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Dr. FRANKLAND Suggested that the action might consist in the combination of the iodine with the hydrogen set free by the chlorine, the hydriodic acid being afterwards decomposed.

Dr. MULLER thought this was more probable than his original supposition, which had already been upset by further experiments.

The PRESIDENT remarked that reactions of this kind had been observed to take place in other cases, as, for instance, in the action of chloride of cyanogen on aniline. When this substance is exposed to the action of cyanogen itself a direct combination takes place; but with chloride of cyanogen he had found that a substitution compound was produced, the chlorine uniting with the hydrogen set free and forming hydrochloric acid.

It was announced that at the next meeting,
Mr. BLOXAM would read a paper, "On the Source of the
Arsenic in the Sulphuric Acid of Commerce, and on a Method
of preparing the same free from Arsenic."

THE following Address, to be presented to Her Majesty
on occasion of the death of the Prince Consort, was read
and adopted :-

TO THE QUEEN'S MOST EXCELLENT MAJESTY. May it please your Majesty,-We, the President, Council, and Fellows of the Chemical Society, beg permission to approach your Majesty and humbly express our great sorrow at the death of His Royal Highness the late Prince Consort, who during his life evinced a warm interest in the progress of the science to which our labours are devoted. We pray that the support and consolation of Almighty God may be vouchsafed to your Majesty under this bereavement, and that your Majesty may long continue to reign over a loyal and faithful people.

(Signed) A. W. HOFMANN, President.

MANCHESTER
LITERARY AND PHILOSOPHICAL SOCIETY.
Ordinary Meeting, January 7, 1862.

EDWARD SCHUNCK, Ph.D., F.R.S., Vice-President,
in the Chair.

Professor Dr. Johannes Gistel, of Kempten, in Bavaria; Federico Lancia di Brolo, Inspector of Studies in the University of Palermo; and James Nasmyth, Esq., C.E., were elected Corresponding Members of the Society.

A Paper was read by J. P. JOULE, LL.D., President, entitled, "Experiments on some Amalgams."

The weakness of the affinity which holds the constituents of amalgams in combination seemed to the author to offer the means of studying the relationship between chemical and mechanical force. His inquiries were extended to several amalgams, and gave results of which the following is a summary :

Amalgam of iron was formed by precipitating iron on mercury electrolytically. The solid amalgam containing the largest quantity of mercury appeared to be a binary compound. Iron does not appear to lose any of its magnetic virtue in consequence of its combination with mercury. Its amalgamation has the effect of making it negative with respect to iron in the electro-chemical series. The affinity between mercury and iron is so feeble that the amalgam is speedily decomposed when left undisturbed, and almost

immediately when agitated. The application of a pressure of fifty tons to the square inch drives out so much mercury as to leave only thirty per cent of it in the resulting

button.

Amalgam of copper.-By precipitating copper on mercury electrolytically, a mass of crystals is gradually formed. After a certain time the crystals begin to get fringed with pink, indicating uncombined copper. In this state the amalgam is found to be nearly a binary compound. On applying strong pressure to an amalgam containing excess of mercury, the latter is driven off leaving a hard mass composed of equivalents of the metals. If, however, the pressure be continued for a long time, the resulting amalgam contains more than one equivalent of copper, indicating a partial decomposition.

The Author gave an account of his experiments with amalgams of silver, platinum, lead, zinc, and tin. In the case of the latter amalgam, long-continued pressure drives off nearly the whole of the mercury, indicating in a striking manner the efficacy of mechanical means to overcome feeble chemical affinities.

