cursed them by candle, by bell, and by book; but, as in the "Jackdaw of Rheims " "What gave rise to no little surprise, Nobody seemed one penny the worse." (The curse may be read in full in the "Life and Adventures of Tristram Shandy"), for very soon the works succeeded so well that several more were established. These works at Gisborough are, I believe, still carried on. According to Ure, the manufacture of this salt was begun at Harlet, in Scotland, by Nicholson and Lightbody in 1766; abandoned, and resumed by Macintosh and Wilson in 1797. The old method of manufacture, such as is carried on at Hurlet and Whitby, is to roast the shale, lixiviate with water, evaporate the lixivium, and then precipitate the alum by alkaline salt, then wash the alum flour, then crystallise. First, as to the preparation of the alum shale. Some of these shales, when piled in the open air, get spontaneously hot from the oxidation of the iron pyrites into sulphate of iron; and as the process goes on the sulphuric acid is transferred to the alumina with the formation of sulphate of alumina. These heaps soon fall into a porous mass; when they can be readily lixiviated. Those shales which contain too little carbonaceous matter to carry on the combustion must have this added as the piling goes on. At Whitby they use brushwood, and at Harlet small coal for the lower bed, and then the piling of the shale commences. When they have got to the height of three or four feet the mass is kindled, and more shale is piled up. At Whitby this piling process goes on till the heap is 90 or 100 feet high. The horizontal area is also augumented till it forms a bed nearly 200 feet square, having, therefore, about 100,000 yards of solid measurement. At Harlet the height of the heap is only a few feet while the horizontal area is expanded. At Whitby 130 tons of calcined schist produce one ton of alum (Ure). Great care is required in the calcining of these heaps, so as not to lose too much sulphur and sulphuric acid. Rather a slow, continual fire is the best; for if the heat rises too high then a kind of slag may be formed. When this process is over the heap is very much diminished in size. The second process is the lixiviation. The calcined schist is put into cisterns, having the large pieces at the bottom. Water is run over it, and allowed to rest some time; it is then drawn off into another cistern, fresh water is put upon the schist-which, being weak, is run into a separate tank-and sometimes the ore is treated with a third addition of water and the exhausted ore is removed from the cisterns and piled in a heap, and sometimes calcined again, for it even now contains a large percentage of alumina-as much as 12 per cent. goes The third process is the evaporation of these washings, and this is done by what is called a surface fire, because there is so much sediment deposited. The operation is conducted in a large stone cistern about six feet wide, three feet deep, and forty long, and covered by an arch of stone or brickwork. At one end is the firegrate, at the other the chimney; the cistern is filled, and the flame plays along the surface. As the concentration on more of the lixivium is run in till the whole gets of the proper strength, when it is transferred to the leaden boilers. These lead pans are about eight feet long, nearly five feet wide, and two deep at one end, and a little more than two and a-half at the other; the increase of depth is to facilitate the syphoning off. In these lead pans the liquid is boiled; every morning the pans are emptied into a settling cistern of stone or lead. The fourth process is the precipitation of the alum by adding alkaline salts. The clear liquor is run off into the precipitating cistern, and the potash or ammonia salts are added to it; the alum is precipitated in a granular powder. When it is thoroughly settled and cool, the mother liquor is drawn off into a lower cistern. The fifth operation is the washing of the alum flour, because it has a brown colour, from admixture of iron compounds. This is done by means of very cold water, and after the second washing the alum is pretty pure, and this flour is sometimes sent into the market because it dissolves easily. The sixth and last process is the crystallisation. The washed crystals are dissolved in water at a boiling heat. When the liquid is saturated, it is run into the crystallisation vessels or roaching casks; at the end of eight or ten days the alum is broken up and dried, and is then ready for the market. This process of making alum is certainly very