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NEWS

of reasoning of which I need not give you any account,
he has arrived at the conclusion that the diameter of the
molecule of a gas is about the millionth part of a milli-
metre, or the seven hundredth part of the length of a
wave of red light. A cubic millimetre will therefore con-
tain 866 billions of such molecules; or if the gas were
condensed to a liquid, a trillion. A trillionth of a milli-
gramme, he believes, will represent the atomic unit of
weight.

Commercial and Scientific Analyses.

To the Editor of the CHEMICAL NEWS.
SIR,-Allow me a few lines to reply to a grumbling critic.
Mr. Denham Smith, who, in the CHEMICAL NEWS of
November 24, makes a desperate attempt to "cut up"
my paper on the new phosphate rock of North Wales;
and in the next number (December 1) vents his spleen
upon Mr. Carter Bell, the author of an interesting paper
on Alum, lately published in your valuable journal.

taken the mineral for wavellite. I mentioned that Mr. Talling had long ago sent me a mineral which I thought likely (and which proved) to be the same, and that he had sent them as wavellite, but with a doubt on this point. I added, that on one of the bits Mr. Talling had sent me (which were in every respect inferior to the specimen shown to the Society) had found one little splinter-like crystal presenting the bright plane, with two others, that, though very poor, seemed real planes; that one of these (apparently a prism plane) gave a tolerable measurement of 90° with the brilliant plane, and the other a measurement with it of nearly 90°, but oscillating on each side of 90°. The specimens themselves were not at all like the Stennagwyn wavellite, and these measurements made the resemblance still more problematical. Furthermore, with my absolute want of every sufficient means of making a qualitative analysis or even a blowpipe experiment in the British Museum, I was able only to establish the fact of the mineral being a phosphate.

On these grounds I could only endorse Mr. Talling's There being no grounds whatever at present for calling the mineral oblique, much less to assign a symbol to any plane on it, I said it was quite as likely to belong to one of the rectangular systems. I am, &c., NEVIL STORY MASKELYNE.

British Museum, November 30, 1865.

As far as my own case goes, the very fact criticised-query.
namely, the deduction of chemical formulæ from commer-
cial analyses made in my laboratory-simply proves that
these analyses are done with more than ordinary care;
and if Mr. Denham Smith is of opinion that analyses on
which large pecuniary interests are at stake should not
be made with as much accuracy as possible, I beg to differ
from him entirely, and to assure him that when a com-
mercial analysis is entrusted to me it receives just the
same attention, to ensure accuracy of results, as if it were
a research of a purely scientific nature. If, instead of
grun.bling at what others do, Mr. Denham Smith would
endeavour to produce something himself, it would be
"more becoming." When I compare my note upon the
new phosphate rock with his column of nonsense, I apply
to a critic of "his stamp" a slightly modified edition of
the old French saying, "Je ne suis pas si bête que vous
avez l'air!"
I am, &c.

T. L. PHIPSON, Ph.D., F.C.S., &c.

4, The Cedars, Putney, London, S. W.

The Vacant Chemical Professorship at Oxford.

To the Editor of the CHEMICAL NEWS.
SIR,-Could not the University of Oxford usefully imitate
the College of France, and change the Aldrichian Profes-
sorship into one of Organic Chemistry? Modern che-
mistry can be studied from two points of view; and in
these days, perhaps, the science could be best taught by the
exclusive consideration of the so-called organic compounds.
Mineral chemistry would be mainly occupied with its
technological applications; but with these the principles
of the science would of course receive full illustration.
I am, &c.,
CHEMICUS.

December 5.

New Cornish Minerals.

To the Editor of the CHEMICAL NEWS.
SIR,-My attention has been called to the report in your
journal of November 10 of the meeting for that week of
the Chemical Society, in which I find my language rather
erroneously reported. I must therefore ask you to correct
the doubtless unintended distortion of my words in so far
as it has any scientific bearing.

I did not say that the hydrated cerium phosphate occurs
in square prisms, which, of course, would imply its being
pyramidal.

The chemist who introduced the mineral, and who spoke before the Society with a diffidence on the crystallographic part of his subject that might have been well adapted in the paper recently printed in the Journal, stated that he had sent it to Professor Miller at Cambridge, who, however, could not meet with any angles good enough for measurement. He also stated that he had himself at first

MISCELLANEOUS.