Dr. ANGUS SMITH said: It is difficult to tell the exact limits of chemical and mechanical action, because they flow into each other. Let us call the attraction of surfaces a mechanical action, as it is not to our knowledge a chemical combination. Porous bodies exercise this to a very large extent, and yet do not produce chemical compounds. The amount is limited on one side by the pressure of the atmosphere. Chemical compounds are too powerful to be affected by such slight forces. Porous bodies or surfaces do not take up others in chemical equivalents so far as we know; the full capacity of saturation is not satisfied, because of counteracting influences. Water admits air very rapidly, but it is held so slightly that it is affected by atmospheric pressure, and even seems to follow exactly the atmospheric pressure; but a portion is held with such power that it is extremely difficult to remove, and is not ever removable by the mere removal of pressure as far as we know. The small affinity of the great mass or surface of water is equal to a great affinity for a small amount of air. All masses have more or less this mechanical action, but, as in the case of porous bodies, the attraction is feeble, and not raised into the power of a definite grasp of a given quantity such as an equivalent, which is the case with a powerful affinity forming a chemical compound. Large and watery masses lose their water slowly by the mere force of gravitation. Strong mechanical action rises to an equality with feeble chemical affinity. Weak chemical affinity sinks into an equality with mechanical action. Charcoal absorbs gases more eagerly under pressure, but by a removal of pressure they are still absorbed; so that the mechanical force is greater than the weight of the atmosphere can control. There are many cases in which these two forces, if they be two, meet. This of the mercury and other metal is one case. The feeble chemical affinity is, I suppose, overcome by the powerful mechanical force. The alloy with sufficient chemical affinity remains, that with a weak affinity separates. The mercury flows off following the law of liquids; in like cases it flows off like water flowing slowly from a moist porous mass like wet clay. Instances from the feeblest to the most powerful affinity might be given, showing that only when the power reached a definite point did the law of chemical equivalents come in. At the same time there is a definite point where surface action ceases under certain conditions.

These ideas have arisen partly from experiments on the subject, which may some day be published. I believe they explain the difficulties attending the attraction of masses which seem occasionally to oppose the combination by atomic weights.

A Paper was read "On the Conductibility of Heat by Amalgams," by Dr. F. CRACE CALVERT, F.R.S., and Mr. RICHARD JOHNSON.

The method followed in the investigations described in

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this Paper is the same as that detailed in their former Paper on the conductibility of metals and alloys.

In the first part of their Paper the authors treat of the conductibility of mercury, and prove that if the source of heat be applied at the upper part of a column of mercury, so as to prevent any motion of the solid molecules of the mercury, this metal becomes the worst conductor of all known metals; for, silver being 1000, mercury is 54.

In the second part of their Paper the authors examine the conductibility of the solid and semi-solid amalgams prepared in equivalent quantities of pure metals with mercury, and they show that amalgams may be divided into two classes-those containing an excess of equivalents of the amalgamated metal, and those which on the contrary contain an excess of equivalents of mercury. The first class conduct heat at the mean rate of the two metals composing the amalgam, and in accordance with the calculated result, as shown by the following table :

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Jan. 25, 1862.

badly, that of zinc, which was perfectly fluid and free from crystals, conducted heat very freely. As they pur sued their researches they found these views to be in correct, for the amalgam of bismuth, a very crystalline one, conducted heat with great facility.

Having observed that tin affected the fluidity of mercury in a most remarkable manner, so that even the one hundred thousandth part of that metal would interfere with the property which mercury has of assuming easily a globular form, they prepared the following series of amalgams of tin :—

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99'50+ ", 19.30 0'50 This table proves that up to 175 the conductibility of Found. Calculated. mercury remains constant, when by reducing the tin by 4th of the conductibility of the amalgam is doubled; by further abstracting one-third of the tin the conductibility is again doubled.

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The second class, comprising those amalgams containing an excess of mercury, conduct heat as if they contained no other metal, although its proportions may vary from 10 to 34 per cent.

These interesting results were confirmed by observing amalgams of tin, zinc, bismuth, copper, lead, and silver, and applying the source of heat in all cases at the upper part of a perpendicular column of the amalgam.

