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{CHEMICAL NEWS,

January 31, 1879,

the hydrate of trimethyl-sulphine. On evaporating the | Catalogue of Chemical Apparatus and Pure Chemicals solution of the salt on the water-bath it begins after a time to crystallise out. On leaving the saturated solution to cool a large quantity of clear cubical crystals were obtained. These are not hygroscopic, insoluble in hot alcohol, and without any smell of sulphide of methyl. These properties prove it to be one of the most stable of the salts of trimethyl-sulphine. Analysis agrees with the

formula

per cent.

[(CH3)3S12S2O6.H2O.

On heating the salt to about 120° water is given off. On raising the temperature to 220 sulphurous acid is given off, and afterwards along with it sulphide of methyl, and the salt froths and melts. The heating at about 200° was continued until very little gas was given off. 8:015 grms. were found to have lost 3.325 grms., equal to 414 On cooling the liquid solidified. The crystalline mass was very hygroscopic, and dissolved in alcohol. On adding ether to the alcoholic solution the substance was precipitated as an aqueous syrup, and on standing over sulphuric acid crystallised out in beautiful long fine prismatic needles. The presence of the trimethyl-sulphine radical was proved by double decomposition with iodide of potassium, when the iodide of trimethyl-sulphine crystallised out. The presence of methyl-sulphuric acid was also proved, These results, along with estimations of carbon and hydrogen, prove the substance to be the methyl-sulphate of trimethyl-sulphine. The decomposition of the dithionate is therefore expressed by the following equation: :

(CH3)3) S206.H2O= (CH) SO4+ (CH3)2S+H2O. (CH3)3S)

A paper was also read by Mr. J. W. DRAKE on the "Constitution of Inorganic Salts."

NOTICES OF BOOKS.

Useful Information on Practical Electric Lighting. By KILLINGWORTH HEDGES, C.E., M.I.M.E.

con

A POPULAR account of the principles, production, working, and in part the cost of the electric light, confessedly somewhat hastily thrown together. Mr. Hedges divides his subject into nine sections. The introduction treats of the laws governing induced magnetic currents; the second chapter of the various kinds of electrodes and electric lamps; the third is on the division of the electric light. The kind and quantity of power required are sidered, as well as the application of the light for illumination. The transmission of electricity by wires is then explained, the approximate cost of working is necessarily somewhat incompletely dealt with, trustworthy data being as yet wanting. Mr. Hedges, speaking as a practical engineer, very properly ridicules the nonsense that has been written respecting the extinction of gas by electricity. The same prophecies were made with regard to oil and candles when first gas was used. The electric light, says Mr. Hedges, will educate the public to a higher degree of artificial lighting, a prophecy already fulfilled by the Phoenix Gas Company, which has lighted up the bridge end of Waterloo Road with a brilliancy hitherto unknown in the history of gas lighting. A higher standard of gas will be called for by shopkeepers, and an increased, instead of a diminished, consumption of gas will follow. We cannot, however, agree with Mr. Hedges when he thinks that we may obtain the electric light more economically from the battery than from the dynamo-electric machine. Mr. Hedges promises to give us a second edition of his pamphlet. In the present edition he has been continually betrayed into the use of technical expressions which, although perfectly familiar to all scientific men, will be simply so much Sanscrit to the ordinary reader.

A WELL compiled illustrated catalogue of every description of chemical and physical apparatus. We would especially direct the attention of students, teachers, lecturers, and medical officers of health to the cheap sets of scientific apparatus described at the end of the book, which seem to be a speciality of this old-established firm. There is an excellent index at the end of the catalogue.

Practical Physics, Molecular Physics, and Sound. By FREDERICK GUTHRIE, Ph.D., F.R.SS.L. and E., Professor of Physics in the Royal School of Mines. London: Longmans and Co., 1878.

