital outlay, ditto........ 0 5
______
Total........................... 2 10
cub. ft.
Gas produced............................. 9.000
Less gas used for generating and
superheating steam..................... 1,000
_____
Total effective gas for 2s. 10d. 8,000
Net cost 41/4 d. per 1,000 cubic feet.
TABLE II.
_Generator B Size_ (producing 1,500 cubic feet per hour)
Anthracite to make gas at the rate of 1,500 s. d.
cubic feet per hour=18 lb. x 9 working
hours=162 lb., or, say, 11/2 cwt. 20s.
a ton.................................. 1 6
Allowance for wages of attendant......... 1 0
Repairs and depreciation of generator,
gasholder, etc. (5 per cent, on L140)
=per working day....................... 0 51/2
Interest on capital outlay, ditto........ 0 51/2
___ ___
Total........................... 3 5
cub. ft.
Gas produced............................. 13,500
Less gas used for generating and
superheating steam..................... 1,200
______
Total effective gas for 3s. 5d.. 12,300
Net cost 3 1/3d. per 1,000 cubic feet.
TABLE III.
_Generator C Size_ (producing 2,500 cubic feet per hour):
Anthracite to make gas at the rate of 2,500 s. d.
cubic feet per hour=30 lb. x 9 working
hours=270 lb. at 20s. a ton............ 2 41/2
Allowance for wages of attendant....... 1 6
Repairs and depreciation of generator,
gasholder, etc. (5 per cent, on L160)=
per working day...................... 0 61/2
Interest on capital outlay, ditto...... 0 61/2
_______
Total......................... 4 111/2
cub. ft.
Gas produced........................... 22,500
Less gas used for generating and
superheating steam................... 1,500
______
Total effective gas for 4s. 111/2d 21,000
Net cost, say, 23/4 d. per 1,000 cubic feet.
* * * * *
ON THE FLUID DENSITY OF CERTAIN METALS.
[Footnote: Abstract of paper read before Section C (Chemical Science),
British Association meeting, York.]
By PROFESSOR W. CHANDLER ROBERTS, F.R.S., and T. WRIGHTSON.
The authors described their experiments on the fluid density of metals
made in continuation of those submitted to Section B at the Swansea
meeting of the Association. Some time since one of the authors gave an
account of the results of experiments made to determine the density of
metallic silver, and of certain alloys of silver and copper when in a
molten state. The method adopted was that devised by Mr. R. Mallet, and
the details were as follows: A conical vessel of best thin Lowmoor plate
(1 millimeter thick), about 16 centimeters in height, and having an
internal volume of about 540 cubic centimeters, was weighed, first
empty, and subsequently when filled with distilled water at a known
temperature. The necessary data were thus afforded for accurately
determining its capacity at the temperature of the air. Molten silver
was then poured into it, the temperature at the time of pouring being
ascertained by the calorimetric method. The precautions, as regards
filling, pointed out by Mr. Mallet, were adopted; and as soon as the
metal was quite cold, the cone with its contents was again weighed.
Experiments were also made on the density of fluid bismuth; and two
distinctive determinations gave the following results:
10.005 )
) mean 10.039.
10.072 )
The invention of the oncosimeter, which was described by one of the
authors in the "Journal of the Iron and Steel Institute" (No. II.,
1879, p. 418), appeared to afford an opportunity for resuming the
investigation on a new basis, more especially as the delicacy of the
instrument had already been proved by experiments on a considerable
scale for determining the density of fluid cast iron. The following is
the principle on which this instrument acts:
If a spherical ball of any metal be plunged below the surface of a
molten bath of the same or another metal, the cold ball will displace
its own volume of molten metal. If the densities of the cold and molten
metal be the same, there will be equilibrium, and no floating or sinking
effect will be exhibited. If the density of the cold be greater than
that of the molten metal, there will be a sinking effect, and if less a
floating effect when first immersed. As the temperature of the submerged
ball rises, the volume of the displaced liquid will increase or decrease
according as the ball expands or contracts. In order to register these
changes the ball is hung on a spiral spring, and the slightest change in
buoyancy causes an elongation or contraction of this spring which can
be read off on a scale of ounces, and is recorded by a pencil on a
revolving drum. A diagram is thus traced out, the ordinates of which
represent increments of volume, or, in other words, of weight of fluid
displaced--the zero line, or line corresponding to a ball in a liquid of
equal density, being previously traced out by revolving the drum without
attaching the ball of metal itself to the spring, but with all other
auxiliary attachments. By means of a simple adjustment the ball is kept
constantly depressed to the same extent below the surface of the liquid;
and the ordinate of this pencil line, measuring from the line of
equilibrium, thus gives an exact measure of the floating or sinking
effect at every stage of temperature, from the cold solid to the state
when the ball begins to melt.
