CHEMICAL NEWS, Extraction of Gold, Silver, and Other Metals from Pyrites. January 3, 1879. 7 contained in the boiled and filtered water, because | waggon. The roaster is built as a muffle, with a sole of calcium sulphate is practically insoluble at a pres- brick or cast-iron plates laid at a slight incline, to facilisure of one atmosphere of steam. The calcic oxide tate the transference of the charges. At the lower end is determined in 350 c.c. of the boiled and filtered there is a depression of about 6 inches, forming a recess, water, calculated into dry sulphate, and added which extends half way over the reverberatory furnace, and on to solids deposited on boiling. The difference has an opening which can be closed with a slide, through between the number so obtained and the total solids which the contents of the recess may be at once transgives solids retaining solubility on boiling under ferred to the furnace. At the end of the roaster is an pressure, which solids are only of account in as far arsenic flue if required. Farther on is the combination as they augment the boiling-point of the residual chamber, built of sheet-lead, supported by an external water. It will of course be obvious that if framing of wood; the sole is of sheet-lead, supported on a water contains free acids, except carbonic, that iron plates over the flue. The sole is divided into eight latter part of the process will be omitted. stages, each of which is an inch higher than the one nearer the roaster. Beyond the combination chamber is a condensing tower, which may be built of brick, laid in a putty of clay and coal-tar, or, better, sheet-lead, supported by an external framing of wood. The condenser is filled with coke or pebbles, supported on iron bars covered with lead, allowing a free space for the entry of the gases evolved in the roaster. Surmounting the coke is a perforated sheet of lead, with suitable openings for the escape of the residual gases, which may be conducted by a pipe to a chimney. On the perforated lead plate water is delivered at intervals by a self-acting tumbler, kept supplied by a cistern. The water escaping through the holes in the lead plate is uniformly distributed over the coke, and trickles downwards, escaping over the sole of the combination chamber, flowing over each stage in succession, and from the lowest to a wooden cooler, whence it is again pumped to the cistern. I have always viewed the boiling of a water in a thin glass flask as a very excellent method of judging of its scale-forming qualities, and it is quite remarkable to note various peculiarities of deposits so obtained. In reporting an analysis of boiler water made by this method I adopt the following tabulation : Solids deposited by boil ing under pressure Solids remaining in solution on boiling under pressure Grains per gal. Pounds per 100 galls. Then follow remarks as to the analyst's opinion of the water generally. I need hardly say that it is the bounden duty of every one who attempts the analysis of boiler water to make himself well acquainted with the construction and manner of working the different makes of boilers in ordinary use, and also to study well the reactions of the various salts natural waters contain when subject to heat and pressure combined. When one views the evidence produced before coroners' juries dealing with cases of death from boiler explosions, it is often very painfully apparent that there is a great deal yet to be done by chemists in the tracing of effect to cause, the information afforded being often of the most meagre quality, and a field of inquiry embracing the salvation of life and property is surely one in which honour is not wanting. Laboratory and Assay Office, Darlington, December 19, 1878. ON THE The roaster soie being heated to a dull red heat, 2 cwts. of the dressed pyrites, or ground regulus, is mixed with from 10 to 15 per cent of previously roasted ore, and charged into the upper end of the roaster, so that it occupies about 2 feet of the length, and spreads across the sole, which it should cover to the depth of one and a half inches. The ore soon becomes ignited, evolving sulphurous, sulphuric, and arsenious oxides. The last is condensed in the arsenic flue, and the two former pass through the combination chamber to the condensing tower, and are there absorbed by the descending water. In an hour's time the charge is moved 2 feet to the left, and a second charge of the mixture is placed in the space METHOD OF EXTRACTING GOLD, SILVER, AND cleared. At the end of another hour the first charge is OTHER METALS FROM PYRITES.