rude, and is also attended by great waste of time and labour. This mode of manufacture will very likely disappear altogether, because of the improved methods Mr. Spence, of Manchester, has brought out. He has, indeed, quite revolutionised the alum trade; but any one reading the article on alum in Dr. Muspratt's Dictionary of Chemistry" would think that the new process was not at all different from the old. Dr. Muspratt gives Mr. Spence's process in the following words: "Spence, who lately sealed a patent for the manufacture of alum, offers the following as his method of calcination:--He forms on the ground a number of air channels, by laying parallel lines of common brick at the distance of four inches apart, and placing others on them crosswise; thus the channel formed is about four inches square. The transverse bricks are placed on loosely, so as to allow the air to pass freely upwards, burning coals are laid on the channels, and a layer of the shale, which is most bituminous, broken into small pieces, and as the combustion proceeds, other layers of the shale fragments, less bituminous than the preceding, are put on continuously, but not in too great a quantity. The thickness of each layer should be regulated by the briskness of the combustion, which should never go beyond a low red heat, but care must be exercised in maintaining the bed at this point, as a higher temperature would be apt to glaze or partially flux the materials, and render the alumina less soluble in acid. An examination of the following figure, exhibiting the heaps or mounds in various stages of progress, will show that a similar method to this is practised at Hurlet." This is a most unfair description of such important alum works as Mr. Spence's are, and I am surprised to find such a statement in such a compendious dictionary as Dr. Muspratt's professes to be; in such a book as the one mentioned, one looks to find all the newest improvements, and not so much about operations practised a century ago. Mr. Spence's process is totally different from the old, as any one reading the following will see:— By the old process the manufacturer would have to wait about twelve months or more before he would have any alum ready for the market; by the new it would only be about one month. Mr. Spence has now become one of the largest manufacturers in the world, producing nearly 150 tons a week. It is to be hoped that in the next edition of the dictionary a better description will be given. (To be continued.) To Thaw out Frozen Pumps.—A pint of salt has been found generally sufficient. Two pints have been found enough to thaw through three feet deep. An hour's time suffices in ordinary cases.-Vermont Phoenix. NEWS Professor W. A. MILLER, M.D., F.R.S., President, AFTER the minutes had been read, Mr. W. Tilden, of the Pharmaceutical Society's Laboratory, was formally admitted a Fellow of the Society; and Mr. James Parkinson, Royal School of Mines, and Mr. Frederic Rowe, Colchester, were balloted for and duly elected as Fellows. The names of Mr. William Marriott, Huddersfield, and Mr. Charles Umney, 40, Aldersgate Street, London, were read for the second time, and several new candidates were proposed, whose names were read as under :-John Hunter, M.A., Queen's College, Belfast; Mr. Theodore Maxwell; Mr. William Jacob Barnes, Starling Lodge, Buckhurst Hill, Essex; Mr. W. E. Bickerdike, Dalton Square, Lancaster; Mr. Richard Fitz' Hugh, Nottingham; Dr. William B. Ritchie, Belfast; and Mr. Alfred Gardiner Brown, Member of the Royal College of Surgeons, Trinity Square, South wark. The list of donations to the Society's library was unusually long, and the President announced that at the next meeting of the Society, before commencing the ordinary business, the members would resolve themselves into a Committee "to consider the best means of disposing of several chemical specimens in the Society's possession." He had great pleasure in calling attention to the admirable arrangements made for the ventilation of the meetingroom, which had been jointly undertaken by Dr. De la Rue and Dr. Matthiessen. [These consisted of a spacious perforated grating near the ceiling, which communicated with an air-shaft, in which a series of gas jets, circular in form, were burning. There were also numerous small apertures on either side of the room for the admission of fresh air, opening beneath the platform upon which the seats are placed. The efficacy of the ventilator was apparent throughout the evening; but at the close of the proceedings Dr. De la Rue fired a small portion of