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Correspondence-Miscellaneous.

277 Dec. 8, 1865. of reasoning of which I need not give you any account, taken the mineral for wavellite. I mentioned that Mr. he has arrived at the conclusion that the diameter of the Talling had long ago sent me a mineral which I thought molecule of a gas is about the millionth part of a milli- likely (and which proved) to be the same, and that he had metre, or the seven hundredth part of the length of a sent them as wavellite, but with a doubt on this point. I wave of red light. A cubic millimetre will therefore con- added, that on one of the bits Mr. Talling had sent me tain 866 billions of such molecules; or if the gas were (which were in every respect inferior to the specimen condensed to a liquid, a trillion. A trillionth of a milli- shown to the Society) I had found one little splinter-like gramme, he believes, will represent the atomic unit of crystal presenting the bright plane, with two others, that, weight.

though very poor, seemed real planes ; that one of these

(apparently a prism plane) gave a tolerable measurement Commercial and Scientific Analyses.

of goo with the brilliant plane, and the other a measure. To the Editor of the CHEMICAL News.

ment with it of nearly 90°, but oscillating on each side of

90°. The specimens themselves were not at all like the SIR,—Allow me a few lines to reply to a grumbling critic. Stennagwyn wavellite, and these measurements made the Mr. Denham Smith, who, in the CHEMICAL News of resemblance still more problematical. Furthermore, with November 24, makes a desperate attempt to "cut up” my absolute want of every sufficient means of making a my paper on the new phosphate rock of North Wales ; qualitative analysis or even a blowpipe experiment in the and in the next number (December 1) rents his spleen British Museum, I was able only to establish the fact of upon Mr. Carter Bell, the author of an interesting paper the mineral being a phosphate. on Alum, lately published in your valuable journal.

On these grounds I could only endorse Mr. Talling's As far as my own case goes, the very fact criticised

query. There being no grounds whatever at present for namely, the deduction of chemical formulæ from commercial analyses made in my laboratory-simply proves that calling the mineral oblique, much less to assign a symbol

to any plane on it, I said it was quite as likely to belong these analyses are done with more than ordinary care ;

to one of the rectangular systems. and if Mr. Denham Smith is of opinion that analyses on

I am, &c., which large pecuniary interests are at stake should not

NEVIL STORY MASKELYNE. be made with as much accuracy as possible, I beg to differ

British Museum, November 30, 1865. from him entirely, and to assure him that when a commercial analysis is entrusted to me it receives just the same attention, to ensure accuracy of results, as if it were

MISCELLANEOUS. a research of a purely scientific nature. If, instead of grunıbling at what others do, Mr. Denham Smith would endeavour to produce something himself, it would be The Copper Smoke Question.—It is well known “more becoming.", When I compare my note upon the that the utilisation of copper smoke has attracted great new phosphate rock with his column of nonsense, I apply attention of late years, and only a few weeks ago parto a critic of "his stamp" a slightly modified edition of ticulars of a German invention in course of adoption at the old French saying, “ Je ne suis pas si béle que vous Messrs. Vivian and Sons' works, Swansea, were given in avez l'air !I am, &c.

the Times. Mr. H. H. Vivian, M.P., announced at a T. L. Phipson, Ph.D., F.C.S., &c. public meeting since held that he had every confidence in 4, The Cedars, Putney, London, S.W.

the success of the invention, and that in a short time the

copper smoke from his works, which had hitherto been The Vacant Chemical Professorship at Oxford.

so injurious to the land around, would not only be renTo the Editor of the CHEMICAL NEWS.

dered innoxious, but of great commercial value, by con

densing it through various processes to sulphuric acid. SIR,–Could not the University of Oxford usefully imitate Within the last few weeks Mr. Thomas Bell has brought the College of France, and change the Aldrichian Profes- forward another invention, which, since his letters in the sorship into one of Organic Chemistry!. Modern che | Times, has attracted considerable attention. That gentlemistry can be studied from two potants of view; and in

man has visited Swansea, the seat of the copper smelting these days, perhaps, the science could be best taught by the trade, and he was introduced to the copper smelters at the exclusive consideration of the so-called organic compounds. last ticketing meeting, when he laid his plans before the Mineral chemistry. would be mainly occupied with its parties then present, and he was invited to visit several of technological applications ; but with these the principles the principal local establishments in order to test the of the science would of course receive full illustration.

invention. From these facts it is inferred that before long I am, &c.,

CHEMICUS.

the injury caused by the copper smoke will not only be December 5.

neutralised, but the smelters will reap a handsome return

from its utilisation.-Times. New Cornish Minerals.

