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pose that for a moment. He battles stoutly against what he believes to be error, and I found no fault with that. What I did complain of was the passage which I quoted in my letter of January 10th. Every one to whom I have shown his paper agrees that the words as they stand distinctly imply that I denied the fact of the lecture-table experiment with Glauber's salt.

Prof. Tomlinson denies that he anywhere implied this. I am glad to accept this as an expression of his intention, but I cannot admit it as a fair description of the words he used. I have laid stress on this only because the line taken by Prof. Tomlinson in that paper is that I am at variance with all my predecessors, a point to which I shall have to recur, and that after repeating some of my experiments his results were contradictory of mine.

Prof. Tomlinson also protests against my making him out to be ignorant of the very simple conditions necessary for the success of the experiments with drops on a glass plate. The case stands thus:-In his paper he gives a general statement, applicable apparently to all supersaturated solutions, that when a point was drawn through a drop so as to deform it, crystallisation sets in. This is in dry weather. I have drawn a point through hundreds of drops of the strongest solutions of sodium sulphate, carbonate, and acetate, on recently washed plates, in all kinds of weather, without causing crystallisation; I have just tried this with sixty drops of a strong solution of the acetate, and it was inactive in every case. I have deformed drops of ammonia alum, which had begun to deposit the modified salt, on a plate over calcium chloride, and repeated this with sodium carbonate and acetate over sulphuric acid, and the scratching had no effect whatever when the plates were put back over the chloride and acid. I explain this difference in our results by supposing that Prof. Tomlinson did not take sufficient care in cleaning his plates. There is nothing which need hurt him in the supposition, because it is only the experience given by a long series of experiments with plates which has taught me what precautions have to be taken. It is in the same spirit that Prof. Tomlinson quietly dismisses what he calls my minute criticism, as throwing no light on the circumcumstances under which these solutions crystallise. Experience has taught me that it is only by the minutest possible criticism of each case that we can hope to arrive at the explanation of these very difficult phenomena. I recognise at present three well-established ways in which a supersaturated solution may be made to give the normal salt. The first is by introducing a crystal of the same salt, or of an isomorphous one of similar constitution as Mr. Thomson has recently shown. The second is by the mechanical action of absorbent substances, when not at once saturated by the solution. The third is by cold. Until it is proved that these three do not apply to the case in point, I refuse to look for any other cause.

Now the first two of these causes exhibit the most extraordinary delicacy in their mode of operation. Mr. Liversidge agrees with me in explaining the action of the minute aërial nuclei by their absorptive power. Hence if Prof. Tomlinson's plates had minute organic particles on them in dry weather these would cause the crystallisation of his drops when, by deforming them, he brought the solution in contact with these nuclei. He notices himself that if the tail formed sprang back crystallisation did not ensue, and I have always found that plates exposed to air are much more likely to be active than plates recently washed or dried under cover.

The extraordinary delicacy of the second cause has been proved in the course of my own experiments, of which I will give a few. A large glass plate, on which drops of sodium acetate had been made to crystallise, was carefully washed in cold water, and then dried and exposed to the air. A great many drops of a strong solution of the acetate were then put on it, and all remained liquid; but I found that scratching with a pin inside the drops made every one of them crystallise instantly, although the in was washed in boiling water or heated red-hot after

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CHEMICAL NEWS,
April 4, 1879.

every experiment. I naturally thought at first it was a case of scratching causing crystallisation; but I had so often scratched the acetate without effect that I was very loth to believe it. I then washed the plate with boiling water, and then scratching had no effect whatever on many drops of the same solution. The acetate has a very remarkable power of adhesion, and was still present in the depressions of the plate covered by weaker solution, but was unable to determine the crystallisation of the drops until scratching brought it in contact with the strong solution.

A few days ago I tcok an apparently clean plate, washed it carefully in cold water, put drops of the acetate on it, and then put it over calcium chloride. In an hour or two the modified salt was forming on the drops by evaporation; then scratching with a pin made every drop crystallise. This looked very like a confirmation of Prof. Tomlinson's results. But on washing the plate in hot water, and repeating the experiment, scratching had no effect whatever, and when put back over sulphuric acid for two days only the modified salt was formed. Probably the plate had previously been used for the acetate; possibly, in the first case, nuclei had not been thoroughly removed, but the acetate is so little sensible of absorbents that this latter supposition is not at all probable.