The Copper Smoke Question.-It is well known that the utilisation of copper smoke has attracted great attention of late years, and only a few weeks ago particulars of a German invention in course of adoption at Messrs. Vivian and Sons' works, Swansea, were given in the Times. Mr. H. H. Vivian, M.P., announced at a public meeting since held that he had every confidence in the success of the invention, and that in a short time the copper smoke from his works, which had hitherto been so injurious to the land around, would not only be rendered innoxious, but of great commercial value, by condensing it through various processes to sulphuric acid. Within the last few weeks Mr. Thomas Bell has brought forward another invention, which, since his letters in the Times, has attracted considerable attention. That gentleman has visited Swansea, the seat of the copper smelting trade, and he was introduced to the copper smelters at the last ticketing meeting, when he laid his plans before the parties then present, and he was invited to visit several of the principal local establishments in order to test the invention. From these facts it is inferred that before long the injury caused by the copper smoke will not only be neutralised, but the smelters will reap a handsome return from its utilisation.-Times.

Use of Ammoniacal Liquor to Remove Sulphur from Gas.—In the last number of the Journal of Gas Lighting, &c., Professor Anderson gives the following summary of the results of some experiments made at the Taunton gas-works:-" 1. That in the experiments conducted at Taunton gas-works, when the sulphur was reduced by "scrubbing" (with ammoniacal liquor) from the proportion 198 grains to 12'92 per 100 feet, the illuminating power of the gas so treated underwent no deterioration of illuminating power. Further experiments, made with all the precautions which such operations on the large scale would admit of, contribute very much to show that the illuminating power of the gas is actually increased by the operation. 2. That the results obtained at Taunton gas-works are confirmed by other experiments, in which, whilst it was found that over 50 per cent. of the sulphur in the form of bisulphide of carbon was removed by the "scrubbing," the illuminating power of the gas was some

what increased." The above results, we may say, understate the results obtained at other gas-works-Nottingham, for example-where we believe it has been found that nine-tenths of the sulphur is removeable by scrubbing with ammoniacal liquor.

Gun-cotton. — The Vienna correspondent of the Times says:-"By order of the Emperor the use of guncotton by the Austrian artillery and corps of engineers is prohibited. If the cotton now on hand cannot soon be sold it is to be destroyed. A few years ago forty batteries of eight guns were made, all of which were to be charged with gun-cotton instead of powder, and now they must

be re-cast."

necessary for its own illumination and warmth within a few miles of its own surface? I trust I have advanced a sufficient number of facts, and deduced a sufficient number of arguments from them, to prove that philosophers are mistaken in supposing that light and heat come from the Treatment of the Cattle Plague with Alkaline sun in mechanical association with the "actinic" chemical Sulphites. We are glad to find that the treatment we rays, which I call chemical or ignipotent power. Surely, recommended when the presence of the cattle plague in if it be admitted that active chemical power (alone) comes England was first made public has been adopted with some from the sun, as I am contending for, there can be no success, at all events, as a prophylactic measure. A great difficulty in understanding that such power, while correspondent writes to the Daily Review that all the passing through the earth's atmosphere, excites the inanimals dosed with sulphites before an attack recovered, flammable matter contained therein into a state of comwhile all those not dosed died. We learn from wholesale bustion to supply the earth with the light and heat it chemists that the sulphites are just now in great demand, receives. If this be admitted, all further difficulty in and we hope they will have extensive trials. understanding the chemistry of nature is at an end. in the received theories, which I have endeavoured to Instead of the wasteful, destructive consequences involved expose, each heavenly body would supply the proper fuel, at the proper time, and in the proper quantity for its own illumination and warmth, they depending on their suns, and their suns depending upon them for an exchange of chemical power to excite and govern the combustion necessary for their respective requirements; in which case Mercury, instead of being in an incandescent state, and Venus in a boiling state, the surfaces of those planets may possess the same degrees of temperature as the earth possesses; and instead of Mars, the asteroids, Jupiter, Saturn, Herschel, and Neptune existing under the influence of insufferable cold, their supply of fuel may return them suitable temperatures for the existence of similar descriptions of animal and vegetable life with those existing on the earth; and the same with the sun itself. Permit me to invite you, on the first clear, bright day, to satisfy yourselves that combustion is actually going on in the earth's atmosphere continually. This may be done as follows:If you will stand with your backs to the sun, and look in a vacant manner for a minute or two towards the cerulean sky, you will discover an infinite number of infinitesimal but very distinct meteors, constantly igniting, travelling a short distance, and then expending themselves by combustion. They are so numerous and their movements are so eccentric as to resemble illuminated miniature flakes of snow during a violent snow-storm. These small meteors result from the combustion in the atmosphere of minute streams of compound hydrogen gas, which inflame as they are produced, and supply the light upon which the descending rays of light feed during their descent from their infantile source, till they impinge on, and are absorbed by, the earth's surface. For the information of the existence of these infinitesimal meteors I am indebted to the late Professor Maverly, who, for fifty years, was astronomer and natural philosopher at the observatory attached to the Royal Naval Academy at Gosport. He was one of the first to oppose my views, as contained in the paper I have been reading, but after six years of opposition he became a convert, and was the first to acknowledge himself as such in the public newspapers in the year 1857."