Use of Ammoniacal Liquor to Remove Sulphur To the Editor nf the Chemical News.

from Gas.—In the last number of the Journal of Gas SIR,—My attention has been called to the report in your Lighting, &c., Professor Anderson gives the following journal of November 10 of the meeting for that week of summary of the results of some experiments made at the the Chemical Society, in which I find my language rather | Taunton gas-works :-"1. That in the experiments conerroneously reported. I must therefore ask you to correct ducted at Taunton gas-works, when the sulphur was rethe doubtless unintended distortion of my words in so far duced by "scrubbing" (with ammoniacal liquor) from the as it has any scientific bearing.

proportion 19.8 grains to 12'92 per 100 feet, the illumiI did not say that the hydrated cerium phosphate occurs nating power of ihe gas so treated underwent no deteriorain square prisms, which, of course, would imply its being tion of illuminating power. Further experiments, made pyramidal.

with all the precautions which such operations on the The chemist who introduced the mineral, and who spoke large scale would admit of, contribute very much to show before the Society with a diffidence on the crystallographic that the illuminating power of the gas is actually increased part of his subject that might have been well adapted in by the operation. 2. That the results obtained at Taunton ihe paper recently printed in the Journal, stated that he gas-works are confirmed by other experiments, in which, had sent it to Professor Miller at Cambridge, who, how- whilst it was found that over 50 per cent. of the sulphur ever, could not meet with any angles good enough for in the form of bisulphide of carbon was removed by the measurement. He also stated that he had himself at first, "scrubbing," the illuminating power of the gas was some278

MiscellaneousAnswers to Correspondents.

CHEMICAL NEWE,

Dec. 8, 1865.

what increased." The above results, we may say, under- necessary for its own illumination and warmth within a state the results obtained at other gas-works-Notting- few miles of its own surface? I trust I have advanced a ham, for example--where we believe it has been found sufficient number of facts, and deduced a sufficient number that nine-tenths of the sulphur is removeable by scrubbing of arguments from them, to prove that philosophers are with ammoniacal liquor.

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 in. animals 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. Gun-cotton. — The Vienna correspondent of the in the received theories, which I have endeavoured to

Instead of the wasteful, destructive consequences involved Times says :-"By order of the Emperor the use of gun expose, each heavenly body would supply the proper fuel, cotton by the Austrian artillery and corps of engineers at the proper time, and in the proper quantity for its own is prohibited. If the cotton now on hand cannot soon be illumination and warmth, they depending on their suns, sold it is to be destroyed. A few years ago forty batteries and their suns depending upon them for an exchange of of eight guns were made, all of which were to be charged chemical power to excite and govern the combustion with guu-cotton instead of powder, and now they must necessary for their respective requirements; in which be re-cast."