gunpowder to show how rapidly the smoke made its escape. A handsome cornice and spring roller, from which diagrams may be suspended, have been placed in front of the grating, the aperture of which can be regulated at will by a sliding shutter.] Professor A. H. CHURCH was then invited to give an account of his "Chemical Researches on some New Cornish Minerals." The speaker stated that in July last he visited Cornwall and collected some fifty or sixty mineral specimens, which included many interesting varieties of wellknown species. In seven instances he was induced to make complete analytical examinations, and by the results was led to the conclusion that three of the minerals had not previously been described; these were : I. Hydrated phosphate of cerium. II. Hydrated phosphate of calcium and aluminium. III. Hydrated arseniate of copper and lead. With respect to the first of these minerals, Mr. Church said he believed there was no instance on record of cerium having been previously discovered in Great Britain. He was indebted for the specimen to Mr. Richard Talling, of Lostwithiel, and at first it was believed to be a kind of Wavellite, but the precipitate furnished by ammonia in the course of analysis became reddish-brown upon ignition, and gave off chlorine during subsequent solution in hydrochloric acid. These characters seemed to indicate the presence of oxide of cerium, which was confirmed by the slightly pinkish hue of the precipitate thrown down by oxalate of ammonia, by the blowpipe reactions, and, finally, by the formation of very definite crystals of the double sulphate of cerium and potassium. The mineral was found to contain upwards of 50 per cent. of cerous oxide, about 5 per cent. of lime, and 28 of phosphoric acid, with about 15 per cent. of water. Its mineralogical formula would, therefore, be expressed thus: (Ceş Caд), P+4H, which is equivalent, under the new atomic system, to 5Ce"O,Ca′′O,2P2O5 + 8H2O. The colour of the mineral was a pale smoke grey, with a slight inclination to flesh-red, and its general aspect is slightly pearly. The crystals, as defined by Professor W. H. Miller, are doubly refractive and of the oblique prismatic system, and they commonly occur in fan-like aggregations. The hardness and density of the mineral are both expressed approximatively by the figure 3. The small quantity of the sample placed at the author's disposal prevented his making any reliable examination for fluorine, and the quartz matrix added to the difficulty. The mineral most nearly allied to that now described is cryptolite-a phosphate of cerium containing neither calcium nor water. The hydrated phosphate of calcium and aluminium, although classed among the minerals from Cornwall came from the borders of that county, and occurred in a copper lode at Tavistock, South Devon. It is a white, silky, fibrous mineral, somewhat difficultly soluble in acids. Although very different in physical appearance, it seems to be identical with the rounded pebbles found in the diamond sands of Bahia, and described by M. Damour in 1853. Its mineralogical formula is,— Ca2P + Al 3H and corresponding chemical expression (new system),— 3 Ca′′O,P,O,Al1⁄2”O3+3H2O. The third mineral which had been submitted to analysis by Professor Church was a variety of Olivenite or arseniate of copper, but differed from it both in colour and density, and was found to contain as much as 30 per cent. of plumbic oxide. Its specific gravity was 5'35; colour, sap green, and lustre resinous. The specimen contained but a small proportion of phosphoric acid, and proved to be a hydrated arseniate of copper and lead, for which the author proposed the formula, 5 Pb"O.2 Cu"O, As,O,+Cu"H2O2+aq. The author proposed to confer upon this new mineral the name of Bayldonite. The PRESIDENT, in moving a vote of thanks to Professor Church, inquired whether other metals of the cerium group, particularly didymium, had been found in the new mineral phosphate of British origin? Professor CHURCH answered in the affirmative, an examination of an optical character having been made by Mr. C. Greville Williams, who distinctly identified the didymium bands. [Vide CHEMICAL NEWS, p., 183 of this volume.] Professor MASKELYNE said that great credit was due to Mr. Church for the successful manner in which he had worked out the composition from so small a quantity of material. He had himself received two specimens of the cerium mineral from Mr. Talling (who was a most indefatigable collector), and had measured the angles as long since as two years ago; he had likewise identified