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Royal Institution of Great Britain.

face of the glass and arrived at the lower surface, it does not all escape through to the air, some is reflected back again, although the greater portion is refracted through the surface below. Now, wherever you have refraction you always have reflection. There is, therefore, reflection at the bottom surface as well as the top, and thus you have two beams reflected instead of one. In fact, supposing this to be the outline of our plate of glass,

{CHEMICAL NEOUS

Jan. 25, 1862.

This

particle of ice to the particle of air, there is a little reflection, that the snow becomes an opaque body; and if you observe snow after it has fallen, upon the mountains of Switzerland, and has had the air squeezed out of it by the enormous pressure of the superincumbent mass, you will find it is actually converted from white snow into beautiful pure, transparent ice. To make an experiment to illustrate this, I will take first a piece of bibulous paper. paper was once a pulp or jelly, as you know, and was partially transparent, because the fibres of the paper were then mixed up with water, and in passing from the fibre to the water there was not much light lost. These fibres are little transparent threads, and in the case of this paper they are separated from each other by little interstices filled with air; in passing from one fibre to the air, and from the air to the next fibre, there is reflection of light; and this occurs so often that the paper is converted into an opaque substance. If, instead of having air between the fibres of the paper, I throw between them a liquid which has almost the same power of refraction as the fibres themselves, then I destroy this reflection, in virtue of which it is rendered white, and I think you will see when I make use of such a liquid that I powerfully augment the transparency of this paper. That simple experiment when you dip your towel in the basin in the morning, is extremely full of philosophy; the towel becomes darker because the interstices are filled with water instead of air, and becomes more transparent. I have here some of the bibulous paper. Mr. Anderson will give me a little olive-oil, a substance possessing pretty nearly the same refractive power as the fibres of the paper. I will dip a rod of glass into the oil, and cause a drop of it to fall upon the paper. First of all I cast the image of the white paper upon the screen. Having done that, I will show you how I at once augment the transparency of the paper if I allow a drop of oil to fall upon it. There is the oil trickling down, and you see how greatly the transparency is augmented by the saturation, the filling up of the little interstices of the paper with the oil, which possesses a refractive index very nearly equal to that of the fibres of the paper itself. Thus you see in this way we can render this opaque substance in some measure transparent: and this is the philosophy of the tracing paper used by engineers; they take tissue paper, saturate it with oil, dry it, and then place it upon their drawings; then they can easily see through it, and copy the plan underneath upon the tracing paper. These things have all their peculiar philosophy.

and supposing a ray of light (ab) to fall upon it thus, it is bent as you know towards the perpendicular, and on leaving the glass it is bent again from the perpendicular thus (b c, c d), but here (at b) there is a portion of light reflected, and here (at c) there is also light reflected. Another portion is reflected and refracted here also (at e), | and thus you get a series of reflections from the two internal surfaces of this piece of glass. When the piece of glass is thick you see the difference between those rays more strikingly than when it is thin. Take a lookingglass, and look very obliquely in it at a white object, you do not see one image merely. If you place a candle near the surface of that looking-glass and look at it in the glass you see a series of images. First of all, you have a tolerably bright image, then a very bright image, then the rest get dimmer and dimmer till they actually become too dim to be seen. The first image you see, which is rather bright, is the one reflected from the first surface of the glass, the second, which is extremely bright, is from the silvered surface behind, and then you get a series of reflections from side to side. I have here such a piece cf glass, and will make the experiment with the help of my lamp, and will show you these images obtained at the forward and the backward surface of the looking glass. If I cause a beam of light to strike obliquely upon this glass you see first of all an image reflected from the anterior surface, and then you see further on another very bright one reflected from the silver surface, and next you have a series of images becoming gradually fainter and fainter until they are invisible.