case Mercury, instead of being in an incandescent state, British Rainfall.-Mr. G. F. Symons writes to and Venus in a boiling state, the surfaces of those planets us :-"I have to ask your readers’ atiention for a few may possess the same degrees of temperature as the earth moments to a request on the above subject, the import- possesses; and instead of Mars, the asteroids, Jupiter, ance of which in relation to engineering, and drainage Saturn, Herschel, and Neptune existing under the influence questions is well known. It is now some years since I of insufferable cold, their supply of fuel may return them began collecting returns of the fall of rain; but my main suitable temperatures for the existence of similar descripdifficulty has been to find out the persons who keep such tions of animal and vegetable life with those existing on records, and one of the most obvious sources of assistance the earth; and the same with the sun itself. Permit me is the public press; I now, therefore, ask from each and to invite you, on the first clear, bright day, to satisfy every journal in the British isles their all-powerful aid. yourselves that combustion is actually going on in the earth's When the collection was first organised, in 1860, scarcely atmosphere continually. This may be done as follows :200 persons were known to observe and record the rain. If you will stand with your backs to the sun, and look in fall; by steady persererance and the aid of a portion of a vacant manner for a minute or two towards the cerulean the press, the number has been raised until there are now sky, you will discover an infinite number of infinitesimal more than 1200 places whence returns are regularly but very distinct meteors, constantly igniting, travelling a received. Still, I know there are many more, probably short distance, and then expending themselves by comhundreds, who have either never heard of the establish- bustion. They are so numerous and their movements are ment of a central depôt to which copies of all rain records so eccentric as to resemble illuminated miniature flakes of should be sent, or they have been too diffident to send snow during a violent snow-storm. These small meteors them. It is of paramount importance to gather these, and result from the combustion in the atmosphere of minute make the tables yet more complete. I therefore beg leave streams of compound hydrogen gas, which inflame as they through your columns to ask every reader to think for a

are produced, and supply the light upon which the moment if he or she knows of any one who keeps, or has descending rays of light feed during their descent from kept, a rain-gauge; or who has any tables of rain-fall (or their infantile source, till they impinge on, and are absorbed old weather journals) in their possession. And if they by, the earth's surface. For the information of the existdo know of such persons, I ask them on behalf of science, ence of these infinitesimal meteors I am indebted to the of my fellow-observers, and on my own behalf, to uselite Professor Javerly, who, for fifty years, was astronomer every effort to secure their assistance, and to favour me and natural philosopher at the observatory attached to the with their names and addresses. We want old records, Royal Naval Academy at Gosport. He was one of the we want records for the present year, and from many first to oppose my views, as contained in the paper I have parts of the country we want returns for the future, if a

been reading, but after six years of opposition he became few persons will notify to me their willingness to assist,

a convert, and was the first to acknowledge himself as and to pay 108. 6d. for the very cheap and simple gauge such in the public newspapers in the year 1857" now supplied." Mr. Symons' address is 136, Camden Road, N.W. Popular Scientific Teaching. - Chemists must

ANSWERS TO CORRESPONDENTS. laugh as well as other men, and therefore we make no All Editorial Communications are to be addressed to the Editor, apology for introducing the following quotation from the

and Advertisements and Business Communications to the PUBLISHER, at second of two lectures, “ On the Chemistry of Nature,"

the Office, 1, Wine Office C. urt, Fleet Street, London, E.C. Private

letters for the Editor must be so marked. delivered at Ryde, to the Isle of Wight Philosophical and Scientific Society, by G. F. Harrington, Esq., L.D.S.:- In jinblishing letters from our Correspondents we do not thereby :: I have already explained that a large proportion of the adopt the views of the writers. Our intention to give both sides of a

question will frequently oblige us to publish opinions with which we 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

F. J. Frasei.-See various papers in vol. x. of CHEMICAL NEWS. the rema ning portion would combine with the earth's would, no doubt, be of great com tercial value.

K. K.-A method of produc ng tetrachloride of carbon cheaply surface in a general state of violent conflagration. This Alpha. - Mr. Gossage can give you the information. We know of being the case, is it reasonable to suppose that the earth no siatistics later than those wbich will be found in the Report of the is depending for light and heat upon the sun, which is Comunittee of the House of Lords on the Alkali Works Bill. The

Board of Trade Returns will give you the exports of soda regularly, 95,000,000 miles away, when it has all the materials

Received. --Trenham Roeks; E. Osborne; H. R,

do not agree.

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, } Researches on the Volatile Hydrocarbons. Dec. 15, 1865.