If the weight and specific gravity of the ball be taken when cold,
there are obtained, with the ordinate on the diagram at the moment of
immersion, sufficient data for determining the density of the fluid
metal; for
W / W1 = D / D1
the volumes being equal. And remembering that
W (weight of liquid) = W1 (weight of ball) + x
(where x is always measured as +_ve_ or -_ve_ floating effect), there is
obtained the equation:
D1 x ( W1 + x)
D = --------------- .
W1
[TEX: D = \frac{D_1 \times (W_1 +x)}{W_1}]
The results obtained with metallic silver are perhaps the most
interesting, mainly from the fact that the metal melts at a higher
temperature, which was determined with great care by the illustrious
physicist and metallurgist, the late Henri St. Claire Deville, whose
latest experiments led him to fix the melting point at 940 deg. Cent. The
authors of the paper showed that the density of the fluid metal was 9.51
as compared with 10.57, the density of the solid metal. Taking their
results generally, it is found that the change of volume of the
following metals in passing from the solid to the liquid state may be
thus stated:
Specific Specific
Metal. Gravity, Gravity, Percentage of
Solid. Liquid. Change.
Bismuth 9.82 10.055 Decrease of volume 2.3
Copper 8.8 8.217 Increase " 7.1
Lead 11.4 10.37 " " 9.93
Tin. 7.5 7.025 " " 6.76
Zinc 7.2 6.48 " " 11.10
Silver 10.57 9.51 " " 11.20
Iron 6.95 6.88 " " 1.02
* * * * *
HYDROPHOBIA PREVENTED BY VACCINATION.
M. Pasteur and other French savants have lately been devoting special
attention to hydrophobia. The great authority on germs has, in fact,
definitely announced that he does not intend to rest until he has made
known the exact nature and life-history of this terrible disease, and
discovered a means of preventing or curing it. The most curious result
yet attained in this direction, however, has been announced by Professor
V. Galtier, of the Lyons Veterinary School. This inquirer has found, in
the first place, that if the virus of rabies be injected into the veins
of a sheep, the animal does not subsequently exhibit any symptoms of
hydrophobia. This in itself would be a sufficiently curious result
to justify attention, though its importance, except as confirmatory
testimony, becomes less striking when it is remembered that M. Pasteur
has lately shown that the special _nidus_ of the disease appears to be
the nervous tissue, and particularly the ganglionic centers. But there
is this further curious consequence: sheep who have thus been treated
through the blood, and who are afterwards inoculated in the ordinary
way through the cellular tissue, as if by a bite, are proof against
the disease. It is as though the injection into the veins acted as a
vaccine. Twenty sheep were experimented upon; ten only were treated to
the venous injection, and then all were inoculated through the cellular
tissue. The ten which had been first "vaccinated" continue alive and
well; they have not even shown any adverse symptoms. The other ten have
all died of rabies. It remains to say why M. Galtier experimented
upon sheep, and not upon dogs and cats, which usually communicate the
disease. The incubation of the disease is much more rapid and less
capricious in the sheep than in the dog or in man, and hence M. Galtier
was able to get his results more certainly within a short period. Having
succeeded so far, he is now justified in undertaking the more protracted
series of observations which experiments upon the canine species will
involve; and this he proposes to do. Experiments of this nature are not
without a serious risk, and admiration is almost equally due to the
courage and the intelligence of the experimentalist. But what will the
anti-vaccinator say?--_Pall Mall Gazette_.
