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subsist between hydrochloric acid, water, and ammonia; and in particular I have shown you that some of the best known products of tissue metamorphosis are in reality only the ammoniated forms of comparatively well known bodies. In my next lecture I shall endeavour to satisfy you that the complex character of many organic bodies is more apparent than real, and that most of them may be resolved into comparatively simple molecules, which are capable of being distributed into certain well defined groups and series; and I shall take, as a concrete illustration of the point I wish to establish, the composition of salicine among vegetable, and of hippuric acid among animal products.

ON LECTURE ILLUSTRATIONS.
By A. W. HOFMANN.

A Discourse Delivered to the Members of the Chemical
Society, Thursday, February 2.

(Reprinted by permission of the author from the Journal of the Chemical Society, Ser. 2, vol. iii., p. 156.)

In

THE introduction into modern chemistry of the idea of structural types, and the prominence given thereby to volumetric considerations, involve the necessity of modifying, to a certain extent, our present style of experimental illustrations. This necessity, I believe, has been felt by many teachers who have endeavoured to reflect the present aspect of chemistry in their lectures. these endeavours many new and interesting experiments must have been devised already; and if an interchange of the valuable information thus acquired could be effected, a large expenditure of time and labour would be saved to those engaged in teaching chemistry. The Chemical Society, comprising as it does a great many professors of our science, appears to be an appropriate centre to attract this floating knowledge for condensation and distribution. It is in the conception of this mutual benefit which we might derive from communications of this kind, that I venture to submit to the Society an account of some of the volumetrical experiments on the composition of the typical hydrogen compounds, with the study of which, during the last few years, I have been in the habit of opening my course of lectures on experimental chemistry.

HYDROCHLORIC ACID.

The usual method of illustrating the composition of hydrochloric acid, recommended in Manuals on Experimental Chemistry, consists in introducing a small ball of sodium into a volume of the gas, contined over mercury. Since the metal has to be heated, the upper part of the tube is bent (cloche courbe). It need scarcely be mentioned that a vessel of this form is very little appropriate for comparing the volume of the hydrochloric gas with the volume of the hydrogen gas evolved by the action of sodium; hence the necessity of measuring the gas in a graduated tube, of transferring it to the cloche courbe, and of re-transferring it to the graduated vessel, after the action has taken place. The experiment thus becomes tedious, difficult, and inaccurate. Again, how is it possible to introduce the metallic sodium into the gas without its surface having become oxidised? Not to speak of the rapidity with which the metal is amalgamated during its passage through the mercury.

By adopting the following mode of proceeding these difficulties are in a great measure obviated.

A U-shaped glass tube, about 50 centimetres long by 15 in diameter, having one sealed and one open limb, is fixed upon a convenient stand. Just above the bend of the tube, the open limb has a small outlet tube (blown on at the lamp), and to this is affixed a piece of caoutchouc tubing, with an elastic wire nipper (nipper-tap) attached, or provided with a screw (screw-tap), by the action of which the caoutchouc tube is pinched close, but can be readily opened at pleasure.

This apparatus has to be filled with an appropriate volume of the gas to be examined. For this purpose the U-tube is first filled with mercury, and then the nippertap is set open, so as to afford a gradual exit to the metal in the open limb. The delivery-tube of a gas generating apparatus is then passed down the open limb to the bend of the tube, in such a manner that the gas bubbles up through the mercury into the sealed limb, from which, of course, the metal escapes as the gas enters FIG. 1. volume for volume. An appropriate quantity of dry hydrochloric acid gas having been thus introduced, the nippertap is closed, and mercury is poured into the apparatus, until it stands at the same level in both limbs. The space occupied in the tube by the gas is then marked in any convenient way; preferably by a caoutchouc ring slipped over the tube (Fig. 1).*

FIG. 2.