The third part of their Paper has reference to the conductibility of mercury when mixed with two per cent. of various metals, and when the heat is applied at one end of a horizontal column; and they have obtained the following interesting series of results :Found. Calculated.

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NOTICES OF PATENTS.

870. Combustion of Fuel for Generating Steam. W. H. PHILLIPS, Nunhead. Dated April 9, 1861. THIS invention relates to the employment of steam in the place of atmospheric air or other gases for the purpose of supporting the combustion of fuel, and generating heat in furnaces or fireplaces of suitable construction.

The ultimate products of combustion are identical, whether air alone or the same mixed with aqueous vapour be admitted to the burning fuel; the equivalent of heat disengaged must therefore remain constant under the varying circumstances. There are, however, certain practical considerations which are likely to declare in favour of the employment of steam; such, for instance, as the cooling of the furnace bars, and the more rapid generation of inflammable gases in the midst of the burning fuel.

876. Apparatus for Receiving, Drying, and Deodorising Human Excrement. F. TAYLOR, Romsey. Dated April 9, 1861.

THIS proposal refers to certain mechanical contrivances for separating and collecting the liquid and solid fæcal products, and for drying the latter in situ with the aid of a powerful current of air.

894. Obtaining Ammoniacal Salts and other Valuable Products from Liquors or Substances Containing Ammonia, C. N. KEKNOT, Gloucester House, West Cowes; and M. D. RUCKER, Fenchurch Street, London. Dated April 11, 1861. (Not proceeded with.)

IN carrying out this invention it is proposed to mix the liquor in a tank or other suitable vessel, with crude sulplate of zinc, or other sulphates, or a liquid specially prepared by acting on animal or mineral substances with diluted acids, the object being to produce gelatinous precipitates; or the ammoniacal liquor may be passed through filters containing the sulphates or the preparation already referred to.

The aim of this specification appears to depend on the employment of a gelatinous precipitate for the purpose of absorbing and thus concentrating the free ammonia contained in dilute gas liquors, &c. The compounds derived

NEVE

from the zinc salts are, however, all or mostly of a soluble nature (the oxide of this metal being easily dissolved by ammoniacal salts), and consequently are ill-fitted to perform the function here required to be exercised by the chemical agent.

Grants of Provisional Protection for Six Months. 2293. Marc Antoine Francois Mennons, Rue de l'Echiquier, Paris, "An improved apparatus for the conveyance of medicinal substances into various parts of the human body."-A communication from Salvator Vinci, Rue de la Pepinière, Paris.-Petition recorded September 14, 1861. 3092. William Ford Stanley, Great Turnstile, Holborn, London, W.C., "The use of aluminium for the construction of mathematical instruments used for geometrical drawing, surveying, and nautical purposes, and improvements connected therewith."-Petition recorded December

10, 1861.

3105. Joseph Schloss, Cannon Street, London, "An improvement in forming the leaves of albums and books for containing photographic portraits and views."A communication from Simeon Schloss, Paris.

3109. John Potter, Leeds, Yorkshire, "An improved mode of jointing or connecting telegraph wires, which is also applicable to jointing or connecting signal wires, fencing wires, and other wires or rods."-Petitions recorded December 11, 1861.

3116. Robert Mushet, Coleford, Gloucestershire, "An improvement or improvements in the manufacture of iron or puddled steel."

CORRESPONDENCE.

Manufacture of White Lead.

To the Editor of the CHEMICAL NEWS. SIR,-As a general painter I use a considerable quantity of white lead, which for many years I have bought in the ground state, I mean ground with linseed oil, and in this condition I have mostly found it very coarse in texture, and more or less adulterated with carbonate or sulphate of barytes. If purchased in the dry state it is seldom adulterated, I have, therefore, of late, obtained it in this condition and ground it with oil myself, and here is my difficulty-how to get it fine.