the phosphoric acid. For the rest, he might almost say that he envied Mr. Church his means of research, for he had applied to the authorities of the British Museum for a chemical laboratory in which to make such analytical examinations as the present, but they were opposed to carrying out his suggestion. He had brought with him the two specimens for comparison with that which had been shown by Professor Church, and he had no doubt they were the same thing. After the publication of the analytical details, he hoped to do a little more with the goniometer, but already he was satisfied of their being square prisms. The mineral monazite was likewise a phosphate of cerium containing thorium and about 2 per cent. of lime, and it would be interesting to know whether this rare earth occurred in the Cornish specimen. The speaker had compared and measured at least twenty mineral specimens which might be included under the group Olivenite, and found many that would repay a chemical examination. He regretted that he had no means of undertaking this. Professor Maskelyne concluded by pronouncing a tribute of praise to Richard Talling, of Lostwithiel, who had done so much for mineralogy by his successful search after new minerals. Professor CHURCH described the steps taken in testing for thoria, and believed it was absent, since the whole of the earth in the Cornish mineral was precipitated by excess of ammonia, which is not the case with thoria. Besides, he obtained 100 parts by adding together the weights of the several constituents. He would be happy to lend his specimen to Professor Maskelyne for determination of its crystallographic characters. A paper "On Caprylic and Enanthylic Alcohols," by Mr. Ernest T. Chapman, was read by the Secretary. The author referred to the uncertainty respecting the exact nature of the products obtained on distilling castor-oil soap with an excess of alkali, and proposed to address himself to the determination of the composition of a liquid boiling at about 178° C., in regard to the homogeneity of which there was a doubt. As the general result of the author's investigation, it may be stated that the composition of the distillate is by no means constant, and that both caprylic and oenanthylic alcohols in varying proportions are formed under these circumstances. Several analyses gave numbers closely according with CHO, and the production of caprylic alcohol was further proved by the formation from it of tri-caprylamine. Mr. Chapman incidentally prepared caprylic ether by the action of bromide of capryl upon potasso-caprylic alcohol. Dr. ODLING remarked that castor-oil itself was not likely to be a definite substance, and might yield products of one or other series, or a mixture, according to the quality of the sample employed. The SECRETARY exhibited a piece of sheet copper, very much corroded, which was sent from Nova Scotia by Professor How, and which, being a portion of a metal chimney, showed the result of eighteen years' exposure to the products of combustion of wood and coal. The third paper read was entitled "On the Absorption of Vapours by Charcoal," by John Hunter, M.A. It was devoted to the examination of the powers of absorption of different kinds of charcoal, and the author found that the dense carbon obtained from the shell of the cocoa-nut was pre-eminently endowed with this property, and with it several comparative trials were made under varying degrees of temperature. The saturation point of the carbon was found to be in every case diminished by increase of temperature, and of all the vapours examined that of methylic alcohol was the most freely absorbed, for no less than 155 volumes of that vapour at the temperature of 90° C. were condensed by one volume of cocoa-nut charcoal. The experiments comprehended the trial of the following vapours :-Water, bisulphide of carbon, alcohol, methylic alcohol, fousel oil, benzol, ether, chloroform, and acetic acid; and the author noticed that the absorption of vapour by charcoal always terminated in a much shorter time than in the case of the permanent gases, rarely, if ever, exceeding an hour in duration. Upon the invitation of the PRESIDENT, Dr. STENHOUSE said that he had paid attention to the practical use of charcoal as a means of purifying air, and had always found the dense varieties of charcoal to be the most effective on account of the smaller size of their cavities. He had never made exact experiments of the nature just now described by Mr. Hunter. The PRESIDENT then adjourned the meeting until Thursday evening, November 