* By W. A. DIXON, F.C.S., Cor. Mem. Nat. Hist. Soc. Glasgow. (Concluded from p. 303). THE method of treatment of the concentrated ore, or regulus, is the same whether the sulphides are rich in the precious metals or not, but requires variation according to-First, the presence or absence of copper; second, the proportion of copper; and, third, the presence or absence of lead. from copper. To begin with the simplest case, viz., with pyrites free The apparatus required consists of-1, a roaster; 2, a reverberatory furnace; 3, an arsenic flue, (if the pyrites are arsenical); 4, a leaden combination chamber; 5, a leaden condensing tower; 6, a series of lixiviating tanks and coolers. It is best to construct the furnace, roaster, arsenic flue, converting chamber, and tower in one line, so that the waste heat from the reverberatory furnace heats the sole of the roaster and converting chamber. The reverberatory furnace is constructed in the usual manner, but the sole is made simply of brick, and flat, with an opening in the centre or side, through which the charge may be raked out into an iron hopper * Read before the Royal Society of N.S.W. August 1, 1877. moved 2 feet to the left, the second to the space cleared, and a third is introduced, and so on, until at the end of twenty-four hours the sole of the roaster is covered. The upper part of the roaster should be at a very dull red heat, whilst the lower should be sufficiently hot to decompose any sulphate of iron formed. charcoal-dust, or other carbonaceous matter is now spread, On the sole of the recess from 35 to 40 lbs. of coal-dust, and the calcined residue from the first charge is turned downwards, and a fresh charge of mixture introduced. In over on top of it, each charge in the roaster is moved another hour a similar quantity of carbon is spread on top of the charge in the recess, and the second charge is turned over on top, and so on until eight successive charges of roasted residue and carbon are in the recess. The contents of the recess are then transferred to the reverberatory furnace through the opening; the whole is well stirred up, and spread over the sole. The furnace is closed, and kept at a moderate red-heat for eight hours, the furnace being kept full of a smoky flame to assist reduction. The oxides are thus reduced to the metallic At the end state, and the heat should be kept so low as to prevent the 8 Extraction of Gold, Silver, and Other Metals from Pyrites. (CHEMICAL NEWS, furnace is again charged from the recess, which has meanwhile been filled. When the hopper is cool enough to be handled, the contents are rapidly transferred to a vessel containing water, best by placing the waggon over the vessel and withdrawing a slide in its bottom, so as at once to thoroughly wet and cool the contents. One-eighth part, or thereabouts, of the cooled metal is now placed in the upper stage of the combination chamber, over which water from the condenser, charged with sul phurous and sulphuric acids, is flowing. In one hour the charge is moved to the second stage, and a second charge is introduced, and so on, until in eight hours the chamber is filled, and that furnace charge exhausted. The metal is rapidly acted on by the acids, and converted into sulphate, sulphite, and hyposulphite of iron; but by the combined action of the air and water, assisted by the heat from the flue, the first largely predominates. The charge on the lowest stage is now removed, and may be at once lixiviated with water; but it is best to keep it for a few days in a moist state, to finish the conversion into sulphate. It is then lixiviated with water, which removes sulphate of iron (also zinc, nickel, and cobalt if present), and leaves a residue containing the gold and silver, mixed with quartz, excess of carbon, and free sulphur. The carbon and sulphur are then burned off, and the gold and silver separated from the quartz by washing, amalgamating, or otherwise. If the extraction of the sulphate of iron is effected with boiling water, and the liquor run into coolers, that salt may be obtained in a marketable condition; or, the crystals being calcined at a dull-red heat, yield a fine red oxide of iron suitable for painting, and sulphuric acid, which may be condensed. If the ores contain copper in small proportion only, the roasting, reduction, and solution of the iron are conducted precisely as above described, using, however, as little carbon as possible for the