All the dry carbonates of lead I have been able to obtain from some of the best manufacturers have been of a very hard and gritty nature, and when mixed with oil, a very large amount of grinding is necessary to reduce it to the required smoothness, although ground under heavy stones with steam power. The ground lead sold by most makers is much coarser than desirable, and if spread out with the palette knife appears something like a sheet of very fine sand-paper-quite a granulated appearance.

Can any of your readers inform me how I may treat the dry carbonate, so that when mixed with oil it may be easily ground into a smooth mixture? I recollect years ago I did obtain, from an old London house, dry lead, which, with the palette-knife only, could be readily mixed with linseed oil into a smooth, butter like mixture, without the least granulated form; but the leads now manu"Im.factured will not do so unless they are improved by being could be informed how to soften the carbonate of the well levigated in water before being ground in oil. If I manufacturers for grinding in oil, with less of this levigation, or without it altogether, I should be obliged. I am, &c. A SUBSCRIBER.

3138. Thomas Killingworth Adkins, Wallingford, Berk. shire, and John Bonthron, Regent Street, London, provements in the manufacture of starch, and in apparatus employed therein."

3141. Richard Archibald Brooman, Fleet Street, London, "Improvements in blowers or apparatuses for superheating steam and other gases, and for projecting them, combined with atmospheric air, upon ignited combustible matter."-A communication from Felix Alexandre Testud de Beauregard, Paris.- Petitions recorded December 13, 1861.

3143. Jacques Edouard Duyck, Tutsham Mills, West Farleigh, Kent, "Improvements in the expression of oil from cake and seeds, and in apparatuses employed therein." 3147. William Elliott Debenham, The Terrace, Kensington Gardens Square, London, "An improved plateholder for photographic purposes."

3148. William Husband, Hayle, Cornwall, "An improved water safety-valve."

Notices to Proceed.

2123. George Nye, Mount Street, Lambeth, London, "Improvements in apparatus for administering injection in a continuous stream, also applicable as an eye-douche, and other purposes."

2142. Benjamin Browne, King William Street, London, "An improved process and apparatus for concentrating ores or tailings, or separating pulverised mineral substances of different kinds or qualities from each other." -A communication from Henry Eberhard Roeder, Broadway, New York, U.S.-Petitions recorded August 28, 1861. 2159. Alexandre Jaille, Agen, Lot et Garonne, France, "An improved manufacture of manure."

2161. Henry William Spencer, Stepney Causeway, Commercial Road, London, "Improvements in the manufacture of animal oils, the said improvements relating more particularly to the processes of refining them to be used for lubricating purposes."

2213. Frederick Bennett, Upper W shire, "An improved method of surface of lead and lead composition alloys."-Petitions record

Chemical Notices from Foreign Sources.

1. MINERAL CHEMISTRY.

Vierteljahressch., Bd. x.
Colour of Water.-Wittstein publishes (Wittstein's
colour of water.
s. 342) a long memoir on the
He establishes-1. That pure water is
not colourless but blue. 2. That the mineral matters
which a water may contain do not affect the colour.
3. That the variety of colour in water depends more on
the organic matter in solution. 4. The organic matter is
held in solution by an alkali. 5. The amount of organic
matter in solution depends solely on the amount of alkali.
6. The smaller the amount of organic matter the less is
the colour removed from blue: as the organic matter
increases the colour goes from blue to green, and eventually
to brown. 6. Periodical changes in the colour of the
same water do not depend on changes in the organic con-
stituents, but on rest and atmospheric appearances. 7. It
may be universally accepted as a rule that the browner a
water is the softer it is; and the nearer the colour
approaches blue the harder it is. The difference does
not depend so much on the amount of organic ingredient,
as on the amount of alkali. There is nothing very new in
this. Experienced water testers have for some time judged
or guessed the amount of organic matter from the colour

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II. ORGANIC CHEMISTRY.

ew Derivative from Benzoic Acid.-SchutzenAnd Sengenwald (Comptes Rendus, t. liii. p. 974) amined the brown product, which is obtained henzoic acid is prepared by passing a current of 14 into a lution of benzamic acid. They I disso in alkalies and formed brown, lts, the solutions of which gave

56

Miscellaneous-Answers to Correspondents.

brown amorphous precipitates with most metallic salts. Their analysis led the authors to the conclusion that the brown body is a bibasic acid, which they propose to call benzulmic acid. Its production at the expense of oxybenzoic acid is explained by the following equation :

2 (C14 Hε O6) + 2 NO3=2 HO + C28 H10O12 + 2 NO2.