16. NEWS COLLEGE OF PHYSICIANS. "On Animal Chemistry." A course of Six Lectures by WILLIAM ODLING, M.B., F.R.S., F.R.C.P. Friday, May 12, 1865. LECTURE 6. (Continued from page 202.) I CAN scarcely venture to conclude this course of lectures on " Animal Chemistry" without a few words upon the influence exerted on tissue metamorphosis by those chemical agents which are usually included in the class of alterative medicines. Although our acknowledged ignorance of the mode in which medicines produce their effects is made a standing reproach to medical art only by those who, ignorant of their ignorance, wrongly conceive that in other scientific arts-that of the chemist, for example-the use of the different agents employed has really ceased to be empiric, and become dependent upon abstract principles, still it will not do for us to regard the observed actions of different medicines as ultimate facts with which we must ever rest contented, but rather as difficult problems inviting a more competent investigation, and destined some day or other to yield to our inquiries. The subject, however, is too remote from even the present widely-extended boundary of scientific knowledge-the path from the known to the unknown is yet too lengthy and intricate-to warrant us in expecting any immediate or, indeed, proximate resolution of the darkness by which we are surrounded. In the belief, however, that even a little gleam of light, insignificant in relation to more advanced researches, may not prove altogether worthless here, I beg to suggest the following points for your consideration. It will be found, I think, that those mineral substances which act more especially as alteratives actually are, and necessarily ought to be, characterised, not by their chemical energy, but by their chemical mobility; and I do not know that I can make my meaning better evident than by directing your attention to the chemical properties of iodine in comparison with those of its intimate congener, chlorine. As I shall presently show you, both elements possess in a striking degree the property of oxidising various substances which resist the action of ordinary oxygen; and this observation leads me to make a few preliminary remarks upon the process of oxidation in general. Thus, it is well known that many oxidisable bodies which are unable or scarcely able to combine directly with free oxygen, can nevertheless combine on the instant with oxygen that is already in a state of combination. It seems, indeed, as if the fact of previous combination conferred upon the transferable oxygen a greater activity or tendency to unite with other bodies. Of this peculiarity of behaviour, the non-oxidation or slow oxidation of sulphurous acid H2SO,, into sulphuric acid H2SO by mere exposure to oxygen or air, and its rapid oxidation by means of certain hyperoxygenised compounds, such as the peroxides of hydrogen and nitrogen, affords us an excellent illustration. I have here a freshlymade solution of sulphurous acid, and to it I add a little chloride of barium, which, you observe, does not in the least disturb its transparency, thereby showing its freedom from any trace of sulphuric acid. I now draw a rapid current of air through the mixed liquid, but with no obvious effect. The sulphurous acid and oxygen, despite their agitation together, remain sulphurous acid and oxygen, instead of combining with one another to form sulphuric acid. Accordingly, we have not a trace of sulphuric acid produced sufficient to afford even a turbidity with the previously added barium-salt, although, indeed, by a prolonged agitation with one another, some sulphuric acid would be slowly formed. I now divide the mixed solution of sulphurous acid and chloride of barium, and add to one portion a little peroxide of hydrogen, when immediately we get a copious white precipitate of sulphate NEWS of barium. The sulphurous acid which would not unite with the free oxygen of the air unites at once with the combined oxygen of the peroxide, thus: Sulphurous. Hydric-perox. H2SO3 H20.0 = H2SO4 + H2O. The second half of the liquid I now pour into this bottle, charged, as you see, with brown fumes of peroxide of nitrogen, and agitate the whole for an instant or so, when the rapid oxidation of the sulphurous acid is rendered evident, in this as in the former experiment, by an abundant precipitation of sulphate of barium, while the brown peroxide is simultaneously reduced to the state of colourless oxide of nitrogen, thus : Sulphurous. Nitric perox. Sulphuric. Nitric oxide. H2SO3 + NO.O = H2SO4 + NO. The