* * * * *
ON DIPTERA AS SPREADERS OF DISEASE.
By J.W. SLATER.
The two-winged flies, in their behavior to man, stand in a marked
contrast to all the other orders of insects. The Lepidoptera, the
Coleoptera, the Neuroptera, the Hymenoptera no doubt occasion, in some
of their forms at least, much damage to our crops. But none of them are
parasitic in or upon our bodies; none of them persistently intrude into
our dwellings, hover around us in our walks, and harass us with noise
and constant attempts to bite, or at least to crawl upon us. Even the
ants, except in a few tropical districts, rarely act upon the offensive.
The Hemiptera contain one semi-parasitic species which has attained a
"world-wide circulation," and one degraded, purely parasitic group.
But the Diptera, among which the fleas are now generally included as a
degenerated type, comprise more forms personally annoying to man than
all the remaining insect orders put together. These hostile species are,
further, incalculably numerous, and occur in every part of the globe.
Mosquitoes swarm not merely in the swampy forests of the Orinoco or the
Irrawaddy, but in the Tundras of Siberia, en the storm-beaten rocks of
the Loffodens, and are even encountered by voyagers in quest of the
North Pole. The common house fly was probably at one time peculiar to
the Eastern Continent, but it followed the footsteps of the Pilgrim
Fathers, and is now as great a nuisance in the United Slates and the
Dominion as in any part of Europe. It is curious, but distressing, to
note the tendency of evils to become international. We have communicated
to America the house-fly and the Hessian fly, the "cabbage-white,"
the small pox, and the cholera. She, in return, has given us the
_Phylloxera_, a few visitations of yellow fever, the _Blatta gigantea_,
and, climate allowing, may perhaps throw in the Colorado beetle as a
make-weight. In this department, at least, free trade reigns undisputed.
It is a singular thing that no beautiful, useful, or even harmless
species of bird or insect seems capable of acclimatizing itself as do
those characterized by ugliness and noisomeness.
But, returning from this digression, we find in the Diptera the habit of
obtrusion and intrusion, of coming in actual contact with our food and
our persons, combined with another propensity--that of feeding upon
carrion, excrement, blood, pus, and morbid matter of all kinds. This
is a combination far more serious than is generally imagined. If the
fly--which may at any moment settle upon our lips, our eyes, or upon
an abraded part of our skin--were cleanly in its habits, we need feel
little annoyance at its visits. Or if it were the most eager carrion
devourer, but did not, after having dined, think it necessary to
seek our company, we might hold it, as is done too hastily by some
naturalists, a valuable scavenger. I fear, however, that I have already
made too great a concession. So long as very many persons are suffering
from disease--so long as many diseases are capable of being transmitted
from the sick to the healthy--so long must any creature which is in the
habit of flying about, and touching first one person and then another,
be a possible medium of infection and death.
Let us take the following case, by no means imaginary, but a
generalization from occurrences far too frequent: A healthy man, sitting
in his house or walking in the fields, especially in countries where the
insectivorous birds have been shot down, suddenly feels a sharp prick on
his neck or his cheek. Putting his hand to the place he perhaps crushes,
perhaps merely brushes away, a fly which has bitten him so as to draw
blood. The man thinks little of so trifling a hurt, but the next morning
he finds the puncture exceedingly painful. An inflamed pimple forms,
which quickly gets worse, while constitutional symptoms of a feverish
kind come on. In alarm he seeks medical advice. The doctor tells him
that it is a malignant pustule, and takes at once the most active
measures. In spite of all possible skill and care the patient too often
succumbs to the bite of a _mouche charbonneuse_, or carbuncle-fly. But
has any kind of fly the property of producing malignant pustule by
some specific inherent power of its own? Surely not. The antecedent
circumstances are these: A sheep or heifer is attacked with the disease
known in France as _charbon_, in Germany as _milz-brand_, and in England
as _splenic fever_. Its blood on examination would be found plentifully
peopled with bacteria. If a lancet were plunged into the body of the
animal, and were then used to slightly scratch or cut the skin of a man,
he would be inoculated with "charbon." The bite of the fly is precisely
similar in its action. Its rostrum has been smeared with the poisoned
blood, an infinitesimal particle of which is sufficient to inclose
several of the disease "germs," and these are then transferred to the
blood of the next man or animal which the fly happens to bite. The
disease is reproduced as simply and certainly as the spores of some
species of fern give rise to their like if scattered upon soil suitable
for their growth. But flies which do not bite may transfer infection.