THIS little work belongs to the excellent elementary series called the London Science Class Books now in course of publication by Messrs. Longmans. The arrangement adopted by Prof. Guthrie is somewhat new. After explaining the principles of molecular cohesion in the case of solids, liquids, and gases he carries his pupil through diffusion, effusion, osmose dialysis, and vortex motion, into wave motion in general, and lastly introduces him to the principles of sound, thus rendering the sequence complete, the string telephone and the phonograph being introduced as illustrations. There is a useful appendix added explaining the use of the vernier, the method of making parchment paper, hints on glass working, barometer making, &c. The experiments illustrating the lessons in the body of the work, and the apparatus and materials used in performing them, are also explained at greater length in a second appendix.

Notes of Statutes and Legal Decisions Affecting the Public Health Act, 1875, from 1875 to 1878. By J. V. VESEY FITZGERALD, B.A. London: Longmans and Co. THESE notes are intended by the author as a sequel to a former work on the same subject at the time of the passing of the Public Health Act of 1875. To officers of health, inspectors of nuisances, factory inspectors, medical men, local boards, vestries, and all other bodies or indivarious health acts are duly carried out, this little work viduals whose duty it is to see that the provisions of the will prove invaluable.

The Retrospect of Medicine. Edited by W. Braithwaite, M.D., and JAMES BRAITHWAITE, M.D. Vol. lxxviii., July to December, 1878. London: Simpkin, Marshall, and Co., 1879.

As usual there is but little to interest the chemist in the present volume of Braithwaites' "Retrospect," valuable as it may be from a purely medical point of view. A Dr. Jencken, who hails from the Emerald Isle, recommends gun-cotton as a dressing for wounds on account of the antiseptic character of the acids used in preparing it. We should imagine that properly washed pyroxylen would have no greater antiseptic power than ordinary cleaned cotton-wool, while if it still retained sufficient traces of acid to possess antiseptic properties it would be a highly dangerous addition to hospital requisites. Of quite a different calibre is Mr. Spencer Wells's warning to surgeons-not too place to much confidence in the use of antiseptics in surgical operations at the risk of omitting any of the precautions which experience has declared to be necessary; in a word, antiseptic treatment must not be looked upon as a substitute for measures which have already proved effectual, but only as an additional safeguard. Sir Henry Thompson gives an account of the use of the microphone in sounding for stone (July, 1878), but his experiments at present do not seem to have led to any practical result. The use in psoriasis of crysophanic acid, one of the few chemical remedies discovered of late years, appears to be spreading. By the way, we may mention that a cheap method of preparing this acid

NEWS

di Papa, near Rome, he had been able to distinguish three kinds of sounds, and to trace their relation with the movements of his seismometers.

Harmotome and Stilbite.-A. Gaudin.-The author

gives diagrams to show the atomic arrangement of these minerals.

Electrochemical Action under Pressure. - Á. Bouvet. The author considers that he has established

is a desideratum. It is related to anthracen, being convertible into that substance when heated with zinc-dust, the contrary operation, therefore, ought not to be impossible. The only other papers of chemical interest are those of Dr. Ogston, Jun, "On a Stale Solution of Ammonium Sulphide as a Test for Chloral; "On Butylchloral," by Liebreich, who finds that whereas in the case of ordinary chloral hydrate the heart is paralysed before the respiratory organs, the reverse held good in the case of butyl-chloral, a very singular and important physiolo- the two following laws:-That the decomposition of water gical observation; and "On the Advantage of Oxygen by a current is independent of pressure. The quantity of Inhalation in Cases of Asphyxia from Breathing Carbonic electricity necessary to decompose a given weight of water Acid." Dr. R. H. Goolden announces that for thirty-five is the same under whatever pressure the decomposition years he has used manganese sulphate with great success in the treatment of liver complaint, but that a prejudice Liquefaction of Gases by MM. Cailletet and Pictet. exists against its use on account of the difficulty of getting-A. Bouvet.-The writer points out that the principle it dispensed, pharmaceutists either never having the salt made use of was indicated by him in a memoir addressed in stock or taking manganesiæ sulph. for magnesia sulph., to the Academy on October 8, 1877. and dispensing it accordingly. Dr. Goolden's efforts to introduce this remedy deserve all praise, in spite of the little success that he has hitherto met with. The same remark applies to Dr. B. W. Richardson's endeavours to introduce the alkaline ethylates as caustics.