peroxides of hydrogen and nitrogen, therefore, act upon sulphurous acid in a precisely similar manner; but we shall find a great difference of behaviour in the monoxides resulting from their respective deoxidations. Thus, the oxide of hydrogen or water is a far more difficult substance to peroxidise than sulphurous acid itself. It is only, indeed, by a series of indirect processes that we are able to fasten on to its molecule an additional atom of oxygen, so as to convert it into the peroxide, and this added atom of oxygen is retained with such a feeble force that it is frequently thrown off in the free state, and constantly given up with the greatest readiness to any oxidisable substance, such as sulphurous acid. Although, therefore, it seems strange that sulphurous acid should not readily absorb oxygen from the air, there is nothing strange in its taking away the additional loosely combined oxygen existing in peroxide of hydrogen. But the oxide of nitrogen resulting from the deoxidation of its peroxide is a very different kind of body. Of all compounds known to chemists it is the one which absorbs free oxygen with the greatest avidity. No sooner, for instance, do I open the stopper of this bottle than the contained nitric oxide which we reduced from the peroxide a few minutes ago combines at once with fresh oxygen from the air to become reconverted into the brown peroxide; and on now closing the bottle and agitating its contents, the sulphurous acid, which is of itself unable to combine directly with atmospheric oxygen, instantly robs the peroxide of nitrogen of the oxygen which it had absorbed directly from the atmosphere, as in the ordinary manufacture of sulphuric acid; thus: Sulphurous. Nitric perox. H2SO3 + NO2 = H2SO3 Sulphuric. Nitric oxide. as a As remarked by Laurent, "There is no substance which presents such singular properties as nitric oxide. It is, perhaps, the only body which, in the dry state and at the ordinary temperature, can combine suddenly with oxygen. The combination, moreover, takes place without the evolution of heat, and the body which results, far from retaining the oxygen that it has so readily absorbed, is perhaps of all bodies the one which is deoxidised most easily." Nitric oxide and peroxide, then, are the types of chemically mobile compounds. Regarded reducing agent, there are many more powerful deoxygenants than the oxide, regarded as an oxidising agent, there are many more energetic oxygenants than the peroxide, but there are no two associated bodies known to chemists which respectively absorb or evolve oxygen with so much facility. Now, while chlorine may be compared to peroxide of hydrogen, it is the sort of chemical mobility manifested by the oxides of nitrogen, which is characteristic of iodine, and, I believe, of most mineral alteratives. Iodide of hydrogen or potassium is, like nitric oxide, a facile reducing agent, and free iodine or hypoidite of potassium, like peroxide of nitrogen, a facile oxygenant -so that wherever the iodine travels it is capable of influencing the processes of oxidation there going on-absorbing oxygen where there is excess, delivering active oxygen where there is deficiency-just as our nitric compound absorbs oxygen from the air and delivers it up to the sulphurous acid. tions. It is this mobility of iodine, then, which distinguishes it chemically from its more active congeners, chlorine and bromine. The general chemical relationship of these three elements to one another is most striking, so much so, indeed, that they might almost be regarded as mere varieties of the same primitive matter. With the probable exception of fluorine, they are the only elements which have the property of uniting with hydrogen in the proportion of volume to volume,-the combinations, moreover, being unattended by any condensation. Again, the resulting compounds—namely, the hydrochloric, hydrobromic, and hydroiodic acids are all gaseous, all fuming, all soluble in water, and all producible by similar reac Another common property by which chlorine, bromine, and iodine are characterised is their marked acthat of oxygen under similar conditions. In my last lectivity when in the free state, which very greatly exceeds ture I showed you the violent action of chlorine on metallic copper, upon which ordinary oxygen is, as you know, almost without action; and I have only a few minutes back referred to the little effect exerted by free oxygen upon various oxidisable bodies. But chlorine, bromine, and iodine act upon different metals, pseudo-metals, and compounds with the