reduction, so as to obtain the residue nearly free therefrom. The copper is then found in the residue principally as sulphide. This residue is roasted at a dull red heat, and the copper is extracted by treatment with condenser liquor and crystallisation, as described below, the gold and silver being obtained from the residue as before. Ores or sulphides containing much copper are roasted at a dull red heat, the mixing with roasted ore, roasting, and condensation of the gases being conducted as before. The well-roasted ore is withdrawn from the furnace and cooled. The cooled residue is then shaken into a lixiviating tank partly filled with a solution of sulphate of copper, containing sulphuric acid and sulphurous acid, obtained as below described; the mixture is allowed to digest, and treated with successive portions of the solid solution until the escaping liquer contains free sulphuric acid. The lixiviation is then carried on with a cold saturated solution of sulphate of copper from the coolers, which is made boiling hot in a leaden or copper boiler, until the specific gravity of the entering and escaping solutions is the same. The whole of the copper liquors are run into wooden coolers, where crystals of the sulphates of copper and iron are deposited. When the lixiviation has been carried as far as possible with the copper solution, it is drawn from the tank until it stands only an inch or so above the solid contents, and 12 inches of water are carefully floated on top, and the drawing off the copper solution continued from below until the water is only an inch above the solid contents, when a second wash is run on, and in the same manner a third if necessary. The copper liquors are run to the coolers as long as they mark above 20° of Twaddel, below that strength they are run to a separate tank to be used for the first wash of another lot. If the ore contains silver, a little is found in solution in the copper liquor, and is separated therefrom by filtering it through a bed or beds of cement copper, or, better, of precipitated sulphide of copper, before running the liquor to the coolers. The silver is recovered from time to time January 3, 1879. by roasting the precipitate, extracting the copper by condenser liquor, and melting the residual silver. The residue in the lixiviating tanks is drained, dried, mixed with one-fourth of its weight of carbon, reduced, and otherwise treated as above described, to obtain the gold and remaining silver. The crystals of sulphates of copper and iron in the coolers are removed from time to time, drained and dried. One ton of the dried crystals is charged into the muffle furnace, and there exposed to a fully cherry-red heat, so as to convert the whole of the sulphates into oxides. The sulphurous and sulphuric acids evolved are conveyed to the condensing tower, which is supplied with sulphate of copper solution from the coolers, slightly diluted with the weaker wash liquor by which the acids are condensed, When vapours are and used for extracting roasted ore. no longer evolved the calcined residue is removed from the muffle. A similar charge of dried sulphate is heated in the muffle furnace to a dull red, so as to convert the sulphate of iron into oxide, and when fumes are no longer evolved the charge is raked out, mixed with 2 cwts. of coal or charcoal dust, and charged into the reverberatory furnace, where it is melted, when sulphurous and other gases are evolved, causing the mass to boil. When boil. ing ceases the oxides are added to the charge, and the melting heat continued until the whole is in a tranquil fusion, when the slags are raked off and the rough copper run into moulds. If the ore contains lead it is found in the residue con taining the gold and silver; and if present in sufficient quantity the residue may be smelted, and the gold and silver recovered by cupellation. If not present in sufficient quantity to smelt, but still so is roasted, treated with a little condenser liquor, washed, much as to interfere with the amalgamation, the residue and the lead extracted with solution of caustic soda, when the gold and silver may be amalgamated. The solution of lead in caustic soda is mixed with sawdust or carbon, evaporated to dryness, heated strongly, and the carbonate of soda dissolved out with water, and again rendered caustic by lime, when the lead remains as an insoluble residue mixed with carbon. The advantages of this mode of treatment are that the sulphides are entirely got rid of, whilst if through inattention in the