CORRESPONdence.

INFLUENCE OF CHLOROFORM ON
NITRIFICATION.

To the Editor of the Chemical News. SIR,-In reply to Mr. Warington's letter, I must at once acknowledge that I used the term "nitrification" in a stretched and, I fear, erroneous sense. I certainly am of opinion, that in many cases" the destruction and production of nitrates are allied phenomena, both of which are due to the action of bacteria "or of similar organisms. Perhaps even one and the same organism induces both the formation and (under different circumstances) the reduction of nitric acid, and both these actions I included in the term "nitrification," precisely as we consider both the decomposition and the formation of carbonic acid by plants as evidences of the growth of the plant, although in reality the excretion of carbonic acid is rather a sign of decay than of increase.

When I stated that nitrification was not arrested by small quantities of chloroform I meant, and ought to have said more clearly, that chloroform is not necessarily a poison to organisms allied to, or identical, with that producing nitric acid.—I am, &c.,

OTTO HEнner.

CHEMICAL NOTICES FROM FOREIGN

SOURCES.

is effected.

Magnetic Rotation of the Plane of Polarisation of Light under the Influence of the Earth.-J. Joubert -The author admits the reclamation of H. Becquerel concerning the experiment described in his memoir of December 23.

Use of the Telephone and Microphone in Scientific Researches.-M. Hughes.-These instruments may be advantageously employed, especially in researches concerning very feeble induction-currents resulting from the movement of a magnet before a helix.

A New Electric Lamp.-E. Ducretet,-The arrangement of the lamp cannot be described intelligibly without the accompanying figure. Its principal peculiarity is the use of a mercurial column into which the points are plunged.

Existence of an Oxide of Nickel, Ni304.-H. Baubigny. This oxide, unlike the corresponding iron compound, is not magnetic. It is formed on treating nickel chloride at 440° with moist oxygen, and appears as a grey metallic crystalline powder. It is slowly attacked by hot hydrochloric acid with liberation of chlorine, and at a strong heat it is reduced to protoxide, losing 6.6 per cent of its weight.

Nitrates found in Beets and in some other Roots. -J. A. Barral.-The highest percentage of nitrates calculated on the dry matter is found in the roots poorest in sugar.

Inactivity of the Chrome Compounds in Comparison with Vanadium in forming Aniline-black by means of Aniline Salts in Presence of Chlorates.G. Witz.-The author, with reference to the memoir of M. Grawitz (Comptes Rendus, lxxxvii., p. 844), declares that the salts of chrome cannot be used in place of the salts of vanadium in their action upon aniline salts in presence of chlorates. The presence of chrome seems even slightly injurious.

Analysis of Crude Sugars and Saccharine Matters. Determination of Water and of the Totality of Salts with Mineral Bases and Organic Acids.-E. Laugier. -The author determines moisture by desiccation in

NOTE.-All degrees of temperature are Centigrade, unless otherwis hydrogen, or in coal-gas previously purified and dried. expressed.

The total mineral bases are determined by incineration in a current of oxygen at temperatures below the melting

Comptes Rendus Hebdomadaires des Séances, l'Académie de point of chlorides. In a second portion of exactly double

des Sciences. No. 27, December 30, 1878. Reply to M. Berthelot.-M. Pasteur.

Observations Conncering M. Pasteur's Communication.-M. Trécul.-A continuation of the controversy springing out of the posthumous work of Claude Bernard. The Microphone in Subterranean Research.-M. d'Abbadie. The speaker, in presenting to the Academy a work by M. Michel de Rossi "Il Microfone nella Meteorologia Endogena," remarked that the author had successfully applied the microphone to the study of underground movements, and that at his observatory at Rocca

the weight the organic acids are extracted with ether according to Schloesing's method and half the ethereal extract is poured to the ash obtained by the former experiment, thus re-constituting the previously existing salts. The mixture is again dried in the stove as in the determination of water and weighed. The second half of the ethereal extract is then neutralised with a standard alkaline liquid. From the result obtained is calculated the weight of the carbonic acid equivalent to the organic acids. By deducting from the weight of the salts that of the ash, less the weight of the carbonic acid expelled, we obtain the weight of the total organic acids, and of the

54

Chemical Notices from Foreign Sources.

water which their salts retain at the temperature adopted for desiccation.