Now, I want to turn for a moment to another matter of some importance. I have said, that wherever you have refraction you have reflection, and if you have no refraction you have no reflection. Take a liquid and a solid; no matter how different the solid may be in substance from the liquid, no matter how much heavier, if it only bends a ray of light to the same degree as the liquid, it acts just the same as the liquid itself, and becomes invisible when it is plunged into it, owing to the absence of refraction and reflection at the two bounding surfaces. I have said in the memoranda that if you plunge the eyeball of an ox into water, it vanishes; it appears like the water, although it is a totally different substance.

When light passes from one medium to another of a different refrangibility, there is always reflection. And thus, if you mix two transparent bodies together, having different powers of refraction, the reflection may occur so often as to render this mixture perfectly opaque. Thus foam-which is only water-is as white as snow; and if I take snow itself, its particles are perfectly transparent, but it is because the particles of ice have air mixed up with them, because when the light passes from every

Let me now go on to the more immediate subject of this day's lecture. I have said at the commencement of the list of memoranda that when a ray of light passes from a rarer medium to a denser it is bent towards the perpendicular. You must not, however, imagine that the heavier the body the more power it has to bend a ray of light. That is in a great many instances the case, but not always, as I will prove to you. For instance, I have here a cell, and this cell contains two substances perfectly transparent, one floating above the other. The under liquid is water, the top is turpentine. The spirit of turpentine you see is lighter than the water, and is therefore less dense. It floats upon the water; but still you will find that it will bend the ray more than the water, notwithstanding its being less dense. We will make our experiment in the usual way. I will project its image on the screen, and you will see very clearly the limiting surface between the turpentine and the water. There is a little undulation of the surface caused by the motion, and you see our beautiful beam divided by a thin dark line which corresponds to a portion of light reflected by that surface. is at present going straight through; but I will turn my cell so as to cause the beam to fall obliquely upon both liquids (and remember, the image is inverted, the turpentine, which is really at the top, appears at the bottom; the

The beam

eell being apparently turned upside down, as I have already explained to you), when, if the turpentine, the lighter liquid of the two, possesses a greater power of refraction than the water, its image will move the most. When I move the cell obliquely you see that the line of continuity is immediately broken, and it is perfectly manifest that the lower image is moved further than the other, and if I turn it in the other direction you will have the same result, thus proving that the turpentine has a greater power of refraction than the water, although it is less dense. Hence, when we speak of one body being denser than another in optics it will not do to affix the ordinary idea to the term dense. What is meant by a dense body in optics is one which refracts the light powerfully; and when one body refracts more than another it is the denser of the two.

Let me pass on to another very important portion of our subject, and that is the subject of total reflection. This is very important, and is capable of being understood by all of you. I will suppose this to be a vessel containing water, this (ab) being the surface of the liquid. We know

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a little triangular glass prism, polished on the sides and face. Suppose a ray of light were to strike straight against the

surface (c) in the direction (a b), then it so happens that in the case of glass it meets it so obliquely that it is totally reflected downwards or upwards, as the case may be. I think I cannot do better than show you the total reflection of the image of the coal points, which you know so well already. There you see that beautiful image, and I will let the ray strike right plumb against the face of the prism; it goes through and is reflected from the other, so that you will see the image of the coal points upon the ceiling. I will now send the ray of light in another way through the prism, parallel to the long surface; when it enters the prism it is refracted through the first surface, and strikes against the hypothenuse; it is there again totally reflected (see Fig.), and will quit the surface exactly at the same angle at which it entered. This is also a case of total reflection; when I turn the prism, you have the coal points turning round horizontally, one, as it were, attacking the other.