Every one must know that if blood be spilt upon the ground a crowd of
flies will settle upon and eagerly absorb it. Animals suffering from
splenic fever in the later stages of the disease sometimes emit bloody
urine. Often they are shot or slaughtered by way of stamping out the
plague, and their carcasses are buried deep in the ground. But some loss
of blood is sure to happen, and this will mostly be left to soak into
the ground. Here again the flies will come, and their feet and mouth
will become charged with the contagion. Such a fly, settling upon
another animal or a man, and selecting--as it will do by preference, if
such exist--a wound, or a place where the skin is broken, will convey
the disease.
Again, M. Pasteur has thoughtfully pointed out that if an animal has
died of splenic fever, and has been carefully buried, the earth-worms
may bring up portions of infectious matter to the surface, so that sheep
grazing, or merely being folded over the spot in question, may take the
plague and die. Hence be wisely counsels that the bodies of such animals
should be buried in sandy or calcareous soils where earth-worms are not
numerous. But it is perfectly legitimate to go a step farther. If such
worm-borings retain the slightest savor of animal matter, flies will
settle upon them and will convey the infectious dust to the most
unexpected places, giving wings to the plague.
Now it is very true that no one has seen a fly feasting upon the blood
of a heifer or sheep dying or just dead of splenic fever, has then
watched it settle upon and bite some person, and has traced the
following stages of the disease. But it is positively known that a
person has been bitten by a fly, and has then exhibited all the symptoms
of charbon, the place of the bite being the primary seat of the
infection. We know also, beyond all doubt, the eagerness with which
flies will suck up blood, and we likewise know the strange persistence
of the disease "germs."
Again, the avidity of flies for purulent matter is not a thing of mere
possibility. In Egypt, where ophthalmia is common, and where the "plague
of flies" seems never to have been removed, it is reported as almost
impossible to keep these insects away from the eyes of the sufferers.
The infection which they thus take up they convey to the eyes of persons
still healthy, and thus the scourge is continually multiplied.
A third case which seems established beyond question is the agency of
mosquitoes in spreading elephantiasis. These so-called sanitary agents
suck from the blood of one person the Filariae, the direct cause of the
disease, and transfer them to another. The manner in which this process
is effected will appear simple enough if we reflect that the mosquito
begins operations by injecting a few drops of fluid into its victim, so
as to dilute the blood and make it easier to be sucked.
So much being established it becomes in the highest degree probable that
every infectious disease may be, and actually is, at times propagated
by the agency of flies. Attention turned to this much neglected quarter
will very probably go far to explain obscure phenomena connected with
the distribution of epidemics and their sudden outbreaks in unexpected
quarters. I have seen it stated that in former outbreaks of pestilence
flies were remarkably numerous, and although mediaeval observations on
Entomology are not to be taken without a grain of salt, the tradition
is suggestive. Perhaps the Diptera have their seasons of unusual
multiplication and emigration. A wave of the common flea appears to have
passed over Maidstone in August, 1880.
We now see the way to some practical conclusions not without importance.