Innocuity of Borax Employed in the Preservation of Food.-E. de Cyon.-The author asserts that food thus prepared preserves all its nutritive value.

Berichte der Deutschen Chemischen Gesellschaft zu Berlin,

No. 13, 1879.

Action of Dehydrating Agents upon Anhydrous Acids (Fifth Memoir).-S. Gabriel and A. Michael.-The authors examine the behaviour of phthalyl-propionic acid with sulphuric acid and with sodium amalgam; of ammonia with desoxy-benzoin-carbonic acid; and of sodium acetate with a mixture of anhydrous phthalic and isobutyric acids.

Determination of Vapour Densities.-A. W. Hofmann. The author has been engaged with a course of experiments in order to ascertain the limits within which the determination of vapour densities in a barometric vacuum is usefully practicable. He describes a modified method for the expulsion of air, but purposes giving on a future occasion a detailed account of his methods and results.

The Formation of Methyl-aldehyd.-A. W. Hofmann. -The author passes a mixture of the vapour of methylic alcohol and of air through a platinum tube, not too narrow, containing a bundle of fine platinum wires. On the application of a gentle heat and condensing the vapours methylic aldehyd is obtained in quantity.

La Correspondance Sccientifique.
December 10, 8781.

|

{CHEMICAL NEWS January 31 18:9.

Lake Nyassa, with Notes of a Recent Expediton through that Country by H. B. Cotterell. March 18, "Some Remarks upon anOld Map of Africa contained in Janson's Atlas, published at Paris in 1612," communicated and exhibited by R. Ward. April 1, "The Contact of Civilisation and Barbarism in Africa, Past and Present," by Edward Hutchinson, Lay Secetary of the Church Missionary Society. Cantor Lectures-First Course, on "Mathematical Instru

ments," by W. Mattieu Williams. The remaining two

lectures will be delivered

on the following dates:

January 20 and January 27. The second course will be by Dr. W. H. Corfield, M.A., on "Household Sanitary Arrangements." It will consist of six lectures, to be given on the following dates:-Febuary 17, 24, March 3, 10, 17, 24. The Third course will be by W. H. Preece, on "Recent Advances in Telegraphy." It will consist of five lectures, to be given on the following dates:-April 21, 28, May 5, 12, 19. Additional Lectures-A Course of two lectures will be given by Dr. B. W. Richardson, M.A L.L.D., F.R.S., on "Some Further Researches in Putrefactive Changes," in continuation and completion of his course of Cantor Lectures given last session. Any addiitions to or alterations in the above meetings will be duly announced.

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The Patent Office at Washington has refused to grant Mr. Edison a patent for his electric light, as his invention is merely a reproduction of that of Mr. Starr, of Cincinnati, whose patent dates from 1845. The English Patent Office is also said to have found Mr Edison's invention to have been anticipated by that of Chanzy, of Brussels, in, WEDNESDAY, 1852 laid by him before the Academy of Sciences Febuary 25th 1858.

Syrup of orgeat is made of glucose made into an emulsion with oil and gum-tragacanth and flavoured with nitrobenzol.

The tin-paper used for covering chocolate and other esculents has been found to contain 85 per cent of lead.

MISCELLANEOUS.

Royal Institution, 3.

Prof. Schäfer.

Zoological. 8.30.

"Animal Development,"

Society of Arts. 8. "The Opening of the District
to the North of Lake Nyassa, with Notes of a
Recent Expedition through that Country," by H.
B. Cotterell.

5th.-Society of Arts, 8.

"The Best Method for Im

proving the Condition of the Blind," by Dr. T. R. Armitage.

Geological, 8.

Pharmaceutical, 8.