I will now direct your attention to another very interesting case of total reflection, a case which I intend to illustrate if I can by means of this apparatus. I have on this stool an electric lamp, and in front of it is a hollow iron vessel connected by a pipe with the water-pipes of the building, so that I can allow the water to enter it, and issue that if a beam of light fall upon the surface obliquely, it forth in the form of a jet from a hole near the top of the is bent down on entering. We also know that, supposing vessel. At the back, opposite the hole from which the we had a luminous point (at c) underneath the surface, at vein of water will issue, there is a plate of glass, and I the bottom of the vessel, and a ray of light quitted that can send, as you will see immediately, a beam of light luminous point along this line (c d), it would on emerging from the electric lamp through this plate of glass and from the water be bent in this way (dc). Suppose straight through this vessel: I think you will see a cone a second ray of light starts from the bottom of the vessel of light passing through the hole and falling upon the part in this direction (f'd), it will be refracted on quitting the of the audience in front. I will now have the vessel water, thus (df). Supposing now I draw a third ray filled with water, and when the jet issues, the beams of (gd) starting from this point (9), a ray of light coming light that you saw striking against the audience will along that line (g d) would be bent so that it would just strike obliquely against the interior surface of that vein of cross the surface and emerge along the line (d g'). Now water. What is the consequence? They cannot get out supposing you come to a point beyond that ray (g d), of the vein, they will actually be washed down as if the which, when refracted, just crossed the surface, and sup light was a solid thing, and reflected from side to side, but posing a ray of light were to come up from that point (h) so obliquely that they cannot quit the liquid; and I trust to this (d). What would become of that ray? This one in that way to illuminate the vein of water from top to (gd) we suppose has just crossed the surface; this one, bottom, by carrying down the light which formerly passed then (hd), will not be able to get out of the medium at all, straight through. If I interpose a coloured glass the vein but will be totally reflected or thrown back along the line of water will be coloured. [The lecturer interposed glass (dh'); we have passed the limit of refraction, and got into of different colours, thereby colouring the vein of water.] the limit of what is called total reflection; the ray is So much then for this beautiful effect of the total reflection wholly driven back into the medium again, and cannot of light within the vein. escape from it. I find it so in this very turpentine; I look upon it and find that when a ray of light falls obliquely from the turpentine into the water, the light falling upon the surface is totally reflected, and communicates to it a shining metallic lustre. This is an experiment you can make for yourselves. Take a little water in a common glass tumbler of this kind, put a spoon in, and look at the spoon from beneath through the side of the glass; it is evident that the rays of light from the spoon strike against the upper surface of the water and cannot get out, so that you have a beautiful image of the spoon above. Put a shilling in the glass underneath the water, look from below at the surface, and you have a second splendid bright burnished shilling apparently floating upon the water above; because the rays of light, not being able to get out, are reflected back again and strike your eye, and thus you have it floating upon the surface of the water. I have here

You have seen that by the most simple arrangement of lenses we have obtained very beautiful effects; we have obtained images of medals and of these coal points by one simple lens. You know also that with a convex pair of spectacles we can obtain inverted images of candles or any other object sufficiently luminous to cast a reflection on the screen I am now about to show you one or two effects with an apparatus which is a little more complicated than the simple lens I have hitherto used. The apparatus I have in my hand depends upon the same principle as, but is much more refined than, the magic lantern. The magic lantern consists simply of two parts, one part to illuminate the object, and the other part to make a magnified image of that object on the screen. I have here the representation of a little boy who is brushing a boot. First of all I illuminate that boy by casting a beam of light on this glass transparency. The light goes through

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Royal Institution of Great Britain.