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That portion of the open limb which is unoccupied by mercury is then filled with sodium-amalgam, and the orifice of the tube is closed, either by the thumb, or more conveniently, by a glass stopper. The gas may now, by inclining the tube adroitly, be easily transferred from the sealed to the stoppered limb; traversing of course, in its passage, the column of sodium amalgam, and being thereby decomposed. To insure complete decomposition, the apparatus should be once or twice shaken, so as to bring every portion of the gas into thorough contact with the amalgam; after which, by reversing the previous inclination of the tube, the gas may be re-transferred to the sealed limb of the apparatus. On removing the stopper or thumb from the mouth of the open limb, the mercury falls a little therein, and may be further lowered by opening the nipper-tap. As soon as the mercury stands at a uniform level in the two limbs the gas is found reduced to exactly half its original volume (Fig. 2). The residuary gas is readily recognised as hydrogen, by transferring it to the open limb; or, the closed limb may be provided with a glass stopcock (see Fig. 11), and the hydrogen expelled by pouring mercury into the open limb. In either way the gas is found to be inflammable, and to burn with the pale flame of hydrogen gas.

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This experiment shows us that a given bulk of hydrochloric acid contains half that bulk of hydrogen. It only remains, therefore, to determine with what proportion, by volume, of chlorine, this bulk of hydrogen is combined in hydrochloric acid.

This we learn from a second experiment. We submit hydrochloric acid to electrolysis in any convenient appa

* The illustrations given in this lecture are taken from a little work shortly to be published, entitled, "Introduction to Modern Chemistry, Experimental and Theoretic: Lectures delivered in the Royal College of Chemistry, London."

July 28, 1865.

ratus which permits collecting the gases evolved during the process. At starting, the chlorine is almost entirely absorbed by solution in the surrounding liquid: nor is it till this is saturated that the chlorine begins to be manifested in a stream of bubbles, like those which, from the first, mark the escape of hydrogen at the opposite pole. At this stage of the process the delivery-tube of the apparatus is attached, by means of a caoutchouc connector, to a glass tube, about 40 or 50 centimetres long by 1'5 centimetre in diameter, drawn out, before the lamp, to a fine point at each end. This tube is thus filled with the mixture of hydrogen and chlorine evolved by the electrolysis of hydrochloric acid. In order to expel every trace of air, it is necessary that the mixed gases should be suffered to traverse the tube for a considerable time. To prevent the chlorine escaping into the air, the free end of the tube is connected with the lower part of an upright cylinder containing coke, moistened with an alkaline liquid capable of absorbing the chlorine. After the lapse of one or two hours the operation may be considered complete. The tube being now detached, its fine-drawn ends are immediately sealed.

water (the receptacle for which should be a tall glass
cylinder, to facilitate this part of the manipulation), until
the level of the liquid within and without the tube is
brought into coincidence. It is then found that the tube
is just half filled with liquid; in other words, that just
half its gaseous contents have been absorbed. That the
absorbed gas is chlorine is readily proved by the bleaching
effect exerted by it on the log wood solution.
FIG. 4.

The tube having been sealed at each end, its gaseous contents have next to be examined. For this purpose it is requisite to bring the mixed gases into contact with a liquid capable of absorbing the chlorine, but not the hydrogen. Water, of course, answers this purpose, but a little soda may be conveniently mixed with it to increase its absorptive power. Again, the addition of a vegetable colour-of an infusion of logwood, for instance-to tint the soda solution employed, is useful as a means of evincing the presence of chlorine by exhibiting its bleaching action on the colour, so soon as it comes into contact therewith. By plunging the sealed finely-drawn extremity The nature of the residuary gas is as readily demon. of the tube into a solution so prepared, and then breaking strated by immersing the tube more deeply in the surit off, the desired contact is effected, absorption begins, rounding liquid, then breaking off its upper finely-drawn and the liquid is seen slowly rising into the tube to occupy point and applying to the jet of gas, thus forced out by the space vacated by the absorbed chlorine. This absorp-water pressure, a lighted taper, when it immediately tion goes on very slowly, however, because of the extreme takes fire, and burns with the characteristic pale flame minuteness of the surface of fluid exposed to the gas in of hydrogen. the finely-drawn tube represented by the broken extremity. A great acceleration would evidently be obtained if the surface of contact could be extended; if, for example, we could wet the whole interior surface of the tube with the absorptive liquor.