279 SCIENTIFIC

Mansfield's view of the composition of this naphtha. In AND ANALYTICAL

regard to the results he obtained, he says they fully CHEMISTRY.

confirm those of Mansfield. Of the body which Mans. field thought identical with cymole, and of the oil more

volatile than benzole, Ritthausen obtained quantities too Researches on the Volatile Hydrocarbons, by C. M. WARREN.

small for investigation. In regard to the latter, however,

he remarks that to Mansfield's account he can add " that 1. Hydrocarbons from Coal-tar Naphtha:-In its nitro-product quite resembles that of benzole, and presenting the results of a re-examination of a series of hence that at all events it belongs to the series CnHn-6, substances upon which so much labour has been already and perhaps has the formula C1.H." Ritthausen bestowed, it may confer an interest on the subject to omitted to analyse and determine the vapour density of state briefly some of the more important results and any one of the substances; he therefore adds nothing conclusions arrived at by previous investigators. more than a confirmation of the results of Mansfield. He

The discovery by Faraday in 1825 of benzole (" bicar- gives the boiling point of benzole at 80°, of toluole at buretted hydrogen ”) in the oil compressed from coal-gas 109°, and of the so-called cumole at 1300-140°, which rendered it highly probable, and, indeed, led this dis- will be found to agree very nearly with my own detertinguished philosopher to suspect, that this substance minations. might be found in coal-tar naphtha. His search for it, Church, in the following year, published a paper on however, proved unsuccessful, it having been first de- the “ Determination of Boiling-points in the Benzole tected by Hofmann in 1845. This chemist, however, did Series.” I cannot better present his results than by not attempt to isolate the body, and the bare fact of its quoting the following table :presence appears to be all that was definitely known of

Formula. Boiling-point. Difference, the composition of coal-tar naphtha prior to 1849, in Benzole, C12H which fear Mansfield published his elaborate and Toluole, CA C 4C, H, 10397 valuable research, being the first effort at a proximate Xylole, CH, Co 5(CH,126°2

22°.5

22° 2 analysis of this mixture which appears to have been Cumole, CisHj2 = Co 6C,6,(148°4 attended with any considerable measure of success. It Cymole, CH - CricH,)170°

22°3 may be said that little has since been added to our

Church states that he obtained all of these bodies from knowledge of this subject. Notwithstanding, the in- coal naphtha, and also that he obtained benzole from completeness of bis separations of the hydrocarbons, the benzoic acid, toluole from toluylic acid, xylole from extent to which he carried them, with the limited means wood spirit, cumole from cuminic acid, and cymole from employed, is truly remarkable, and could not have been oil of cumin; and that he has found the corresponding accomplished without an expenditure of labour and a bodies from these different sources to be identical. It degree of patient endurance which only those who hare will be observed that Church claims to have discovered experienced the tediousness of such operations can in coal tar a body boiling at 126°2, which he calls zylole, appreciate. Mansfield claimed to show that the light coal-tar benzole series; whereas Mansfield and Ritthausen found

thus supplying from this source a fifth member of the naphtha is composed of a mixture of four distinct only four bodies within the range of temperature indiby drocarbons, boiling within the range 80° to 175° C., cated by the table. It will also be observed that his and probably having the general formula CnHn - 6. determination of the boiling-point of toluole is much The first of these, which he found 10 boil constant at 80°; lower, and that of cumole much higher, than the correwas proved to be identical with benzole CH The sponding determination of Mansfield and Ritthausen; second, boiling about !3°. was determined, from thus giving room for a middle member between them, certain reactions, to be identical with toluole, CiH, and preserving a remarkable uniformity, of difference, The special study of this body was deferred, however, viz., 22° and a fraction-between the boiling

points of with the remark that it had not yet been isolated in a ang two contiguous members, for the addition CH2 state of sufficient purity to claim an analysis. The