III. TECHNICAL CHEMISTRY.

Preparation of Arseniate of Soda.-Dr. Aug. Streng gives (Chemisches] Central Blatt, No. 54, 1861, s. 852) some researches he has made on the preparation of monobasic arseniate of soda for technical purposes. He concludes that the best process for obtaining this salt on the large scale is to heat together 30 parts of nitrate of soda, and 37 parts of arsenious acid, at first gently for 6 to 9 hours, and then raise the temperature for the same time. The mass should be allowed to cool slowly. The product has not exactly the theoretical composition of monoarseniate of soda, but the salt answers well for practical purposes. Only about 4 per cent. of arsenious acid is left. New Way of Producing Local Anæsthesia.—

M. Fournié has employed very successfully a mixture of glacial acetic acid and chloroform to produce local anæsthesia (Comptes-Rendus, t. liii. p. 1066). He puts a mixture of equal parts of these bodies into a conveniently shaped glass vessel, holds this in his warm hand, and applies the mouth of it to the part to be rendered insensible. In about five minutes, he says, complete insensibility, which extends to some depth, is produced. Of course the method can only be applied when the skin is sound; and if we wanted an abscess opened we would certainly give it a trial.

MISCELLANEOUS.

Royal Institution. The following Lectures will be delivered in the ensuing week :-Tuesday, January 28, • at three o'clock, John Marshall, Esq., "On the Physiology of the Senses." Thursday, January 30, at three o'clock, Professor Tyndall, "On Heat." Friday, January 31, at eight o'clock, William Hopkins, Esq., "On the Theories of the Motions of Glaciers." Saturday, February 1, at three o'clock, Rev. A. J. D'Orsey, "On the English Language."

CHEMICAL NEWS,
Jan. 25, 1862.

sale of the black in its pure state only, and, as it was not alleged that Board had mixed it with the cement fraudulently, or to evade payment, that the plaintiff was not entitled to recover. The rule must therefore be discharged.-Rule discharged accordingly.

American Chrome Iron Ore.-Asbestos Paper. - We have received from a correspondent in Baltimore, Mr. Oudesluys, of South Gay Street, an excellent sample of the chrome-iron of that locality. It occurs in the form of small black lustrous granules, many of which, under magnifying power, appear to be regular octahedrons. There is no appreciable quantity of magnetic oxide of iron intermixed with the sample, nor of other impurities which would tend to lower the per centage of sesquioxide of chromium. The amount of this latter constituent as determined by Dr. Genth, is stated to be equivalent to 63 per cent. of chromic acid-a mode of expressing the value of the ore by the quantity of chromic acid produced on fusion with an alkali, and not that of the green sesquioxide actually contained therein. By a qualitative examination we have ascertained that the proportion of chromium must certainly be very large, and have had at the same time an opportunity of corroborating a statement made by our informant to the effect that the mineral requires longcontinued fusion to separate the whole of the chromium in a soluble form. Ore of this superior description may be obtained in casks ready for shipment at the rate of about one dollar for each one per cent. of chromic acid per ton, and in quantities of about 200 tons annually. It is, however, considered more judicious to work this ore in admixture with other qualities which are produced in greater abundance, -1500 tons annually, the average composition of such samples furnishing usually about 50 per cent. of chromic acid. The ore last described was accompanied by specimens of asbestos, and of paper containing about one-third proportion of the same. The mineral may be procured from Mr. Oudesluys at the rate of 14 cents per pound,-a low price considering the high quality of the article offered. The specimen sent is beautifully white, and the fibres are long and delicate. It has been tried in America for papermaking and for the manufacture of steam-packing, in both of which applications it is said to be very serviceable. Its property of resisting heat and its bad conducting power would render this material particularly valuable in connection with steam machinery. The sheet of paper sent is a portion of an experimental manufacture; it burns with flame, leaving a white incombustible residue, which, with careful management, retains the form of the original sheet, the weight of ash amounting precisely to 30 per cent. Characters written on the paper with ordinary black ink are still legible after burning.