FIG. 3. this object.
A very simple contrivance (Fig. 3) accomplishes

It consists of a caoutchouc connecter tightly fitted to the end of the tube, so as to cover and enclose its fine-drawn sealed neck. This connecter is provided with a small glass funnel, through which it can be filled with a tinted solution of soda; and has also a stop-cock, by which, when so filled, it can be closed. These arrangements being made, the fine-drawn neck is immersed in the solution, so that, on breaking it (Fig. 4), which the flexibility of the connecter allows to be easily done, the solution finds its way through the orifice into the interior of the apparatus. By suitably inclining this, the solution may be caused to extend in a film over its interior, so as to expose a widely-spread surface to the gaseous mixture. The absorption of the chlorine is thus made to proceed with greatly increased rapidity, as is evinced by the speedy ascent of a small volume of the liquid into the wide part or body of the tube. This accomplished, that end of the tube which is armed with the tap-funnel and its flexible connecter may be plunged under water, the connecter withdrawn, and the experiment continued in the ordinary way, by allowing the absorption to proceed, and the column of liquid to ascend in the tube till all the chlorine is absorbed. This is known to have taken place by the liquid ceasing to rise in the tube.

The tube is now to be more deeply immersed in the

These phenomena furnish a simple and satisfactory reply to the question left unanswered by our previous experiment. The action of sodium upon hydrochloric acid has taught us that 2 volumes of hydrochloric acid contain 1 volume of hydrogen; the electrolysis of hydrochloric acid proves that, to form hydrochloric acid, volume of hydrogen combines with 1 volume of chlorine.

I

The two experiments, taken together, supply us with the exact points of information which our previous investigation of hydrochloric acid left deficient; so that, summing up our previous and present results, we now possess a complete and irrefragable demonstration-first, that hydrochloric acid is composed of hydrogen and chlorine; secondly, that these two elements are its sole constituents; thirdly, that they are united in equal volumes to form it; and, lastly, that, in so uniting, they undergo no condensation, but produce a volume of compound gas equal to the sum of the volumes of its elementary constituents.

This last-mentioned fact-the union of hydrogen and chlorine without contraction or expansion-may be illustrated by another, and an equally conclusive, experiment. While the electrolytic apparatus, used in the experiment just made, is still evolving hydrogen and chlorine in the proportion in which the two gases exist in hydrochloric acid, we may replace the wide glass tube, previously used, by another tube of equal length, but of stouter glass, and of smaller bore, half a centimetre being a convenient diameter. The two ends of this tube are, like those of the tube used in the previous experiment, drawn out into very fine necks. As soon as the tube is thoroughly purged of air, and exclusively filled with the gaseous constituents of hydrochloric acid, its fine necks are sealed by the blowpipe jet, and its contents are exposed to the action of light

for the purpose of inducing the combination of the mixed gases.

This effect, as is well known, may be obtained either by natural or artificial light. The direct rays of the sun produce instantaneous combination. But as such rays are not at our command in all seasons and at all places, as, for instance, during the earlier weeks of a London winter, it is necessary to employ an artificial light sufficiently intense to bring about the same effect. Such a light is that of the blue flame produced by the combustion of bisulphide of carbon in nitric oxide. The manipulation for generating this light is very simple.

For this purpose some eight or ten cubic centimetres of bisulphide of carbon are introduced into a tall glass cylinder filled with nitric oxide gas. This is most conveniently accomplished by means of a very thin bulb of glass, blown to the required size, filled with the bisulphide, and then sealed at the lamp. The glass cover of the vessel, already filled with nitric oxide gas, is drawn aside, the bulb drawn in, and the cover quickly replaced. Contact of atmospheric air is thus almost entirely obviated. The vessel is then shaken, so as to break the glass bulb, and the desired mixture of gas and vapour is at once obtained. A match is now applied to the opened mouth of the cylinder, when the mixture within takes fire, and burns with a brilliant, intensely blue flame, which descends into the vessel. The radiance of this light instantaneously induces the combination of hydrogen and chlorine; the effect being indicated by a flash of light, accompanied by a slight clicking sound, and followed immediately by the disappearance of the greenish colour of the mixture."