Again, a pin had been frequently used for making the acetate crystallise, and often heated red hot; it was rubbed through the fingers and then left 3 hours in cold water; it was then immediately active, not on quietly putting it into a drop, but on scratching; whilst boiling water cleaned it at once.

It is evident that these facts must be taken into consideration if we do not wish to have results ascribed to all sorts of wrong causes. Another fact of the same kind is not without interest. Dr. De Coppet has described two isomeric modifications of anhydrous sodium sulphate (Comptes Rendus, lxxviii., p. 194), one formed by dehydration above 33, the other formed at lower temperatures. This latter kind, he says, determines the crystallisation of a solution of the salt as the normal, whilst the former does not. M. Gernez suggested that this was because at a low temperature the sulphate did not perfectly effloresce. I tested the point by rubbing some of the salt very fine in an agate mortar and then exposing it for weeks over calcium chloride. I then took a plate with a large number of drops of the sulphate and tested various portions by taking up a little with a pin and introducing it into a drop. I found that all the thicker parts were immediately active, but that here and there a small very thin patch was inactive, and the anhydrous could be seen to dissolve in the drop. Hence it is clear that M. Gernez's explanation is correct. This method of testing is one of extreme delicacy for the presence of salts which form supersaturated

solutions.

Another illustration of the necessity of minute investigation is the following:

Some years ago I showed that scratching a solution of sodium sulphate in about six parts of sulphuric acid causes crystallisation. I attributed it at the time to vibration upsetting the state of unstable equilibrium. My colleague, Dr. Tilden, found that the same thing happened when drops of potash alum were scratched; and at a lecture in Bristol he gave it as another instance of vibration. But I have since found that by taking extreme care in cleaning the plate and using one recently washed scratching is by no means always active. I attribute this case also to the presence of absorbents on the plate. I am also strongly inclined to believe that the effect of scratching the acid solution mentioned above is due to the same cause. Rubbing drops of this with a hard, compact wood has no effect, but it always crystallises by absorption on the end of a match simply dipped in the drop and laid aside. Little shavings of a match kept floating on a drop act in the same way, but very often not if they are pushed into the drops. It is easy to see how the solution would gradually act on the organic particles

in the depressions of the plate, and then scratching brings | the conditions under which the crystals were formed is the crystals which are forming into contact with the interesting to geologists as well as chemists. stronger solution. I did once find a plate inactive when scratched, but I have never been able to reproduce the conditions, although I have tried several ways of cleaning the plates. It must also be carefully borne in mind with regard to these experiments with drops that the sensitiveness to absorbents depends on the strength of the solution, and also on the temperature.

In hot weather 1 found that a rather weak supersaturated solution of sodium sulphate was absorbed by filterpaper without giving the normal salt even when dry, as the filter-paper was cut up and introduced into drops with out producing any effect. This can never be done, as far as my own experiments go, with strong solutions of that salt. Absorbents also, such as filter-paper, have no effect | whatever on sodium acetate except in the very strongest solutions.

It appears, then, that in discussing the question why these solutions crystallise or do not crystallise in a given case, we have to take account of the strength of the solution, of the temperature, of the possible presence of the salt when least expected, of the freedom of the plate from dry absorbent bodies derived from the air or elsewhere, and of a specific sensitiveness to absorbents peculiar to such kind of salt. This necessitates minute criticism, and with all deference to Prof. Tomlinson's opinion, I maintain that one or other of these considerations has frequently led me to a simple explanation of results which are otherwise most puzzling. The action of oil on these solutions is a very simple one according to Prof. Tomlinson; when a film adheres to the solution the normal salt separates. But I find that the phenomena are much more complicated.

When solution of sodium carbonate is dropped into oil, or is rubbed with oil, a salt separates at once, which is not the normal salt, as it can be introduced into drops without causing crystallisation. I have also seen a very pretty thin flexible opalescent film form at once round the sides of a drop of ammonia alum on oil. As I write, three drops of a strong solution of potash alum are lying unaltered in castor oil; yet I have often found oil rubbed on a plate powerfully unclear to this solution. On sodium acetate I have never found oil have any effect, nor on the sulphate when proper precautions are taken. It is quite possible that the oil acts by catching up absorbent particles of dust, but the subject needs investigation.