British Rainfall.-Mr. G. F. Symons writes to us:-"I have to ask your readers' attention for a few moments to a request on the above subject, the importance of which in relation to engineering, and drainage questions is well known. It is now some years since I began collecting returns of the fall of rain; but my main difficulty has been to find out the persons who keep such records, and one of the most obvious sources of assistance is the public press; I now, therefore, ask from each and every journal in the British isles their all-powerful aid. When the collection was first organised, in 1860, scarcely 200 persons were known to observe and record the rain fall; by steady perseverance and the aid of a portion of the press, the number has been raised until there are now more than 1200 places whence returns are regularly received. Still, I know there are many more, probably hundreds, who have either never heard of the establishment of a central depôt to which copies of all rain records should be sent, or they have been too diffident to send them. It is of paramount importance to gather these, and make the tables yet more complete. I therefore beg leave through your columns to ask every reader to think for a moment if he or she knows of any one who keeps, or has kept, a rain-gauge; or who has any tables of rain-fall (or old weather journals) in their possession. And if they do know of such persons, I ask them on behalf of science, of my fellow-observers, and on my own behalf, to use every effort to secure their assistance, and to favour me

with their names and addresses. We want old records, we want records for the present year, and from many parts of the country we want returns for the future, if a few persons will notify to me their willingness to assist, and to pay 108. 6d. for the very cheap and simple gauge now supplied." Mr. Symons' address is 136, Camden Road, N.W.

Popular Scientific Teaching.- Chemists must laugh as well as other men, and therefore we make no apology for introducing the following quotation from the second of two lectures, "On the Chemistry of Nature," delivered at Ryde, to the Isle of Wight Philosophical and Scientific Society, by G. F. Harrington, Esq., L.D.S. :"I have already explained that a large proportion of the earth's atmosphere consists of compound inflammable gas; indeed, some philosophers have gone so far as to say that if the nitrogen were to be withdrawn from the atmosphere the remaining portion would combine with the earth's surface in a general state of violent conflagration. This being the case, is it reasonable to suppose that the earth is depending for light and heat upon the sun, which is 95,000,000 miles away, when it has all the materials

ANSWERS TO CORRESPONDENTS.

All Editorial Communications are to be addressed to the EDITOR, and Advertisements and Business Communications to the PUBLISHER, at the Office, 1, Wine Office Court, Fleet Street, London, EC. Private letters for the Editor must be so marked.

*In publishing letters from our Correspondents we do not thereby adopt the views of the writers. Our intention to give both sides of a do not agree. question will frequently oblige us to publish opinions with which we

F. J. Fraser-See various papers in vol. x. of CHEMICAL NEWS. K. K.-A method of produc ng tetrachloride of carbon cheaply would, no doubt, be of great commercial value.

Alpha-Mr. Gossage can give you the information. We know of no statistics later than those which will be found in the Report of the Committee of the House of Lords on the Alkali Works Bill. The Board of Trade Returns will give you the exports of soda regularly. Received.-Trenham Reeks; E. Osborne; H. R,

NEWS

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I. Hydrocarbons from Coal-tar Naphtha.-In presenting the results of a re-examination of a series of substances upon which so much labour has been already bestowed, it may confer an interest on the subject to state briefly some of the more important results and conclusions arrived at by previous investigators.