The figure (5) shows the disposition of the apparatus. To the left is the glass cylinder in which the light is generated; to the right are placed the mixed gases to be acted on, two tubes instead of one being filled therewith and employed in the experiment, to afford a double chance of success, since the combination occasionally fails from causes not yet perfectly ascertained. FIG. 5.

For the purpose of examining the product, one point of the tube is broken under mercury, when the first indication is immediately obtained. It is observed that neither does gas escape from, nor mercury penetrate into, the tube;

from which it is clear that the combination of the gases has taken place without either contraction or expansion of their volume.

The next indication is obtained by pouring water on the mercury, and raising the tube so that its orifice, instead of plunging into mercury, may open into water. The water no sooner comes into contact with the gas than this latter is dissolved; and so rapid is the absorption that the water rising in the tube fills it almost instantaneously. We thus obtain an additional experimental proof that hydrochloric acid is formed by the union of hydrogen and chlorine gases, in equal volumes, without condensation. In performing this experiment, whether sunlight or the light of bisulphide of carbon be employed, some manipulatory precautions are necessary to shield the operator from possible injury by the explosion of the tubes. The experimentalist should not omit to protect himself by a screen, for which purpose a sheet of stout plate-glass may be conveniently employed. Thus, even should the tube explode, the dangerous scattering of its fragments is prevented. It is, however, only rarely that the body of the tube is shattered; in most cases the fracture is confined to one or other of the sealed points. To avoid the loss of the experiment by an accident of this kind, the upper point of the tube may be strengthened by imbedding it in sealing-wax, which may be most conveniently applied by fusing a little in a small piece of glass tube sealed at one end, and plunging the point to be protected into the fused mass, which is then allowed to cool and harden. As for the lower point, escape of gas from this, in case of rupture, is readily obviated by keeping it immersed in a troughcylinder filled with mercury.

WATER.

in water is, of course, most conveniently established by The ratio in which hydrogen and oxygen are associated the electrolysis of this compound.

Among the numerous contrivances used for decomposing water, an apparatus constructed some time ago by Professor Buff, of Giessen, deserves to be especially mentioned. The two tubes for the collection of the gaseous constituents of the water are provided with brass stopcocks, and plunged into a deep cylinder filled with water. As the gases are evolved, the water-level in the tubes is depressed below the level in the cylinder, and on opening the stop-cocks, the gases escaping under the pressure of the short water column may be conveniently examined.

Fig. 6 shows an improved form of this apparatus. Instead of the two stop-cock tubes separately inverted in a basin, as just described, I have adopted a three-branched tube, with one long and two short limbs. The long limb acts as a water-reservoir, instead of the basin; the two short limbs, which are fitted with stop-cocks, or nippertaps, above, and which communicate freely with the long limb below, contain, intermediately each a platinum electrode. When this apparatus is used, the water in the short limbs is forced downward out of these so as to rise in the long limb, forming a column, the weight of which serves afterwards to expel the gas from each short limb through the corresponding stop-cock, when this is opened for the purpose of testing the nature of the gas obtained.

It now remains only to be demonstrated that two volumes of hydrogen and one volume of oxygen, when combined, yield two volumes of water-gas. This fact, familiar to us from the earliest stage of our chemical education, is, strangely enough, scarcely ever demonstrated by experiment in our lectures. As to myself, I have only since the volumetric conception of matter has acquired such predominant importance, commenced performing this experiment.

The object to be achieved is the comparison of the volume of the elementary water-constituents with that of the water formed, at a temperature high enough to maintain the latter in a purely gaseous condition.

The experiment is made in a U-tube similar to that used

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in analysing hydrochloric acid. The closed limb of the tube is, however, fitted, at a point near its sealed extremity, with two platinum wires, for the purpose of passing the electric spark; this operation I now invariably perform by means of the induction-coil.