roasting some sulphides remain, only the small proportion that has escaped requires to be re-roasted, instead of the whole mass of ore as is usually the case. In the extraction of copper from the sulphides the whole of the copper may be obtained in the form of crystals, from which the copper may be recovered without evaporation of liquors; and in the whole of the operations, with the exception of smelting for copper, the temperatures are so low that the cheapest materials may be used for the construction of furnaces. The temperature being low, the loss of silver by volatilisation is reduced to a minimum, whilst there is absolutely no loss of gold, except through the careless spilling of the material. Lastly, as neither salt, iron, or other material is consumed in the process, a large source of expense in all previous wet methods of treatment is avoided; and the process is adapted for use wherever the ores are found. PROCEEDINGS OF SOCIETIES. MANCHESTER LITERARY AND PHILOSOPHICAL SOCIETY. Ordinary Meeting, November 26, 1878. J. P. JOULE, D.C.L., LL.D., F.R.S., &c., President, in the Chair. "On some Improved Methods of Producing and Regu lating Electric Light," Part II., by HENRY WILDE. duced. When the circuit is interrupted the armature is released; the upper ends of the carbons come into con tact, and the light is produced as before. When several pairs of carbons are placed in the same circuit they are, by this arrangement, lighted simultaneously. In a former communication to the Society I directed attention to the fact that when the electric light is produced from the ends of two carbon pencils placed parallel to each other, if the strength of the electric current, the thickness of the carbons, and the distance between them are rightly proportioned, the carbons will burn steadily downwards until they are wholly consumed, without any insulating material between them. To initiate the light by this method it is necessary to complete the electric CHEMICAL NOTICES FROM FOREIGN circuit between the carbons by means of some conducting substance, which volatilises on the passage of the current, and establishes the electric arc between the points. When a number of such lights are produced simultaneously from the same source of electricity, any interruption in the continuity of the current extinguishes all the lights in the same circuit, and each pair of carbons re SOURCES. NOTE. All degrees of temperature are Centigrade, unless otherwise expressed. quires to be re-primed before the lights can again be Comptes Rendus Hebdomadaires des Séances, l'Académie de established. This defect, as will be obvious, would cause great inconvenience when the lights are not easily accessible, or are at considerable distances apart. In the course of my experiments it was observed that when the electric circuit was completed at the bottom of a pair of carbons close to the holders, the arc immediately ascended to the points, where it remained so long as the current was transmitted. My first impression of this peculiar action of the arc was, that it was due to the ascending current of hot air by which it was surrounded. This, however, was found not to be the cause, as the arc travelled towards the points in whatever position the carbons were placed, whether horizontally or vertically in an inverted position. Moreover, when a pair of carbons were held in the middle of the holders, the arc travelled upwards or downwards towards the points, according as the circuit was established above or below the holders. The action was in fact recognised to be the same as that which determines the propagation of an electric current through two rectilinear and parallel conductors submerged in contact with the terrestrial bed, which was described by me in the Philosophical Magazine, August, 1868. Το des Sciences. No. 24, December 9, 1878. Contains.-MM. Ste.-Claire Deville, Des Cloizeau, and Automatic Current-Regulator.-M. Hospitalier.—By means of the author's apparatus the intensity of a current may be maintained between two limits fixed beforehand, and which may be as near together as is desired. Note on a Remarkable Specimen of Iron Silicide. J. Lawrence Smith.