THURSDAY, 6th.-Royal, 8.30.1

Royal Institution, 3. "Electric Induction," J. H.
Gordon.

Chemical, 8.

Discussion on Dr. Tidy's Paper on

the Processes for Determining the Organic Purity of Potable Waters.

Royal Society Club, 6.30.

London Institution, 7.

FRIDAY, 7th.-Royal Institution, 9. "Bells," by Rev. H. R. Haweis.
Geologists' Association, 8. (Anniversary.)

Macan

SATURDAY, 8th.-Royal Institution, 3. "Lessing," by Reginald W.
Physical, 3. (Anniversary.)

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Society for the Encouragement of Arts, Manufactures, and Commerce, John Street, Adelphi, London, W.C.-One hundred and twenty-fifth session, 1878-79-The following arrangements have been made for the forthcoming meetings of the Society:-Ordinary Meetings-Feb. 5, The Best Methods for improving the Condition of the Blind," by Dr. T. R. Armitage. Feb. 26, "Indian Pottery at the Paris Exhibition," by George Birdwood, M.D., C.S.I. March 5, "The Social Necessity for Popular and Practical Teaching of Sanitary Science," by Joseph J. Pope, M.R.C.S., L.S.A. March 12, "The Compensation of Timekeepers," by Edward Rigg, M.A. March 19, "Economical Gardens for Londoners," by W. Mattieu Williams, F.R.A.S., F.C.S. March 26,"The Treatment of Iron to Prevent Corrosion" (a second communication), by Prof. Barff, M.A. In the Chemical SectionJanuary 30, "Gas Illumination," by Dr. William Wallace, F.R.S.E. In the Indian Section-January 17, "Afghanistan," by C. E. D. Black, Col. H. Yule, C. B., R.E., will preside. January 21, "Quest and Early European Settlement of India," by George Birdwood, M.D., C.S.I. February 21, "The Trade of Central Asia, by Trelawney Saunders. March 7, "The Moral and Material Progress of India," by H. Phillips. In the African Section-January 21, Correspondence-The Band-Pattern in Animals-The Sea-Serpent. "Retrospect and Prospect in Egypt," by B. Francis Cobb. February 4, "The Opening of the District to the North of

I. "Progress"-The Alleged Distinction between Man and
Brute.

II. Matter Dead-Roger Bacon and John Dalton.

III. A Contribution to the History of Electric Lighting. By
W. Mattieu Williams, F.C.S., F.R.A.S.

IV. The Problem of Flight-Ballooning in Arctic Exploration.
V. Electric Lighting. By Prof. W. E. Ayrton.
VI. Instinct or Reason?

VII. New Achromatic Microscope.
VIII. Safe Anæsthesia.

IX. On the Transmission of Power by Means of Electricity. By
Profs. Elihu Thomson and Edwin J. Houston.

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THE CHEMICAL NEWS.

VOL. XXXIX. No. 1002.

ON THE

TRANSMISSION OF POWER BY MEANS OF
ELECTRICITY.

By Profs. ELIHU THOMSON and EDWIN J. HOUSTON.

THE statements recently made as to the size and cost of the cable that would be needed to convey the power of Niagara Falls to a distance of several hundred miles by electricity, have induced the authors to write the present paper, in the hope that it may throw light upon this interesting subject.

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Here it will be seen that the introduction of the two additional machines, A' B', has permitted the length of the cable c to be doubled, without increasing the strength of the current which flows, and yet allowing the expenditure of double the power at A A', and a double recovery at B B' of power, or, in other words, a double transmission of power without increase of current. Increase, now, the number of machines at A to say one thousand, and of those at B in like proportion, and the distance between them, or the length of the cable, one thousand, or in the case we have supposed, make it one thousand miles, its diameter remaining the same. Then, although the same current will flow, yet we have a thousand times the expenditure of power at one end of the cable, and a thousandAnd the same would be true for any other proportion. Since the electromotive force is increased in proportion to the increase of power transmission, the insulation of the cable and machines would require to be proportionally increased.