it, and then by means of this lens that you see here, I cast
an image of the boy on to the screen. The lamp does
nothing more than illuminate the thing. Thus I have
to all intents and purposes a magic-lantern. There
is the little fellow you see. We are not here merely
for the purpose of looking at those ridiculous
things, but for the purpose of knowing the principle
on which all these things, ridiculous and un-ridicu-
lous, depend. Here also we have
a microscope
formed by the combination of lenses. I can throw a powerful
light upon the object that I put between these two slides,
and thus illuminate it very powerfully. Here in front,
you see, I have a little system of lenses, by means of
which I shall get a very high magnifying power, and I
trust to be able to show you objects which would entirely
escape your power of sight if I made use of a lens of the
former kind. Every boy present must have seen those
figures that are not at all uncommon now in London and
elsewhere-those beautiful figures of the frost-those
beautiful crystals that are frequently formed upon the
surface of the window panes. I am sure those things are
worthy of every boy's attention, and not only worthy of
boys' attention, but worthy of men's also, for they are
among the most wonderful things in the world. We hear
people talking contemptuously of matter, and pouring
scorn upon matter; but these are only people who do not
understand matter. Matter, like everything else in crea-
tion, is glorious when you see its laws and phenomena
with a clear eye. Now, these little particles of water
have a power inherent in themselves of building them-
selves up in geometric forms when they are chilled-
when they are cold: they have the power of building
themselves up in these wonderful and beautiful crystals
that you see upon the surface of the window panes. I
have sometimes warmed a pane of glass on which those
crystals were deposited, and I have produced thereby a
liquid film all over the pane, and I have looked on that
film, and I have seen it just begin to move, and then the
little atoms have run together as if they were alive, and
have weaved a web of such beauty, that nothing man ever
did, or can do, can approach it, and still this is very
common. It is a thing occurring every winter, and I do
not know whether boys have ever sufficiently reflected
upon the marvellous beauty-upon the wonderful miracle-
that is involved in the formation of these splendid frost
crystals. There is not a bit of sugar-candy which you
suck which does not involve questions before which Sir
Isaac Newton, Mr. Faraday, or the wisest man who ever
lived, is a mere child-he absolutely knows nothing about
it; and yet we continue thoughtlessly to pass over these
beauties without opening the eyes of our minds to their
wonderful history. I will try now to show you a similar
case by freezing some other substance-not water, for I
cannot readily freeze water with a strong beam of electric
light upon it, but I will take some other substance that I
can freeze, or at least, try to freeze. In the first place it is
absolutely essential for this experiment that I should have
my plates of glass perfectly clean; and so I do not wash
them simply with water but first with strong solution of
potash. Mr. Anderson will now give me a solution of
sal-ammoniac; and this is the thing that I am going to
freeze or rather to crystallize :-freezing is a process of
crystallization, but you would not perhaps apply the term
freezing to this action. I have now a film of liquid upon
this glass plate, somewhat similar to that of water upon
the window pane, and I will try and introduce the plate
between those two slits and illuminate it by means of the
electric light and cast the image on to the screen. [The
experiment was then performed and in a few seconds the
crystals of sal-ammoniac were seen shooting into the field
of view.] There you see it, boys; look at those crystals
which are being formed, do they not march like an army;
the "atoms march in tune," as some poet says. The
process that goes on upon the window panes on a winter's

CHEMICAL NEWS,
Jan. 25, 1862.

| night is equally beautiful. There they are; how they rush like living things through the liquid! This then is one of the things that this beautiful microscope is capable of showing.

I will now go on to the consideration of another portion of our subject, and that is the most wonderful optical instrument of all-the human eye. You will understand the general structure of the eye in a moment. Cast your eye upon any one of those figures here [referring to Figures 1, 2, and 3.]

2

3

You have there the general structure of the eye, supposing it to be cut through, and that you look at the cut sideways. There is a thing just in front of the eye like a watch glass, called the cornea; it holds a little fluid called the aqueous humour and behind that there is a little lump of jelly-like matter called the crystalline lens; and it would really be worth while to get an ox's eye from a butcher and cut off the coat and get at this little lens. Behind is the general mass of the eye-ball, filled with what we call the vitreous humour. As I look at the audience, what takes place? Something that ought to excite your wonder and astonishment. When I look towards you, if any of you could get behind and look at the back of my eye you would see printed upon a little space at the back of my eye an image of the whole audience, some perfectly distinct, others not so distinct. Those that I look at distinctly are perfectly imaged. Now, there is another remarkable thing that instead of sitting upright, you are depicted in my eye sitting with your heads downward. Supposing that (No. 3) to be an arrow, the rays of light go through the pupil of the eye, through this round hole that you see in the centre, which is surrounded by what is called the iris. The light comes from the pupil thus, and the point of the arrow sends its light upwards, and the feather end sends its light downwards; so that you see the image of the arrow is inverted on the retina, as it is called,- -an extension of the optic nerve at the back of the eye.