-The specimen has the appearance of an ingot from the blast-furnace and has a brilliant surface. It resists nearly all reagents except hydrofluoric acid and caustic alkalies at a red heat. It contains 15 per cent of silicium, whilst the alloy of iron and manganese richest in silicium has only 10 per cent. Its origin is unknown. In all the arrangements in general use for regulating the electric light, the carbon pencils are placed in the same straight line, and end to end. When the light is required, the ends are brought into momentary contact, and are then separated a short distance to enable the arc to form between them. The peculiar behaviour of the electric arc when the carbons are placed parallel to each other suggested to me the means of lighting the carbons automatically, notwithstanding the fact that they could only be made to approach each other by a motion laterally, and to come into contact at their adjacent sides. accomplish this object one of the carbon holders is articulated or hinged to a small base plate of cast-iron, which is so constructed as to become an electro-magnet when coiled with a few turns of insulated wire. The carbon holder is made in the form of a right-angled lever, to the short horizontal limb of which is fixed an armature Formation of Hexamethyl-benzin by the Decomplaced over the poles of the electro-magnet. When the movable and fixed carbon holders are brought into juxtaposition of Aceton.-W. H. Greene.-The author has position, and the carbons inserted in them, the upper parts obtained this product in quantity by the action of aceton of the two carbons are always in contact when no current upon melted chloride of zinc at a high temperature. is transmitted through them. Normal Ethyl-oxy-butyric Acid and its Derivatives. M. Duvillier.-An examination of the ethyl-oxybutyrate of methyl and of ethyl-oxy-butyramide. The contact between the carbons is maintained by means of an antagonistic spring inserted in a recess in one of the poles of the electro-magnet, and reacting on the under side of the armature. One extremity of the coil of the electro-magnet is in metallic connection with the base of the carbon holder, while the other extremity of the coil is in connection with the terminal screw at the base of the instrument, from which it is insulated. The coils of the electro-magnet are thus placed in the same circuit as the carbon pencils. When the alternating current from an electro-magnetic induction machine is transmitted through the carbons, the electro-magnet attracts the armature and separates the upper ends of the carbons, which brings them into their normal position, and the light is immediately pro A New Acid Derived from Camphor.-A. Haller. -The author has obtained a homologue of camphoric acid, which he proposes to name hydroxy-campho-carbonic acid, C11H1804. It decomposes the alkaline and alkaline-earthy carbonates, forming salts with their bases. The author has analysed the salts of lead, copper, and zinc. Presence of Ytterbium in the Sipylite of Amherst (Virginia).-Marc Delafontaine.-The author has isolated from this mineral a base whose characters agree closely with those of M. Marignac's ytterbia. Existence of Baryta and Strontia in all the Rocks forming Primordial Districts.-M. Dieulafait.-The author finds that these earths are easily recognised in felspars, in the mica of primitive rocks, in granites coarse or fine, and in syenite. The author considers that these rocks are the original source of baryta and strontia. Danger of the Use of Borax for the Preservation of Food, and Causes why certain Substances Deprive Scammell. {CHEMICAL NEWS, January 3, 1879. Materia Medica.-(Medal) Mr. Newbigin; (Certificates) Mr. Lemmon and Mr. Harrison, equal. Practical Pharmacy and Dispensing. (Medal) Mr. Lemmon; (Certificate) Mr. Lord. Silver Medal of the School, for Session 1877-78.-Mr. John E. Phillips. NOTES AND QUERIES. Meat of its Nutritive Properties.-G. Le Bon.--Meat | bigin. Botany.-(Medal) Mr. Lord; (Certificate) Mr. steeped in a solution of pure borax, or covered with the powdered salt, may be preserved unchanged for a long time, but if taken as food such meat produces intestinal derangements, which necessitates its disuse. Borax, taken in small successive doses, is a poisonous agent, the use of which in the preservation of alimentary substances ought to be strictly prohibited. M. Peligot has already pointed out the poisonous action of borax upon plants. Several compagnies in America, who had begun to use this salt for the preservation of meat, have been obliged to give it up. The author further shows the necessity of avoiding saline substances altogether for the preservation of food, an object which he considers attainable solely by the use of cold. MISCELLANEOUS. As halte Pitch.-Will any of your correspondents kindly give me any information of the best method of making asphalte pitch, and the way to make it into "blocks" ready for use?