As an example of some of the statements alluded to, we may cite the following, viz.: That made by a certain electrician, who asserts that the thickness of the cable required to convey the current that could be produced by the power of Niagara, would require more copper than exists in the enormous deposits in the region of Lakefold recovery at the other end, without increase of current. Superior. Another statement estimates the cost of the cable at about 60 dols. per lineal foot.

As a matter of fact, however, the thickness of the cable required to convey such power is of no particular moment. Indeed, it is possible, should it be deemed desirable, to

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FIG. 2.

As an example it may be mentioned that a dynamoelectric machine used for the purpose of A in the figure, may have a resistance of say 40 ohms, and produce an electromotive force of say 400 volts. Such a machine might require from three to five horse-power when used in connection with a suitable motor B, for recovery of the power transmitted.

If the resistance of the motor B be, say, 60 ohms, and the cable transmitting the currents a distance of one mile be one ohm, then the current

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2 Miles
C

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Y

Fig. 1, is producing current by the expenditure of power; the other machine, B, used as an electrical motor, is producing power by the current transmitted to it from A by the cable C. The other terminals, x and y, are either put to earth or connected by a separate conductor.

If our

which has manifestly the same value as before. supposition of the power used to drive one machine be correct, then from three to five thousand horse-power would be expended in driving the machines, and possibly about 50 per cent of this amount recovered. Then we Let us suppose that the electromotive force of the have from 1500 to 2000 horse-power conveyed a distance current which flows is unity. Since, by the revolution of of 1000 miles. What diameter of copper cable will be B, a counter-electromotive force is produced to that of A, required for such transmission? Since this cable is supthe electromotive force of the current that flows is mani-posed to have the resistance of one ohm to the mile, calfestly the difference of the two. Let the resistance of A and B together be equal to unity, and that of the mile of

culation would place the requisite thickness at about inch. If, however, the distance be only 500 miles, then

56

Effect of Heat on the Di-iodide of Mercury.

For the consumption of 1,000,000 horse-power a cable of about inches in diameter would suffice under the same conditions. However, by producing a much higher electromotive force, the section of the cable could be proportionally reduced, until the theoretical estimates, which we have given in the first part of this paper, might be fulfilled. The enormous electromotive force required in the above calculation would, however, necessitate such perfect insulation of the cable, that the practical limits might soon be reached. The amount of power required to be conveyed in any one direction would, of course, be dependent upon the uses that could be found for it; and it is hardly conceivable that any one locality could advantageously use the enormous supposed power we have referred to.

CHEMICAL
Feburary 7, 1879.

the resistance per mile may be doubled, or the section of | truncation of the edges until they disappeared, while the cable be decreased one-half, or its diameter will be square-based octahedrons were produced in their place. The iodide is clearly capable of existing in two crystalless than the inch. line forms belonging to different systems, and of passing from one form to the other, either by diminution of temperature or by simple mechanical means. Such a substance would seem to be likely to possess peculiarities in its modes of expansion under the influence of heat. In order to test this the iodide was submitted to the same experimental treatment as that employed in the case of the iodide of silver, and previously described in detail. Homogeneous rods of the iodide of mercury were heated in paraffine in the expansion apparatus described and figured in the previous paper, and the extent of expansion due to a given range of temperature was noted. The apparatus was standardised by means of a rod of fine homogeneous silver. The same micrometer, reading to 80th of an inch, was employed, and the mode of conducting the experiments was precisely the same as in the case of the iodide of silver. Two slight changes were made in the apparatus, however:-the one consisted in the substitution of a massive stone base for the wooden one hitherto used; and the other the replacement of the glass rods moving in stuffing boxes by curved equal-armed levers moving over the rim of the trough, by which means the leakage of hot paraffine at the stuffing boxes was prevented.

Stripped of its theoretical cousiderations the important fact still remains, that with a cable of very limited size, an enormous quantity of power may be transferred to considerable distances. The burning of coal in the mines, and the conveyance of the power generated by the flow of rivers, may therefore be regarded as practicable, always, however, remembering that a loss of about 50 per cent will be almost unavoidable.