greatest facility; and, indeed, several of the iodides contained in the London and British Pharmacopoeias are directed to be made by Lastly, treating the respective metals with iodine. all three elements are capable of acting as oxidising agents in cases where free oxygen is altogether, or almost, impotent. They contain no oxygen, it is true, and are, on the contrary, so far as our present knowledge goes, simple or elementary bodies. Nevertheless, in the presence of the hydrogen of the water, and so liberating its pre-comwater they act as very powerful oxygenants by uniting with bined and, consequently, active oxygen. Thus, on adding chlorine, bromine, and iodine respectively to the clear mixture of sulphurous acid and chloride of barium conimmediate precipitate of sulphate of barium from the tained in these three glasses, we have in each instance an oxidation of the sulphurous acid, just as in our former experiments with the peroxides of hydrogen and nitrogen, the reaction being as follows:Sulphurous. Water. = Chlorine. Sulphuric. Chlorhydric. H2SO + H2O + Cl2 H2SO + 2HCl. Here, again, I have three white magmas of protoxide of lead, with an excess of dilute alkali, exposed freely to the air. Now, although this protoxide does not absorb oxygen from the air, yet when treated with chlorine, bromine, and iodine, it is at once oxidised more or less completely into the brown peroxide, as you perceive, thus :Lead oxide. Water. Bromine. Lead peroxide. Chlorhydric. PbO PbO2 + H2O + Br2 + 2HBr. Lastly, I have in these three glasses some solution of blue indigo exposed to the air, but unoxidised by the air. On adding chlorine, bromine, and iodine, however, it is at once bleached or oxidised into isatin, thus :Indigo. Water. Iodine. Isatin. Iodhydric. C,H,NO + H2O + I2 CH,NO2 + 2 HI. In all these particulars, then, chlorine, bromine, and iodine, though so different in their medicinal action, resemble one another to the greatest extent chemically. Now let us see what are their chemical, and. I may add, physical differences. I will first advert to their combining proportions, or the relative weights of each of them, which unite with 1 part by weight of hydrogen. indicated by the numbers 35'5, 80, and 127, which also = These are Chemically, then, 58.5 parts of chloride of sodium are just as efficient as 166 parts of iodide of potassium; but while most of us, suppose, are in the habit of taking fifty or sixty grains of common salt twice or three times a-day, few of us, I conceive, would like to take 166 grains of iodide of potassium even once in the same period. Now, the gradational difference subsisting between the atomic weights and volume-weights of chlorine, bromine, and iodine is typical of all their chemical and physical differences. Thus, their usual states of aggregation, gaseous, liquid, and solid, and the colours of their respective gases or vapours, green, orange, and violet, are sequential to one another; while, in a chemical point of view, we notice a successive decrease of the force with which they respectively enter into and remain in combination with other bodies. Thus, chlorine combines directly with hydrogen upon simple exposure of the mixed gases to ordinary daylight, and the resulting chlorhydric acid is an extremely stable body. But the direct combination of bromine with hydrogen takes place very imperfectly, and then only at a red heat, while the bromine of the resulting compound is liberated with very great ease. Further, the direct combination of iodine with hydrogen is almost impracticable, while the iodhydric acid resulting from the indirect combination of the two elements is gradually decomposed even by the action of atmospheric oxygen, thus: 2 HI+0=H2O+I2. The amounts of heat given out by the combinations of the respective halogens with hydrogen, which are, of course, the measures of the forces required to pull apart the resulting compounds, have not, I believe, been exactly ascertained, though they are obviously sequential, as in the case of the amounts given out during the similar combinations of the halogens with some basylous metals. Thus, when zine, for instance, combines with an equivalent of chlorine, the amount of heat evolved is nearly twice as great as that produced during its similar combination with an equivalent of iodine; or, in other words, the force with which zinc and chlorine are held together, and consequently the force required to pull them asunder, is nearly twice as great as that with which zinc and iodine are intercombined. Now, it is this feebleness of the force with