A glance at Fig. 7 shows how this apparatus is employed. Into the sealed limb of the apparatus, which is filled with mercury, we admit a column, about 25 or 30 centimetres high, of a mixture of hydrogen and oxygen in the proportions in which they form water. This mixture may, of course, be obtained by adding two volumes of hydrogen to

one of oxygen; it is, however, prepared much more readily in due volumetric proportion, and in a state of perfect purity, by the electrolysis of water. The gas-filled limb of the apparatus is surrounded by a high glass cylinder, the lower mouth of which is fastened around it by means of a perforated cork, whilst its upper mouth (likewise closed by a cork) rises about five centimetres above the sealed extremity. The annular space thus formed communicates, at its upper end, by means of a bent glass tube and a perforated cork, with a flask which contains a liquid having a boiling point considerably above that of water; amylic alcohol, which boils at 132° C., is well adapted for the experiment. On protracted ebullition, the vapour descends from the flask into the annular space, which rapidly acquires a uniform temperature of 132°. To prevent the vapours from escaping into the atmosphere, the lower extremity of the glass cylinder is connected with an appropriate vapour-condenser, such as a glass coil kept cool by water. Under the influence of heat, the column of mixed hydrogen and oxygen in the tube expands. The level of the mercury in both limbs of the apparatus having been adjusted, the height of the gas columns is now marked by any suitable means; preferably by slipping a caoutchouc ring over the outer glass cylinder. A little more mercury is then poured into the open limb, which is, lastly, closed by a well-fitting cork. Between this cork and the mercury intervenes a column of air, some eight or ten centimetres in length, and capable of yielding to pressure, like a spring. It now only remains to inflame the gaseous mixture by causing the current of the inductioncoil to leap, in the form of a spark, between the platinum

points. The gases combine with an explosion, which is, however, much mitigated in violence by the elastic action of the above-mentioned air column. At the high temperature employed (1320) the water formed retains the gaseous condition. On removing the cork, and allowing the mercury to flow through the nipper-tap, until it is level in both limbs, it becomes obvious that the original measure of mixed gases is diminished by one-third; the residuary twothirds are water-gas, which condenses into liquid water so soon as the apparatus is allowed to cool.

Thus, therefore, it stands experimentally demonstrated, first, that hydrogen and oxygen undergo condensation in combining to form water; and, secondly, that the volume of the water-gas produced holds an extremely simple ratio to the volume of its constituent gases, two volumes of hydrogen and one volume of oxygen condensing, by their union, into two volumes of water-gas. (To be continued.)

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ACADEMY OF SCIENCES.
July 17.

M. TROOST communicated some "Researches on Zirconium." To obtain crystallised zirconium, the author heated in a retort-coke crucible to the temperature of melted iron a mixture of the double fluoride of zirconium and potassium and metallic aluminium. When the crucible was cold the surface of aluminium was found covered with crystallised lamellæ, lying one on the other, like the leaves of a book. There were crystals of zirconium. This element also exists

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A Letter to the Members of the British Medical Association on the Subject of their Future Journal. By R. B. CARTER, F.R.C.S., etc. London. 1865.

THE author of this letter is of opinion that, to advance the interests of the medical profession, it is advisable that the British Medical Association should give up their present Medical Journal, and publish a 66 Quarterly Journal of Literature, Science, and Politics." He complains that the educated public do not sufficiently appreciate the Profession, which he says has no means of influencing public opinion, and he thinks that by establishing such a journal as that mentioned above, and by dosing the public (gently at first) with medical topics, they might be gradually brought to entertain sound views on the rights, dignities,

and duties of Doctors.

As the Association is just about to meet, and the change suggested in this letter will be discussed at the meeting, we may, perhaps, as part of the public, be allowed to say a word on the matter. We say, then, that to medical politics we are profoundly indifferent. What we do feel an intense and personal interest in is the progress of the "healing art," and we believe that just as the knowledge of this is advanced, the medical profession will rise in public estimation. The question that the Association should discuss then, we think, is this,-What journal will

NEWS

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is then added in small quantities, so that the temperature is not much raised. The liquor is filtered from the chloride of sodium, and rectified by distillation. The properties of phosphoric ether are well known to our readers.

The title of a paper by Carius sufficiently describes its contents: "On the Occurrence of Casium and Rubidium in Plutonic Silicates of the Rhine Provinces."