I want to actually prove to you, by experiment, that that is the case,-a very rude experiment, indeed, but still a very instructive one. I have here tried to make an eye; it is a very large spherical glass vessel filled with water. You see I have surrounded it on one side with black paper. There is a hole in the paper which represents the pupil of the eye. I will place in front of that hole a crystalline lens and will allow the light to fall upon the lens and through the water. Here at the back there is a tracing paper screen sufficiently transparent to allow you to see an object through it. This tracing paper represents

NEWS

the retina. We will see if we cannot get an inverted image of the candle upon the retina. [A lighted candle was placed in front of the artificial eye.] There is the candle, and you see the image of the candle is inverted on the retina; we will throw a beam of light upon the candle so as to illuminate the stem of the candle, and then, I think, we shall see it still brighter. [This was accordingly done.] You see how finely shown it is: the candle is pretty visible from this point behind the tracing paper, and is inverted. Now, let me take something else; let the assistant go in front and I will illuminate his hands. There, you see the image, and if he puts his hand upright you will see that the image of the finger-nails will be down. In like manner if I take the dial of my watch you see I can throw its image on the retina, and a very beautiful object it forms. We have to bear in mind, first of all, that in order that an object may be seen with distinctness, the rays of light issuing from it must come exactly to a focus upon the retina. Now, what takes place really? Some boys' eyes very often have too powerful a refraction; they combine the rays of light here (No. 1) [indicating a spot between the crystalline lens and the retina]; and the consequence is they cause the rays of light to come to a focus before they reach the retina, and thus, instead of having a sharp point upon the retina, you have a blurred image as you saw there, when I did not hold the watch at the proper distance. Some eyes, especially old eyes, have not the power of converging the rays of light sufficiently, and what is the consequence? They do not come to a focus at all; the eye is unable to bring them to a focus on the retina; they converge towards a point behind the retina. This is a case of long sight. What does the boy do who is short sighted? He holds the object close to the eye, because he wants to throw the point of intersection back. He has to look closely at the object, and hence he is said to be "short sighted;" and such boys, if they ao not wish to look at the thing very closely, have to put a concave lens in front of the eye: this gives the rays a certain amount of divergence, and the focus is thrown back to the retina. On the contrary, those people who wish to bring this point of intersection forward must use a convex lens, as I have said. The eye has insufficient power to refract the rays. To help the refraction we place a double convex lens, or a plano-convex lens in front. I will show you these different lenses. Sometimes when I am tired I require to look through a pair of spectacles, and Mr. Anderson has given me the spectacles that he uses in this room, and here is another pair of spectacles that he uses for reading, or when he wants to see small objects. Now, I will show you the difference between these different glasses. I will take my own spectacles first. Here I want to show you, first of all, the convergence of the beam of light into the middle of the lens ; but look how far I have to go away in order to get a perfectly clear image of the coal points. They are quite small; but perfectly clear. Now I will take Mr. Anderson's least magnifying spectacles-those with which he looks at you, and there you see the image is very large-larger than mine. If I take this other pair of Mr. Anderson's -those which he uses to read by-you see for yourselves how large the image is. Many of you, I have no doubt, have fathers who use spectacles of this kind; borrow them and make this beautiful experiment for yourselves.

I will now say a few words on the effect of the impression made upon the eye. When a flash of light falls upon the eye, supposing that flash of light could pass away instantly it strikes the eye, does the impression vanish at the moment the light vanishes? No. Everything in nature takes time to subside; and the consequence is that if you take the burning end of a stick, and then cause it to pass slowly through the air, you can follow the point of that stick; but if you make it describe a circle in about the fifth of a second, you see that circle as a continuous line of light, because in point of fact the impression