-J. R. Peroxide of Hydrogen.-Will any of your readers inform me how I can obtain information how to make peroxide of hydrogen of ten volumes strength? I want it for commercial purposes.-THOMAS WARDLE. Distillation of Tar.-(Reply to R. J.)-The best work on the distillation of tar, &c., is by Dr. George Lunge, published by Vieweg and Sohn, Brunswick.-DESTRUCTIVE DISTILLATOR. MEETINGS FOR THE WEEK. MONDAY, Jan. 6th.-Medical, 8. "On Pilo. lite, an unrecognised species," by Prof. M. F. Heddle. "On so-called Green Garnets from the Urals," by Prof. A. H. Church. "On the Magnetism of Rocks and Minerals," by J. B. Hannay, F.C.S. "On the Celestine and Baryto-celestine of Clifton," by J. N. Collie; communicated by W. W. Stoddart. On some Silicates of Copper," by W. Semmons. "Contributions towards a History of British Meteorites, by Townshend M. Hall, F.G.S. "Notes on some Crystals of Iron," by Amos "Additional Note on Pen Beardsley, F.G.S. withite," by J. H. Collins, F.G.S. Anthropological, 8. WEDNESDAY, 8th.-Geological, 8. Microscopical, 8. Quekett, 8. CULLEY'S PRACTICAL TELEGRAPHY. In One Volume, 8vo., with 132 Woodcuts and 18 Lithographic Plates of Machinery and Apparatus, Price 16s. A HANDBOOK OF PRACTICAL TELE GRAPHY. By R. S. CULLEY, Member Inst. C.E. (Adopted University of London.-The following are lists of the candidates who have passed the recent examinations: -Second B.A. and Second B.Sc. Examinations.-Examinations for Honours (B.A. and B.Sc. conjointly).-Mathematics. First Class: J. Larmor, B.Sc. (Scholarship), St. John's College, Cambridge; W. H. Gunston,* B.A., St. John's, Cambridge. Third Class: J. A. Owen, B.Sc., private study. Logic and Psychology. First Class: W. K. Griffin, B.Sc., University College and private study. Second Class: S. W. Bowser, B.A., University and Regent's Park College; J. Enright, B.Sc.. St. Mary's Hospital and King's College; J. Browne, B.A., Stonyhurst College. Third Class: I. Abrahams, B.A., Jews' and University Colleges; R. Gill, B.Sc., St. Bartholomew's Hospital; G. A. Stebbing, B.A., Catholic University FRIDAY, 10th.-Astronomical 8. College, Kensington; G. E. Ford, B.A., University College; J. W. Greig, B.A., University College; J. J. Beuzemaker, B.A., private study; R. A. Freeman, B.A., private study. Classics (B.A only). First Class: F. C. Montague (Scholarship), Balliol College, Oxford; A. W. Lockyer, private study. Second Class: E. Etherington, Stonyhurst College; G. F. Colborne, private study and tuition; H. H. C. Thurston. Stonyhurst College; T. Slater, Stonyhurst College. Third Class: J. Browne, Stonyhurst College; C. G. Higginson, Owens College; C. T. Galton, Stonyhurst College. French. First Class: J. W. Greig (Prize) University College; O. E. Boding-QUARTERLY JOURNAL OF SCIENCE. ton, Giggleswick School and private tuition; F. J. Morrish, Cheshunt College and private study. Second Class: F. P. Hartley, private study; C. G. Higginson, Owens College. Third Class: E. A. Durham, private study; G. Board, private study. German. Second Class: C. T. Galton, Stonyhurst; J. T. Christie, King's College, London, and Exeter, Oxford. Chemistry (B.Sc. only). R. Gill, St. Bartholemew's Hospital; C. F. Cross, King's and Owens Colleges. Experimental Physics. Second Glass: L. H. Edmunds, University College. Third Class: M. F. O'Reilly, St. Joseph's College, Clapham; G. W. von Tunzelmann, University College. Physical Geography and Geology. Second Class: T. Gough, private study and Royal College of Chemistry. Third Class: G. H. Bailey, University College and private study; P. N. Bose, University College. Botany. First Class: T. Gough, private study and Royal College of Chemistry. Third Class: P. N. Bose, University College. Zoology. Second Class: S. H. C. Martin, University College. South London School of Pharmacy.-The sixth Annual Dinner took place at the Horns Assembly Rooms on Friday, the 20th ult. There were about 130 old and new students present, together with a large number of gentlemen interested in the progress of the School. Dr. Julius Pollock presented the prizes to the following successful students :- -Senior Chemistry.