It may be mentioned that Dr. C. W. Siemens and Sir William Thomson have recently made statements that are in general accordance with the views here expressed. |

Bars of the iodide of mercury were cast in clean glass tubes, and here at the outset the experimental difficulties commenced. For not only was it difficult to obtain a homogeneous rod, on account of the volatilisation of the iodide at a temperature slightly exceeding its melting

ON THE EFFECT OF HEAT ON THE DI-IODIDE point, but the rod when cold was found to be so brittle that it usually broke in the attempt to remove the glass Eventually good rods were envelope from the outside.

OF MERCURY, HgI2.*

By G. F. RODWELL, Science Master, and H. M. ELDER, a Pupil procured by slowly melting the iodide in thin glass tubes in Marlborough College.

and annealing in hot paraffine. When the whole was cold
the glass was cut on the outside, and carefully broken off
the ends of the rod, which were sawed plane by a fine
steel saw, and then furnished with metal caps, and the
rod was placed between the levers of the expansion
or twice in
apparatus. After heating the bar once
paraffine to a temperature approaching its melting-point
longitudinal rifts appeared in the glass envelope, which
was then easily removed, leaving a clean homogeneous
rod of the iodide.

In continuation of the experiments on the effects of heat on the chloride, bromide, and iodide of silver, which one of us has previously had the honour of communicating to the Society, it was thought to be advisable to search in some of the other metallic iodides for molecular anomalies similar to those presented by the iodide of silver. Among these no substance appeared more likely to On heating a mass of the crimson amorphous iodide, possess such anomalies than the di-iodide of mercury. This substance, as is well known, is dimorphous. In the it turns yellow at 126° C., and just before the meltingamorphous condition it presents the appearance of a bril-point is attained the yellow changes to a deep red-brown. liant scarlet powder, which, if heated, fuses at 200° C., The liquid resulting from the fusion has the appearance of liquid iodide of silver, that is to say, it has the exac and volatilises just above the fusing point to a vapour more colour of bromine. The liquid when cooled solidifies to than twice as dense as that of mercury. The vapour cona red-brown solid, which speedily becomes yellow, and at denses to rhombic prismatic crystals, which frequently 126° C. it changes to the crimson octahedral variety. become scarlet while cooling, but which, if they still reDistinct cracking sounds, due to inter-molecular movemain yellow when cold, instantly become scarlet if rubbed or otherwise mechanically agitated. According to Waring- ments, were heard during the continuance of the change. ton, this change is due to the transformation of the Heat is absorbed when the red iodide changes to yellow, and is given out when the yellow iodide changes to the rhombic prisms into acute square-based octahedrons with red. truncated summits. If the yellow prismatic crystals are A bar of the iodide was placed in the expansion appaplaced under the microscope, and are then touched, the ratus, melted paraffine was forced upon it, and when the change to the red variety may be observed to go on through the mass of contiguous crystals, accompanied by index had become quite steady, a gentle heat was applied a slight movement, but the external form of the crystals to the paraffine. The index showed a regular and slow remains unchanged, consequently pseudomorphous crys- expansion until a temperature of 126° C. was reached, tals are produced; and the larger rhombic prisms have when the bar began to change from the octahedral to the been resolved into a mass of minute octahedrons. Frank-prismatic condition, and without further rise of temperainheim asserts that by the application of a very gentle ture rapid expansion took place. The temperature was heat both the red and the yellow crystals may be sub-kept constant until the change was complete, and was limed together, and he believes that the vapour of the yellow crystal passes off at a lower temperature than that of the red. Warington found that the precipitate produced by iodide of potassium in chloride of mercury appeared under the microscope to be composed of rhom bic lamina, which gradually altered their form by the

*Paper read at the Royal Society.

+ Proc. Royal Society, vol. xxv., p. 230.

then slowly raised. A regular expansion now took place under a higher coefficient than before the molecular change, and this continued until the melting-point was attained. The results were concordant.

The expansion in passing from the solid to the liquid condition was determined by weighing mercury in a tube, and afterwards filling it to the same height with fused iodide. The specific gravity of each substance being

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