remains upon the eye during the time the point goes round-that is, if it go round as quickly as I have said. If it travel round the circle in less than the fifth of a second, you find that it forms a continuous line. Now, instead of a burnt stick, I will take our lamp and I wilt try to show you this line of light on the ceiling. I will reflect this beam of light-this fine index you have therefrom a looking-glass, and if I am skilful enough in turning this, you see the light travel round and gives a single image. If it travel quickly enough you see a continuous ring of light, because every revolution is accomplished within the time that the image takes to subside; and thus, as I have stated in the list of memoranda, when a series of sparks follow each other in succession at intervals of less than the fifth of a second, the impression made by one spark remains upon the eye until that made by the next spark, and you see the succession of sparks as a continuous line. Here I have a beautiful case of this kind, which will show it to you very distinctly. Here is a system of tubes, and we have a little battery underneath the table, by means of which I can send an electrical discharge through them. [The experiment was then performed.] Here we have this beautiful effect; you see in each of these branches we have a continuous light. There is a series of discharges, and each single image corresponds to a single discharge. If I turn it at a certain amount of speed, y ou see that the wheel appears to be resolved into distinct spokes. Here you see [causing the branches of the apparatus to revolve rapidly] I have a star of light. This is owing to the continuity of the impression produced by the succession of these discharges.

Special General Meeting. Monday, January 13, 1862.

The Rev. JOHN BARLOW, M.A., F.R.S., Vice-President, in the Chair.

The following Address to Her Majesty, the Queen, in reference to the decease of H.R.H the Prince Consort, Vice-Patron of the Royal Institution, on December 14th last, was read and unanimously adopted:—

TO THE QUEEN'S MOST EXCELLENT MAJESTY.

May it please your Majesty,-We, the Members of the Royal Institution of Great Britain, respectfully desire to express to your Majesty our grief for the loss which has fallen upon the Kingdom, upon our Institution, and, with exceeding weight, upon your Majesty personally.

May it please God, who grants consolation in His own due time, to give it to your Majesty, even while your thoughts are directed towards him that is gone, and may the recollections of our Prince's doings whilst in life have an abiding influence for good upon the many millions who have heard of and rejoiced in his name.

CHEMICAL SOCIETY.

Thursday, January 16, 1862.

A Paper, by Dr. H. BENCE JONES," On the Simultaneous Variations of Hippuric and Uric Acids in Healthy Human Urine," was read by the Secretary.

The determinations of the amount of hippuric acid

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Chemical Society.

Sp. gr. of
Acid.

Weight of Salt.

CHEMICAL NEWS, Jan. 25, 1862.

Result of Evanoration.

present in urine that had been made both by Dr. A. Wise-centrate 1, sulphate of lead is deposited. With nitric acid man and by M. Ravenshoe, gave very high results; the the following quantities were dissolved :method employed by M. Ravenshoe being that recommended by Profesor Liebig, two healthy men being the subjects experimented upon; the amount of hippuric acid in the urine obtained from patients suffering from different diseases had also been determined, but Dr. Bence Jones thought that further experiments on its occurrence during disease were needed.

A table was exhibited showing the amounts of uric and hippuric acids occurring in samples of urine obtained from various subjects both before and after food had been taken, control determinations having been made in each case; Liebig's method being employed.

Dr. MARCET remarked, that he had tried to extract hippuric acid from urine by means of ether, but that other acids and urea were partially taken up by the solvent, and also the colouring matter of the urine; it was, however, easier to obtain it from other parts of the system, as for instance from the blood; he had found the following process to answer in this case:- After coagulating the blood by heat, filter, and concentrate, then add alcohol, filter, again concentrate, add dilute sulphuric acid to separate fat, neutralise with chalk, evaporate to dryness, and extract the hippurate of lime by means of alcohol. He also stated that the presence of this acid in diseased urine had been detected by several experimenters.

Mr. BLOXAM said he had employed several published methods for the extraction of hippuric acid, but had not found them to succeed satisfactorily.

The PRESIDENT said that Dr. Bence Jones had employed Liebig's process, which was to evaporate the urine and add hydrochloric acid, and then to act on the precipitate obtained with ether, so that the urea did not interfere; that the concordance between the control determinations was a proof of their correctness, and that he himself was assistant to Liebig when he was making experiments upon this method of determining the acid, so that he could speak from experience as to its correctness.