That the earlier investigators had found in coal-tar third body, boiling about 140° to 45°, was said to naphtha only the two lower members (C12H,

and C.Hs) present all the characteristics of cumole, C18H12; but this and the two upper members. (C19H12 and C20H14) was view was merely an expression of opinion in advance always to me an anomaly which I could not reconcile of anticipated results. of the fourth body, boiling at with any plausible theory in regard to the formation of about 170° to 175°, Mansfield remarks that it bears so these bodies; and I was led, therefore, to question strong a resemblance in odour and properties to cymole, whether the middle member (C16H70) had not been overC,H, as to induce the belief that this substance is looked in making the separations. The alleged discovery identical with the hydrocarbon existing in oil of cumin. of this body in coal naphtha by Church, together with the It thus appears that of the four bodies benzole was the uniformity of boiling-point difference which he presented, only one which Mansfield bad studied in any detail; yet and the apparent care with which the research had been his conjectures as to the identity of the other bodies, conducted, led me to regard his results as more reliable thrown out by way of preliminary notices of results than any previously published. I remained under this acknowledged to be incomplete, have been extensively conviction until I had discovered the boiling-point difquoted and generally received as established facts. In ference of 30° in other series of hydrocarbons, which led addition to the bodies already mentioned, Mansfield also me to doubt the accuracy of Church's determinations, discovered a body more volatile than benzole, having an and to consider those of Mansfield and Ritthausen as alliaceous odour, and which he found to boil betwen 60°

probably more correct. and 70°.

In the first paragraph of his memoir Church remarks Ritthausen made a re-examination of the light coal that, " although doubts still remain as to the relations tar naphtha, in order to obtain the hydrocarbons in a of these bodies to one another, yet their composition has state of greater purity, and to prove the correctness of been ascertained with certainty.” It does not appear,

* Abridged from the Memoirs of the American Academy, however, that an analysis or vapour density of any one VOL. XII. No. 315.-DECEMBER 15, 1865.

280

Apparatus for the Detection of Explosive Gases in Mines.

CHEMICAL NEW,

Dec. 15, 1865.

member of the series as obtained from coal-tar, except

PHYSICAL SCIENCE. ber zole, hus 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

Apparatus for the Detection of Explosive Gases bodies ; yet finding that his preparations of toluole

in Mines. prepared both from coal naphtha and toluylic acid-gave The lamentable accidents which from time to time occur a boiling point differing considerably from observations in coal mines, causing such great destruction of life and previously published, he took occasion to make analyses property, have engrossed the attention of scientific men of this substance, which he regards as "perfectly satis- ever since the results of the study of natural phenofactory;" but he omits to give the details and nume- mena have been practically applied to every-day life. rical results. As he undertook to correct the work of Numerous methods of illuminating the mines in such a his predecessors, to do which fairly would seem to require manner as to prevent the ignition of the combustible the publication of these details and numerical results, gases, but at the same time producing sufficient light to their omission is to be regretted. I am prompted to enable the men to work in comfort, have been suggested these remarks from having been led to undertake the and employed with varying success. tedious task of making a re-examination of coal-tar Next to preventing the accumulation and explosion naphtha, mainly on account of the disagreement between of inflammable gas in the mines, the possibility of Church's determinations, which I have found to be mostly ascertaining with safety its presence is a matter of incorrect, and those which had been previously pub- some importance, as it would enable the overseer to guard lished.

against incautious working in a dangerous part of the In addition to the bodies mentioned in the foregoing pit, and to prevent too great an accumulation of the extable Church alludes to the discovery of two other bodies, plosive mixture by directing special attention to the boiling respectively at 979 and 112°. Subsequently, in ventilation. The process formerly employed by the a “ Note on Parabenzole, a New Hydrocarbon from Coal miners to detect the presence of the inflammable gas, Naphtha," he publishes the details of an investigation of and which cannot be recommended as a safe one, was to the former of these two bodies, which he found to boil bring a lighted candle into the suspected atmosphere, "perfectly constant at 97°5," and to be isomeric with when the peculiar shape assumed by the candle flame benzole.

gave the required information. This process cannot be I think I shall be able to show in what follows:- too strongly reprehended, and it is probably the cause of

1. That coal-tar naphtha contains only four hydro-many of the fearful accidents which have already taken carbons within the range of 80° to 170°, as taught by

place. Mansfield and confirmed by Ritthausen.