Mansfield's view of the composition of this naphtha. In regard to the results he obtained, he says they fully confirm those of Mansfield. Of the body which Mansfield thought identical with cymole, and of the oil more volatile than benzole, Ritthausen obtained quantities too small for investigation. In regard to the latter, however, he remarks that to Mansfield's account he can add " that its nitro-product quite resembles that of benzole, and hence that at all events it belongs to the series CnHn-6, and perhaps has the formula C1H." Ritthausen omitted to analyse and determine the vapour density of any one of the substances; he therefore adds nothing gives the boiling-point of benzole at 80°, of toluole at 109°, and of the so-called cumole at 130°-140°, which will be found to agree very nearly with my own determinations.

more than a confirmation of the results of Mansfield. He

Church, in the following year, published a paper on the "Determination of Boiling-points in the Benzole Series." I cannot better present his results than by quoting the following table :

The discovery by Faraday in 1825 of benzole (" bicarburetted hydrogen ") in the oil compressed from coal-gas rendered it highly probable, and, indeed, led this distinguished philosopher to suspect, that this substance might be found in coal-tar naphtha. His search for it, however, proved unsuccessful, it having been first detected by Hofmann in 1845. This chemist, however, did not attempt to isolate the body, and the bare fact of its presence appears to be all that was definitely known of the composition of coal-tar naphtha prior to 1849, in which year Mansfield published his elaborate and valuable research, being the first effort at a proximate analysis of this mixture which appears to have been attended with any considerable measure of success. may be said that little has since been added to our knowledge of this subject. Notwithstanding the in-coal completeness of his separations of the hydrocarbons, the extent to which he carried them, with the limited means employed, is truly remarkable, and could not have been accomplished without an expenditure of labour and a degree of patient endurance which only those who have experienced the tediousness of such operations can appreciate.

It

Mansfield claimed to show that the light coal-tar naphtha is composed of a mixture of four distinct hydrocarbons, boiling within the range 80° to 175° C., and probably having the general formula CnHn - 6. The first of these, which he found to boil constant at 80°, was proved to be identical with benzole CH6. The second, boiling about 113°, was determined, from certain reactions, to be identical with toluole, CH The special study of this body was deferred, however, with the remark that it had not yet been isolated in a state of sufficient purity to claim an analysis. The third body, boiling about 140° to 1450, was said to present all the characteristics of cumole, C8H12; but this view was merely an expression of opinion in advance of anticipated results. Of the fourth body, boiling at about 170° to 175°, Mansfield remarks that it bears so strong a resemblance in odour and properties to cymole, CH as to induce the belief that this substance is identical with the hydrocarbon existing in oil of cumin. It thus appears that of the four bodies benzole was the only one which Mansfield had studied in any detail; yet his conjectures as to the identity of the other bodies, thrown out by way of preliminary notices of results acknowledged to be incomplete, have been extensively quoted and generally received as established facts. In addition to the bodies already mentioned, Mansfield also discovered a body more volatile than benzole, having an alliaceous odour, and which he found to boil betwen 60° and 70°.

Ritthausen made a re-examination of the light coal tar naphtha, in order to obtain the hydrocarbons in a state of greater purity, and to prove the correctness of

*Abridged from the Memoirs of the American Academy. VOL. XII. No. 315.-DECEMBER 15, 1865.

Formula.

Benzole, C12H Toluole, CH 147

10

=

Boiling-point, Difference, Ce 3 (C2H2) 80°8

6

22°5 22° 2

Xylole, CH C 5(CH2)126° Cumole, CH12 Ce 6(CH2(148° Cymole, CHC 7(CH) 170°22'3 7(C2H2)170°*7 Church states that he obtained all of these bodies from

naphtha, and also that he obtained benzole from benzoic acid, toluole from toluylic acid, xylole from wood spirit, cumole from cuminic acid, and cymole from oil of cumin; and that he has found the corresponding bodies from these different sources to be identical. It will be observed that Church claims to have discovered in coal tar a body boiling at 126°2, which he calls xylole, benzole series; whereas Mansfield and Ritthausen found thus supplying from this source a fifth member of the only four bodies within the range of temperature indicated by the table. It will also be observed that his determination of the boiling-point of toluole is much lower, and that of cumole much higher, than the corresponding determination of Mansfield and Ritthausen; thus giving room for a middle member between them, and preserving a remarkable uniformity of differenceviz., 22° and a fraction-between the boiling points of any two contiguous members, for the addition C2H2.

That the earlier investigators had found in coal-tar naphtha only the two lower members (C12H and CH) and the two upper members (CH, and CH14) was always to me an anomaly which I could not reconcile with any plausible theory in regard to the formation of these bodies; and I was led, therefore, to question whether the middle member (C16H10) had not been overlooked in making the separations. The alleged discovery of this body in coal naphtha by Church, together with the uniformity of boiling-point difference which he presented, and the apparent care with which the research had been conducted, led me to regard his results as more reliable than any previously published. I remained under this conviction until I had discovered the boiling-point dif ference of 30° in other series of hydrocarbons, which led me to doubt the accuracy of Church's determinations, and to consider those of Mansfield and Ritthausen as probably more correct.