which iodine enters into combination, and consequent facility with which it is separated from its combinations, that gives to it that peculiar mobility to which I have already adverted. The chief chemical difference, indeed, between chlorine and iodine seems to be that chlorine in the free state is far more active than iodine, and iodine in the combined state far more mobile than chlorine, while bromine occupies an intermediate position. Hence, on adding a little bromine water to the solution of iodide of potassium, the bromine expels the iodine, KI+ Br= KBr+I; which, dis solving in the chloroform I had previously introduced, manifests itself to you by the production of a beautiful violet-coloured stratum at the bottom of the tube. Similarly when I add a little chlorine water to this solution of bromide of potassium, the chlorine expels the bromine KBr+ Cl = KCl + Br, which dissolving in the previously introduced ether, floats on the surface as an orange-brown layer, so that while bromine expels iodine, chlorine expels bromine, and à fortiori iodine, from their respective combinations. Accordingly, we may regard 35'5 parts of chlobut it is this very energy of chlorine, I conceive, which rine as an energetic representative of 127 parts of iodine; disqualifies it for acting medicinally as an alterative. On account of its intense chemical affinity, it unites more rapidly and forcibly than iodine with the different basyloids it may chance to encounter, but directly it has entered into combination with them its work is done, its action ceases. The resulting chloride of sodium, or other chloride, is of so stable a nature as to be impressionable only to violent chemical agencies; whereas, iodine, on the other hand, forming very unstable compounds, is constantly, with every change of circumstance, entering into a fresh state of liberation or combination-constantly effecting fresh oxidising or deoxidising actions. I have already given you several illustrations of the oxidising action of free iodine, and ought, perhaps, to mention one or two instances of the correlative deoxidising action of combined iodine. For example, when tartaric acid is heated with aqueous iodide of hydrogen or iodhydric acid, it is converted into malic acid with liberation of iodine, thus :— = Water. Iodine. Tartaric Acid. Iodhydric. Malic Acid. 2HI C1HO+ CHO5 + H,O + I, Similarly the malic and fumaric acids are reducible into succinic acid by means of iodhydric acid, thus:Iodhydric. Succinic. Malic. Water. Iodine. CHO + 2HI CHO4 + H2O + Ig. = Fumaric. Iodhydric. Succinic. Iodine. = C1H2O1 + 2HI CHO, + I Accordingly, we find that while free iodine, acting as an oxidising agent, produces iodhydric acid, this same acid, acting as a deoxidising agent, reproduces free iodine. Here, for instance, I have some iodhydric acid mixed with a little starch, to show the result of the reactions. I now add to the iodhydric acid some peroxidised substance, which it immediately reduces with liberation of iodine, as shown by the blue colour of the liquid. I now add to the free iodine some suboxidised substance, which it immedi ately oxidises with reconversion into iodhydric acid, as shown by the disappearance of the blue colour. On now adding some more of the peroxidised substance, I re-liberate the iodine, and, on afterwards adding some more of the suboxidised substance, I reproduce the iodhydric acid, and so on ad infinitum. The characteristic chemical property of iodine consists, therefore, in the comparative feebleness of its affinities, or in the loose state of combination with which it is capable of being retained by other bodies; so that, while the more energetic chlorine acts once for all, the less energetic iodine is acting and reacting upon every occasion. Accordingly, while it makes all the difference whether we employ free chlorine or chloride of sodium to produce the therapeutic effects of chlorine, it makes very little difference whether we employ free iodine or iodide of potassium to produce the therapeutic effects of iodine. Wherever the element travels, it either oxidises or deoxidises, accordingly as it comes into contact with bodies more or less oxidisable than itself, at that particular moment. It acts, in fact, not only as a converter of inactive or free into active or combined oxygen, but also as a conveyer of oxygen from wherever it is in excess to wherever it is in deficiency. Now, what is true of iodine and its compounds is also true of the compounds of mercury, of arsenic, and of another metal whose alterative action is manifested in |