-

ANSWERS TO CORRESPONDENTS.

All Editorial Communications are to be addressed to the EDITOR; the Office, 1, Wine Office Court, Fleet Street, London, E.C.

Manufacture of Cement.-The following case, heard at the Court of Common Pleas before Lord Chief Justice Erle, on Tuesday the 14th inst., possesses interest from the circumstance that it refers to an unsuspected ingredient in builders' cement :-Fulwood versus Akerman and another.-The plaintiff was a cement manufacturer, and the defendants were executors of one Board, who owned quarries near Bridgwater. In 1849, the plaintiff having discovered a method of burning shale, and thereby making a bituminous powder, which was valuable in the manufacture of paint, ink, &c., disclosed his secret to Board, and entered into a contract with him to share the profits which should arise from the manufacture in Board's quarries of the article, which they denominated "Imperial and Advertisements and Business Communications to the PUBLISHER at Russian Black." After some time Board discovered that he could make a greater profit of the black by employing it in colouring cement than in selling it in its simple state. He, thereupon, ceased selling it in its pure state, mixed it with cement, and sold the cement in large quantities. The plaintiff then claimed his moiety of the profits on the sale of the black so sold in cement, as well as in its pure state. Board and his representatives refusing to pay this, the plaintiff brought the present action. In the course of the case it appeared that a previous action between the parties had been disposed of in 1853, and that although the plaintiff was aware that Board was mixing the black with cement, he made no claim then, nor till he brought the present action. The Court were of opinion that the agreement between the parties contemplated a division of the profits arising from the

Vol. IV. of the CHEMICAL NEWS, containing a copious Index, is now ready, price 128., by post, 12s. 8d., handsomely bound in cloth, goldlettered. The cases for binding may be obtained at our Office, price 18. 6d. Subscribers may have their copies bound for 28. if sent to our Office, or, if accompanied by a cloth case, for 6d. A few copies of Vols. I. II. and III. can still be had. Vol. V. commenced on January 4, 1862, and will be complete in 26 numbers.

J. V. We will bear your several requests in mind.

A. B. P.-It is not too late, such matter is always interesting. We shall be glad to receive the abstracts alluded to.

A. P. See the "Chemistry of Calico Printing," noticed in our
Second Volume, p. 214.

F. W. Primrose.-We cannot give the address. Apply to Mr. B.
Woodcroft, Patent Office, Southampton Buildings.
exhibited the specimen would obtain the desired information. Direct
A Subscriber.-Probably a letter addressed to the gentleman who

to the Society.

THE CHEMICAL NEWS.

VOL. V. No. 113.-February 1, 1862.

SCIENTIFIC AND ANALYTICAL CHEMISTRY.

Remarks on M. Stas's Researches on the Relations Existing between Atomic Weights, by M. MARIGNAC. AFTER passing an eulogium on M. Stas's meritorious work, Professor Marignac urges the following considerations:

He thinks the final conclusions of M. Stas too absolute. He will not be convinced of the exactness of the determination of an atomic weight; or, rather, he cannot entertain a clear idea of the degree of confidence to be reposed in it, only when the weight has been obtained by several perfectly independent methods, and determined by an analysis of several distinct compounds. Thus, M. Marignac expresses a wish that M. Stas-who obtained 107.943 and 107.924 for the equivalent of silver as the mean of each of two series of experiments-should analyse, with his usual care, salts of silver with organic acids. M. Marignac adduces the fact that in 1846 he arrived at the number 107.968 for silver by the latter method. Perhaps other methods will be found, showing whether the differences between the results furnished by the various methods are really less than the differences between these results and those of the calculation founded on Prout's hypothesis.