In the first paragraph of his memoir Church remarks that," although doubts still remain as to the relations of these bodies to one another, yet their composition has been ascertained with certainty." It does not appear, however, that an analysis or vapour density of any one

member of the series as obtained from coal-tar, except berzole, has ever been published. As indicated by the title of his paper, it appears to have been the design of Church to treat only of the boiling points of these bodies; yet finding that his preparations of toluole— prepared both from coal naphtha and toluylic acid-gave a boiling point differing considerably from observations previously published, he took occasion to make analyses of this substance, which he regards as "perfectly satisfactory;" but he omits to give the details and numerical results. As he undertook to correct the work of his predecessors, to do which fairly would seem to require the publication of these details and numerical results, their omission is to be regretted. I am prompted to these remarks from having been led to undertake the tedious task of making a re-examination of coal-tar naphtha, mainly on account of the disagreement between Church's determinations, which I have found to be mostly incorrect, and those which had been previously published.

a

In addition to the bodies mentioned in the foregoing table Church alludes to the discovery of two other bodies, boiling respectively at 97° and 112°. Subsequently, in "Note on Parabenzole, a New Hydrocarbon from Coal Naphtha," he publishes the details of an investigation of the former of these two bodies, which he found to boil "perfectly constant at 97°5," and to be isomeric with benzole.

I think I shall be able to show in what follows:

1. That coal-tar naphtha contains only four hydrocarbons within the range of 80° to 170°, as taught by Mansfield and confirmed by Ritthausen.

2. That the benzole series within that range of temperature is limited to four members, and, therefore, does not contain five, as generally supposed.

3. That these four members have the boiling-points 80°, 110°, 140°, and 170° respectively; and, consequently, that the boiling-point difference in this series for an elementary difference of C2H2 is 30° instead of

22° and a fraction.

4. That the body obtained from coal-tar naphtha is not identical with cumole from cuminic acid, as assumed by Mansfield, nor even isomeric with it; but that it has the formula which has been assigned to xylole, containing C2H, less than that of cumole.

5. That the body obtained from coal-tar naphtha boiling at 170° is quite a different body from cymole from oil of cumin, these bodies differing from each other by C2H2.

6. That cumole from cuminic acid, and cymole from oil of cumin, do not even belong to the benzole series.

7. That the parabenzole of Church was in all probability only a mixture of benzole and toluole.

(To be continued.)

Formation of Nitrous Acid from Ammonia.-It is well known that ammonia is decomposed by permanganate of potash, and nitrogen evolved. It does not, however, appear to have been hitherto observed that a good deal of nitrous acid is formed at the same time. If the decolourised solution is filtered from the precipitated hydrated peroxide of manganese, and slowly evaporated to dryness, a mixture of carbonate and nitrite of potash is obtained. Abundant red fumes of nitrous acid will be evolved from the residue on the addition of an acid. W. -Annal. der Chem, und Pharm., November, p. 256.

NEWS

PHYSICAL SCIENCE.

Apparatus for the Detection of Explosive Gases in Mines.

THE lamentable accidents which from time to time occur in coal mines, causing such great destruction of life and property, have engrossed the attention of scientific men ever since the results of the study of natural phenomena have been practically applied to every-day life. Numerous methods of illuminating the mines in such a manner as to prevent the ignition of the combustible gases, but at the same time producing sufficient light to enable the men to work in comfort, have been suggested and employed with varying success.

Next to preventing the accumulation and explosion of inflammable gas in the mines, the possibility of ascertaining with safety its presence is a matter of some importance, as it would enable the overseer to guard against incautious working in a dangerous part of the pit, and to prevent too great an accumulation of the explosive mixture by directing special attention to the ventilation. The process formerly employed by the miners to detect the presence of the inflammable gas, and which cannot be recommended as a safe one, was to bring a lighted candle into the suspected atmosphere, when the peculiar shape assumed by the candle flame gave the required information. This process cannot be too strongly reprehended, and it is probably the cause of many of the fearful accidents which have already taken place.