"On the The next Paper was by G. F. RODWELL, Esq. Solubility of Sulphate of Lead in Hydrochloric and Nitric Acids." In order to determine the solubility of the salt in acids of different strengths, pure and dry sulphate of lead was digested in the acid at the ordinary temperature for a period of from one to ten days; the maximum amount was, however, always dissolved before the fifth day. To determine the amount dissolved, a portion of the solution was weighed out, a little sulphuric acid added, and the whole evaporated to dryness, ignited, and weighed. It was impossible to evaporate in the ordinary way a concentrated solution of the sulphate in hydrochloric acid, for a scum was apt to form on the surface, and this was thrown out by the expansion of the steam underneath; this difficulty was overcome by evaporating the solution in a crucible, and finishing the process in an air bath, the lid being placed on the crucible. The following determinations have been made :-A hundred grains of hydrochloric acid dissolved the following weights of

the salt:

[blocks in formation]

If the solution be evaporated, plates of chloride of lead are deposited, which, when dissolved in water and recrystallised, furnish needles; but if the solution of the salt be evaporated until the sulphuric acid becomes con

1'079

0*329925

1*123

5 755000 0.784000

1'25

1'42

0'009725

Octohedral crystals of nitrate of lead.

A crystalline powder of nitrate of lead.

When the salt was digested with nitric acid containing sixty per cent. of acid, it was almost entirely converted into octohedra of nitrate of lead, but the whole of the sulphate was not decomposed even on standing for several

days.

Dr. GLADSTONE remarked that it was a curious circumstance that diluting a solution of sulphate of lead in hydrochloric acid, chloride of lead was deposited, and he thought a redistribution of the acids and base took place. He had examined solutions of phosphates, oxalates, and other salts, and found that no precipitate was produced on dilution; he had observed that if to a solution of sulphate of lead in hydrochloric acid either sulphuric acid or a lead salt were added, sulphate of lead was deposited.

Mr. FIELD said that sulphate of lead was completely deMr. DE LA RUE remarked that sulphuric acid will not composed either by oxalic or hydrochloric acid. separate lead completely even from a solution of the acetate, and that more remained in solution than was due to the solubility of the sulphate in water.

The next Paper was by Dr. HUGO MULLER, "On a New Mode of Effecting Chlorine Substitutions." He had found that a great difference existed between the action of chlorine alone on organic compounds, and its action on the same compounds in the presence of iodine; also, that in the latter case the action took place with much greater facility. Benzol, for instance, although acted upon with difficulty by chlorine alone, was attacked with ease by the mixture of the two elements; two series of compounds being obtained, the formulæ of which are expressed as follows:

€6 He Cl2 He Cl Є H& Cle

6

6

€ H, Cl H1 Cl2 € Hy Cl

From these tables it will be seen that when chlorine alone was employed, direct union took place, but with chlorine and iodine together substitution products were obtained. Burmese naphtha had also been experimented upon and furnished several compounds. With bisulphide of carbon, chloride of sulphur and chloride of carbon were obtained, and a third body, which was probably a compound of carbon, chlorine, and sulphur. When chlorine was passed into a solution of iodine in acetic acid in the cold, no action took place; but on the application of heat chloracetic acid was produced even in the dark, although when chlorine alone is employed strong sunlight is known to be It was possible that the iodine acted as a necessary. carrier of the chlorine, or that the action might be similar to

that of pentachloride of antimony, or of phosphorus.

The PRESIDENT remarked that the ordinary process for obtaining substitution compounds was sometimes very tedious, and that a process which would render their preparation easier would be very valuable.

Mr. DE LA RUE said that the present results were merely the beginning of a series which Dr. Müller and himself hoped shortly to lay before the Society.

The PRESIDENT inquired how rapidly the action of chloroform upon glacial acetic acid took place, to which Dr. MULLER replied that it acted with great rapidity, the limit of production depending merely on the size of the apparatus.

Mr. BLOXAM inquired whether phosgene gas could be produced in this manner; but it appeared that the ment had not yet been tried.

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