Recognizing a very considerable part of the order of Diptera, or
two-winged flies, as agents in spreading disease, it surely follows
that man should wage war against them in a much more systematic and
consistent manner than at present. The destruction of the common
house-fly by "_papier Moure_," by decoctions of quassia, by various
traps, and by the so-called "catch 'em alive," is tried here and there,
now and then, by some grocer, confectioner, or housewife angry at the
spoliation and defilement caused by these little marauders. But there
is no concerted continuous action--which after all would be neither
difficult nor expensive--and consequently no marked success. Experiments
with a view of finding out new modes of fly-killing are few and far
between.
Every one must occasionally have seen, in autumn, flies as if cemented
to the window-pane, and surrounded with a whitish halo. That in some
seasons numbers of flies thus perish--that the phenomenon is due to a
kind of fungus, the spores of which readily transfer the disease from
one fly to another--we know. But here our knowledge is at fault. We
have not learnt why this fly-epidemic is more rife in some seasons than
others. We are ignorant concerning the methods of multiplying this
fungus at will, and of launching it against our enemies. We cannot tell
whether it is capable of destroying _Stomoxys calcitram_, the blowflies,
gadflies, gnats, mosquitoes, etc. Experiment on these points is rendered
difficult by the circumstance that the fungus is rarely procurable
except in autumn, when some of the species we most need to destroy are
not to be found. Another question is whether the fungus, if largely
multiplied and widely spread, might not prove fatal to other than
Dipterous insects, especially to the Hymenoptera, so many of which,
in their character of plant-fertilizers, are highly useful, or rather
essential to man.
Another fungus, the so-called "green muscardine" (_Isaria destructor_),
has been found so deadly to insects that Prof. Metschnikoff, who is
experimenting upon it, hopes to extirpate the _Phylloxera_, the Colorado
beetle, etc., by its agency.
Coming to better known and still undervalued fly-destroyers, we have
interfered most unwisely with the balance of nature. The substitution of
wire and railings for live fences in so many fields has greatly lessened
the cover both for insectivorous birds and for spiders. The war waged
against the latter in our houses is plainly carried too far. Whatever
may be the case at the Cape, in Australia, or even in Southern Europe,
no British species is venomous enough to cause danger to human beings.
Though cobwebs are not ornamental, save to the eye of the naturalist,
there are parts of our houses where they might be judiciously tolerated:
their scarcity in large towns, even where their prey abounds, is
somewhat remarkable.
But perhaps the most effectual phase of man's war against the flies will
be negative rather than positive, turning not so much on putting to
death the mature individuals as in destroying the matter in which the
larvae are nourished. Or if, from other considerations, we cannot
destroy all organic refuse, we may and should render it unfit for the
multiplication of these vermin. We have, indeed, in most of our large
towns and in their suburbs, abolished cesspools, which are admirable
breeding-places for many kinds of Diptera, and which sometimes presented
one wriggling mass of larvae. We have drained many marshes, ditches,
and unclean pools, rich in decomposing vegetable matter, and have thus
notably checked the propagation of gnats and midges. I know an instance
of a country mansion, situate in one of the best wooded parts of the
home counties, which twenty years ago was almost uninhabitable, owing to
the swarms of gnats which penetrated into every room. But the present
proprietor, being the reverse of pachydermatous, has substituted covered
drains for stagnant ditches, filled up a number of slimy ponds as
neither useful nor ornamental, and now in most seasons the gnats no
longer occasion any annoyance.
But if we have to some extent done away with cesspools and ditches, and
have reaped very distinct benefit by so doing, there is still a grievous
amount of organic matter allowed to putrefy in the very heart of our
cities. The dust bins--a necessary accompaniment of the water-carriage
system of disposing of sewage--are theoretically supposed to be
receptacles mainly for organic refuse, such as coal-ashes, broken
crockery, and at worst the sweepings from the floors. In sober fact
they are largely mixed with the rinds, shells, etc., of fruits and
vegetables, the bones and heads of fish, egg-shells, the sweepings out
of dog-kennels and henhouses, forming thus, in short, a mixture of evil
odor, and well adapted for the breeding-place of not a few Diptera.
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