Another method, which is much more safe, but which

is not unattended with danger, is to observe the flame of a Davy lamp. A careful viewer invariably reduces the flame of the Davy lamp to the smallest size that will emit white light before testing for gas, or, as he calls it, "trying a fiery place." When the atmosphere consists of a violently explosive mixture, one hears a peculiar and sharp click, and observes a rapid combustion of the gas within the wire gauze of the safety lamp; when the quantity of carburetted hydrogen is less, the flame of the lamp elongates; and when the quantity is very small, a peculiar lambent cap of a bluish colour is observed covering the flame of the lamp. These indications can only be learnt by experience in the mines, and when not properly attended to might give rise to disastrous results. Should the atmosphere be explosive, the viewer or fireman lowers his lamp very slowly and cautiously until it has passed out of the explosive mixture, which usually occupies the upper part of the gallery of a mine, and travels in that position, notwithstanding the law of diffusion. There are many wellthe Davy lamp in a quiet atmosphere, and where the authenticated cases of explosions through the gauze of lamps after the explosions have been ascertained to be in good order.

A very ingenious instrument has recently been devised for the detection and quantitative estimation of the explosive gases by Mr. G. F. Ansell, of the Royal Mint. The instrument, which may be constructed in several different forms, is based upon the well-known law in accordance with which gases gradually mix with one another through porous septa, and even through some materials which do not appear to possess any interstices through which the gases might pass.

If a tube blown out into a cup at one end (Fig. 1), and bent in the form of the letter U be filled with mercury, so that the mercury stands in the cup, and the cup closed by a piece of porous tile cemented on by a resinous varnish, a

very serviceable indicator is obtained. On bringing this used instead of the glass vessel (b) in figure 2, but it instrument into an atmosphere containing a gas differ- does not give better results than those attained by the ing from that contained within the cup, perceptible dif. | tile (a).

fusion takes place through the unglazed earthenware.

FIG. 1.

-75

-30

If the cup be filled with air and the apparatus introduced into an atmosphere of hydrogen, the hydrogen will pass into the cup more rapidly than the air will pass out, according to the well-known law that "gases diffuse into one another in the inverse proportion of the square roots of their specific gravities." The specific gravity of hydrogen being 1, that of air is 14'4. As the square root of 144 is 38, for every part of air which diffuses out of the cup 3.8 parts of hydrogen will pass in through the porous tile. Thus the pressure on the mercury within the closed limb will exceed that on the liquid in the open limb, and a corresponding elevation of the mercury in the open limb will result. When the maximum effect has been produced, the pressure within the cup will gradually force the gas through the porous diaphragm until the mercury stands level in both limbs. At this point the gases within and without the apparatus possess the same composition, but any change of proportions in the external atmosphere is immediately indicated by the level of the mercury. If the instrument be removed into the air the hydrogen within will immediately diffuse outward, and a rise of the mercury in the closed limb will result.

If the apparatus containing air be placed in an atmo sphere of a gas of greater density than the air-as, for instance, carbonic acid, diffusion will take place, but the The specific converse phenomena will be observed.

FIG. 3.

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gravities of air and carbonic acid being in the proportions of 14'4 to 22, the diffusion will take place in the ratio of 47 to 38-i.e., for every 47 volumes of air which pass outwards, 3.8 of carbonic acid will pass inwards, so that the pressure on the mercury in the open limb will exceed that in the closed limb, and the mercury in the latter will rise; the alteration of level obviously being less than in the previous case, in which hydrogen was without the diaphragm. Of course, the theoretical elevation and depression of the mercury can in no case be observed, for during the whole time that diffusion is going on effusion takes place in consequence of the increased or diminished pressure of the apparatus. Mr. Ansell has constructed several pieces of apparatus on this principle. One (Fig. 1) consists simply of the U-tube with a scale graduated so as to indicate the percentage of mine gas present. In another form of the apparatus (Fig. 2) a is a piece of biscuitware cemented to a glass vessel (6), which at its lower end communicates with a U-tube containing mercury, on which, as it rises in the open limb, there floats a Another apparatus (Fig. 4) on the same principle has small weight, to which is fastened a cord passing over a been constructed by enclosing a U-tube with a bulb conpulley, and counterbalanced on the opposite side, the taining mercury in an inverted porous battery cell. The rise and fall of the mercury causing the pulley to re-edge of the cell is firmly cemented on to a piece of volve and to indicate the alteration of pressure by the wood; a small metal weight floats on the surface of the movement of a pointer on a dial (c). This is for use only mercury in the tube, and is attached to a piece of string, on occasion of a sudden irruption of fire-damp. which passes over a pulley, and, by the alteration of the level of the mercury in the tube, moves an index,

Figure 3 is a section of a porous battery cell which is

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