According to M. Marignac it is necessary for the settlement of the question to study, by analysis and synthesis, perfectly distinct compounds, and not to be satisfied with experiments differing only in the manner the same compounds are made to react.

When M. Stas sets forth, as a control of the synthesis of nitrate of silver, the experiments by which he determined the proportional relation between this salt and chloride of potassium, M. Marignac sees in this only a proof of the exactness of the experiments themselves, but not a control of the experimental method. For instance, let it be supposed that nitrate of silver, prepared in the most accurate manner, does not contain its elements in the rigorous proportions of their atomic weights, then the most exact methods applied to its analysis or synthesis, will only give, with the same degree of inaccuracy, the relation of these weights.

To develope his ideas on this subject, M. Marignac cites his own experiments on monohydrated sulphuric acid. He shows, in fact, that this compound, hitherto considered so stable, is, on the contrary, very unstable. It is only when it contains a slight excess of water (about 1 per cent.) that it becomes perfectly stable; otherwise, the slightest elevation of the temperature induces a disengagement of vapours of anhydrous sulphuric acid.

Who can affirm à priori that sulphide or nitrate of silver is incapable of retaining, at a high temperature, a small quantity either of sulphur or nitric acid, when sulphuric acid can retain a slight excess of water at above 100°?

Causes of error of this kind, to which others might be added, prevent M. Marignac from being convinced that the discrepancies between experiment and Prout's law cannot be explained by the imperfection of experimental methods.

Even admitting that these objections are groundless, M. Marignac urges a second consideration, preventing his concluding, with M. Stas, that Prout's law is nothing better than a delusion, and that simple bodies are necessarily distinct entities.

If M. Stas's numbers do not exactly coincide with those of Prout, at least they so nearly approach them that this fact cannot be regarded as accidental. The remark made on the laws of Mariotte and Gay Lussac, relative to the variations of the volume of gases, is applicable to the laws of Prout. These laws, long considered absolute, have been found inaccurate when examined with the degree of accuracy attained by MM. Regnault and Magnus. Nevertheless, they will always be considered as expressing the natural laws, whether from a practical point of view-for, in most instances, they allow a sufficiently approximative calculation of the changes in a volume of gases-or even from a theoretical point of view; for they very probably express the normal law of these changes in the volume, allowance being made for several disturbing influences to which we perhaps return further on to calculate the effects. It may well be believed that this is likewise the case with Prout's law.

M. Marignac concludes with an important observation due to the illustrious and sagacious chemist who drew attention to these interesting questions:-"The fundamental principle which led Prout to propound his law

that is to say, the idea of the unity of matter, and all the more or less brilliant conceptions based upon this principle-are altogether independent of the size of the elementary atom, which would serve as a common divisor of the weight of simple bodies, and which may, consequently, be considered as expressing the weight of atoms of primordial matter. Let this weight be that of an atom of hydrogen, or half or a quarter of an atom, or an infinitely smaller fraction of one, these considerations would not the less retain the same degree of probability. The result would simply be less simple

relations of constitution between the various elements."

On the Formation of the Topaz and the Zircon,
by M. H. SAINTE-CLAIRE DEVILLE.

IT is sometimes possible, during laboratory experiments, to foresee the mode of formation of certain kinds of minerals; but our conclusions cannot be perfectly exact unless we can show that the efficient physical and chemical circumstances are adequate not only to account for the formation of the minerals, but are essential for their production. This happy degree of certainty is not often attainable, but in some cases it is very nearly approached; as, for example, with topaz and zirconium.

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