Another method, which is much more safe, but which 2. That the benzole series within that range of tem of a Davy lamp. A careful viewer invariably reduces

is not unattended with danger, is to observe the flame perature is limited to four members, and, therefore, the fame of the Davy lamp to the smallest size that does not contain five, as generally supposed.

will emit white light before testing for gas, or, as he 3. That these four members have the boiling-points calls it, “ trying a fiery place.” When the atmosphere 80°, 110, 140°, and 170°. respectively; and, conse consists of a violently explosive mixture, one hears a quently, that the boiling-point difference in this series peculiar and sharp click, and observes a rapid combusfor an elementary difference of C,H, is 30° instead of tion of the gas within the wire gauze of the safety lamp: 220 and a fraction.

when the quantity of carburetted hydrogen is less, the 4. That the body obtained from coal-tar naphtha is flame of the lamp elongates ; and when the quantity is not identical with cumole from cuminic acid, as assumed very small, a peculiar lambent cap, of a bluish colour by Mansfield, nor even isomeric with it; but that it has is observed covering the flame of the lamp. These inthe formula which has been assigned to xylole, contain- dications can only be learnt by experience in the mines, ing C,H, less than that of cumole.

and when not properly attended to might give rise to 5: That the body obtained from coal-tar naphtha disastrous results. Should the atmosphere be explosive, boiling, at 1709 is quite a different body from cgmole the viewer or fireman lowers his lamp very slowly from oil of cumin, these bodies differing from each other and cautiously, until it has passed out of the explosive by C,H,

mixture, which usually occupies the upper part of the 6. That cumole from cuminic acid, and cymole from gallery of a mine, and travels in that position, notwithoil of cumin, do not even belong to the benzole series.

standing the law of diffusion. There are many well7: That the parabenzole of Church was in all pro- the Davy lamp in a quiet atmosphere, and where the

authenticated cases of explosions through the gauze of bability only a mixture of benzole and toluole.

lamps after the explosions have been ascertained to be in (To be continuod.)

good order.

A very ingenious instrument has recently been devised

for the detection and quantitative estimation of the ex. Formation of Nitrous Acid from Ammonia.—It plosive gases by Mr. G. F. Ansell, of the Royal Mint. The is well known that ammonia is decomposed by perman- instrument, which may be constructed in several different ganate of potash, and nitrogen evolved. It does not, forms, is based upon the well-known law in accordance however, appear to have been hitherto observed that a with which gases gradually mix with one another good deal of nitrous acid is formed at the same time. If through porous septa, and even through some materials the decolourised solution is filtered from the precipitated which do not appear to possess any interstices through hydrated peroxide of manganese, and slowly evaporated which the gases might pass. to dryness, a mixture of carbonate and nitrite of potash If a tube blown out into a cup at one end (Fig. 1), and is obtained. Abundant red fumes of nitrous acid will be bent in the form of the letter U be filled with mercury, so evolved from the residue on the addition of an acid. w. that the mercury stands in the cup, and the cup closed by a --Annal. der Chem, und Pharm., November, p. 256. piece of porous tile cemented on by a resinous varnish, a

FIRE DARIP

CHOK CAMP

the

Sabe set 1895 } Apparatus
for the Detection of Explosive Gases in Mines.

281 very serviceable indicator is obtained. On bringing this used instead of the glass vessel (6) 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. If the cup be filled with air and the

FIG. 2.
apparatus introduced into an atmo-
sphere 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 14'4 is 3.8, for every 1 part of
air which diffuses out of the cup 308
parts of hydrogen will pass in through
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 ele-
vation of the mercury in the open
limb will result. When the maxi-
mum effect has been produced, the
pressure within the cup will gra-
dually 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 atmosphere of a gas of greater density than the air.---as, for instance, carbonic acid, diffusion will take place, but the converse phenomena will be observed.

The specific 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 3.8-i.e., for every 4'7 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 ceveral 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 pulley, and counterbalanced on the opposite side, the taining

mercury in an inverted porous battery cell. The

been constructed by enclosing a U-tube with a bulb conrise and fall of the mercury causing the pulley to revolve and to indicate the alteration of pressure by the wood ; a small metal weight floats on the surface of the

edge of the cell is firmly cemented on to a piece of 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 Figure 3 is a section of a porous battery cell which is the level of the mercury in the tube, moves an index,

FIG. 4.

FIG. 3.

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