- (Medal) Mr. Pocock; (Certificate) Miss Stammwitz. Junior Chemistry. (Medal) Mr. Harrison; (Certificate) Mr. New * Obtained the number of marks qualifying for the Scholarship. I. THE Edited by WILLIAM CROOKES, F.R.S., &c. Now ready, No. LXI., January, 1879, price 58. On the Thickness of the Antarctic Ice, and its Relations to II. III. Sanitary Science in the United States: Its Present and its IV. V. The Course of Nature. By Prof. Simon Newcomb. THE JOURNAL OF SCIENCE. The JOURNAL OF SCIENCE will in future be issued MONTHLY instead of QUARTERLY, and will consist of 45 pp., the form and general appearance remaining the same. The first of the Monthly issue will appear on Price ONE SHILLING and SIXPENCE. the spectra of the brighter stars before this point could THE CHEMICAL NEWS. be determined. VOL. XXXIX. No. 998. DISCUSSION OF THE WORKING HYPOTHESIS By J. NORMAN LOCKYER, F.R.S. (Concluded from p. 5.) II. I also remarked that this result enabled us to fix with very considerable accuracy the electric dissociating conditions which are equivalent to that degree of dissociation at present at work in the sun. In Fig. 3 I have collected several spectra copied from photographs in order that the line of argument may be grasped. First we see what happens to the non-dissociated and the dissociated chloride. Next we have the lines with a weak voltaic arc, the single line to the right (W. L. 4226'3) is much thicker than the two lines (W. L. 3933 and 3968) to the left, and reverses itself. We have next calcium exposed to a current of higher tension. It will be seen that here the three lines are almost equally thick, and all reverse themselves. Now it will be recollected, that in the case of known Application of the above Views to Calcium, Iron, Lithium, compounds the band structure of the true compounds is and Hydrogen. Calcium. reduced as dissociation works its way, and the spectrum of each constituent element makes its appearance. If in It was in a communication to the Royal Society made 3 we take the wide line as representing the banded specnow some time ago (Proc., vol. xxii., p. 380, 1874), that I trum of the compound, and the thinner ones as representfirst referred to the possibility that the well-known line- ing the longest elemental lines making their appearance spectra of the elementary bodies might not result from as the result of partial dissociation, we have, by hypothethe vibration of similar molecules. I was led to make the sis, an element behaving like a compound. FIG. 3.-THE BLUE END OF THE SPECTRUM OF CALCIUM UNDER DIFFERENT CONDITIONS. 1. Calcium is combined with chlorine (CaCl). When the temperature is low, the compound molecule vibrates as a whole, the spectrum is at the red end, and no lines of calcium are seen. 2. The line of the metal seen when the compoun molecule is dissociated to a slight extent with an induced current. 3. The spectrum of metallic calcium in the electric arc with a small number of cells. 4. The same when the number of cells is increased. 5. The spectrum when a coil and small jar are employed. 6. The spectrum when a large coil and large jar are used. 7. The absorption of the calcium vapour in the sun. remark in consequence of the differences to which I have already drawn attention in the spectra of certain elements as observed in the spectrum of the sun and in those obtained with the ordinary instrumental appliances. Later (Proc. Roy. Soc., No. 168, 1876) I produced evidence that the molecular grouping of calcium which, with a small induction-coil and small jar, gives a spectrum with its chief line in the blue, is nearly broken up in the sun, and quite broken up in the discharge from a large coil and jar, into another or others with lines in the violet. I said "another," or "others," because I was not then able to determine whether the last-named lines proceeded from the same or different molecules; and I added that it was possible we might have to wait for photographs of * Paper read at the Royal Society, December 12, 1878. If the hypothesis be true, we ought to be able not only to obtain, with lower temperatures, a still greater preponderance of the single line, as we do; but with higher temperatures, a still greater preponderance of the double ones, as we do. I tested this in the following manner :-Employing photography, because the visibility of the more refrangible lines is small, and because a permanent record of an experiment, free as it must be from all bias, is a very precious thing. Induced currents of electricity were employed in order that all the photographic results might be comparable. To represent the lowest temperature I used a small induction coil and a Leyden jar only just large enough to secure the requisite amount of photographic effect. To represent the highest, I used the largest coil and jar at my disposal. The spark was then taken between two alu |