In a note "On a New Transformation of Leucin," Dr. Kohler makes known that, when leucin is treated with dry hydrochloric acid, an atom of water is eliminated, and a new body formed, which the author proposes to call leucinimid. In the next paper Dr. Preu shows that when alanin, an analogue of leucin, is similarly treated, the same change takes place, and lactimid is formed. A notice by Martius and Griess, “On a Compound from Naphthaline Isomeric with Alizarin," describes the compound mentioned in our reports of the Academy of Sciences naphthalic acid) whose account in the Comptes-Rendus is as discovered by MM. P. and E. Depouilly (chloroxymuch fuller than that given here.

The other papers in this journal call for no notice.

NOTICES OF PATENTS.

best aid in developing and diffusing among the members GRANTS OF PROVISIONAL PROTECTION FOR sound scientific information on the art of curing disease?

A Course of Practical Chemistry; arranged for the Use of Medical Students. By WILLIAM ODLING, M.B., F.R.S., &c., &c. London: Longman and Co. 1865. Second Edition.

THIS is the second edition of a good book now greatly enlarged and improved. It is said to be specially arranged for the use of medical students, but, we need hardly say, it is equally well adapted for pharmaceutical chemists, and is indeed an excellent introduction to analysis for any students. It is worth mentioning that "the old scale of atomic weights has been exclusively employed throughout the body of the work ;" and that a very useful chapter on Chemical Manipulations, which greatly increases the value of the book, now precedes the analytical part.

6

39

Annalen der Chemie und Pharmacie. June, 1865. HLASIWETZ AND BARTH continue their chemical studies "On Resins," describing in this article the decomposition products of the action of fused alkalies on resins. They have experimented upon benzoin and dragon's blood, and also upon socotrine aloes. All these bodies, when fused with caustic potash, give paraoxybenzoic acid, II,3, aloes yielding the largest proportion. Dragon's blood yields, in addition, some benzoic acid, protocatechuic acid, and phloroglucin. Benzoin also gives protocatechuic and oxyphenic acids. The authors append to their paper a table of the composition of guaiacum, dragon's blood, gum, benzoin, galbanum, and aloes, the products of their dry distillation, and the results of their oxidation by potash. We hope to find room for this table at a future time.

A paper by Otto describes the "Products arising from

SIX MONTHS.

Communicated by Mr. VAUGHAN, PATENT AGENT, 54, Chancery Lane, W.C.

1585. E. T. Hughes, Chancery Lane, "Improvements in the means of producing from rosaniline blue and violet colouring matters soluble in water." A communication from P. Mounet, Lyons.-Petition recorded June 12, 1865.

1703. C. Worssam, Kingsland Road, and G. Evans, Gloucester Place, Portman Square, "An improved pulping and compressing machine for the treatment of peat as a fuel and gas for illuminating purposes."-June 26, 1865.

1716. H. G. Fairburn, St. Luke's, Middlesex, "An improved mode of combining and forming small coal or coal dust into lumps, blocks, or otherwise, to be employed for the purposes of fuel."-June 28, 1865.

1785. C. F. Claus, Fearnhead, Lancashire, "Improvements in obtaining sulphates and carbonates of potash and soda."-July 6, 1865.

1793. J. M. Macrum, Hill Street, Knightsbridge, "Imtion from J. Williams and J. Copley, Allegheny, Penn., provements in the manufacture of iron." A communicaU.S.A.

improved portable pocket gas-generator or gazogene." 1795. A. F. Morelle, Boulevard Sebastopol, Paris, “An

Little Horton, Bradford, "Improvements in manufacturing 1797. J. Peel, Bowling, Bradford, and W. Hargreaves, grease from soap suds."-July 7, 1865.

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the production of artificial light and in the apparatus con1809. J. Baggs, Chancery Lane, Improvements in

nected there with."

the manufacture of cast steel."-A communication from 1813. R. A. Brooman, Fleet Street, "Improvements in C. Pauvert, Tarbé, France.-July 8, 1865.

1831. H. A. Dufrené, Rue de la Fidélité, Paris, "ImA communication from Viscount C. de Sequeville, Milan. provements in the treatment of copper and nickel ores.'

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