I have omitted to notice a property possessed by these solutions which may easily prove a source of error. When small well-shaped crystals of the salt are forming in a solution or in a drop they may continue to grow for hours very slowly; but if one of these is broken the drop crystallises with a flash. It may, as far as my experiments go, be taken as a general law that broken crystals have much more effect in producing crystallisation than perfectly-shaped ones. The crystal seems to have the power of growing with much greater rapidity along one of its axes than along the others. It is this property which makes a strong solution crystallise in fibres, while a weak solution gives well-shaped crystals. In the former case the growth of the more powerful axis does not sufficiently diminish the strength of the solution in front of it to check the rate of growth; in the latter case the crystal is surrounded constantly by impoverished solution, which gives time to the lateral forces to develop themselves.

Hence a drop on a plate may really be crystallising in thedepressions of the plate, but very slowly, and the experimenter will find that scratching causes crystallisation at once, or that the drop will crystallise spontaneously

after a certain time.

I find that a pin which has been heated red-hot often, and is used for making the acetate crystallise, and is then left in water for an hour or two, makes drops of the acetate crystallise very slowly in large well formed crystals, whilst scratching makes it crystallise at once in fibres all oyer. This subject of the relation of crystalline form to

The last point I have to notice is one which Prof Tomlinson insists upon in his paper, and in his note to you; it is that I am at variance with all my predecessors. He says that Loewel, Violette, and Liversidge expressly state that porous bodies, bodies greedy of water and capable of hydration, are incapable of determining the solidification of these solutions."

He has forgotten, as I did at the time of making my. experiments on absorption, that Mr. Liversidge, in his last paper in August, 1870, enunciated the absorption theory in these words:—

(1) It is not impossible that nuclei consist of microscopic organisms which act by abstracting water, the action being set up at a point from which it is propagated throughout the mass; (2) that they are rendered inactive by heat because it entirely destroys them; (3) that their action is arrested by previous saturation in water, because they then can no longer abstract water from a saline solution."

He had only made a couple of experiments with lycopodium, which he found to be active when dry and inactive when wet, but he expressed a hope to have shortly the results of other experiments. Unfortunately, : he never resumed the subject. My own experiments on absorption were begun five years later, when I had forgotten all about Mr. Liversidge's suggestion, and when I was working at a different part of the subject. They entirely confirm Mr. Liversidge's views as to the action of nuclei; they show that the action of absorbents in considerable quantity resembles that of nuclei, but with two important modifications, which determine the conditions under which the absorbents act-namely, that they are inactive if saturated at once by the solution, and that very rapid absorption often prevents crystallisation. It is only in virtue of this extension and modification that I can lay any claim to the theory as my own, and my results are in perfect harmony with those of the only person who, with the exception of Prof. Tomlinson and M. Gernez, has really worked at this subject in recent years. It is true that Loewel, Violette, and Liversidge state that phosphoric anhydride and other dehydrating substances have no effect; but I have shown that when these substances are introduced into a considerable bulk of the solution, so as to be saturated at once, crystallisation does not ensue.

ON INDIGO-BLUE
FROM

POLYGONUM TINCTORIUM AND OTHER
PLANTS.

By EDWARD SCHUNCK, Ph.D., F.R.S.
(Concluded from p. 130).

Bletia Tankervilliæ.

THE Occurrence of a blue colouring-matter in this and other plants belonging to the Orchidaceae, such as Calanthe veratrifolia, was first noticed by Clamor-Marquart and by the late Dr. Crace Calvert+. The attention of these observers was directed to these plants by seeing the blue colouration appearing in the white petals of the flowers on their beginning to fade; and they found the blue colour to be due to indigo. In accordance with the views then prevailing, they assumed the pre-existence of the colouring-matter, either as indigo-blue or as its hydride, in the tissues of these plants. It is easy to see, however, on reading the accounts of their experiments that the colouring-matter was really formed during the processes

*Buchner, Repertorium f. die Pharmacie, B. lvii. S. i. + Journal de Pharmacie, t. vi, p. 193.

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employed for its extraction; and it seemed to me, therefore, highly probable that the plant would be found to contain some glucoside similar to indican.

Bletia Tankervilliæ is not difficult to procure, being frequently grown for the sake of its handsome brown and white flowers and its general beauty. The leaves of the plant having been cut in pieces and ground with water between two stones to a pulp, which is strained through calico, yield a green muddy liquid which, heated to near the boiling-point, gives a thick green coagulum. The liquid filtered from this coagulum is clear, of a deep yellow colour, with a slight acid reaction and an acrid taste. When this liquid is mixed with sulphuric or hydrochloric acid and left to stand, it deposits dark-coloured flocks consisting of indigo-blue mixed with a substance which imparts a purple colour to boiling alcohol, probable indi. rubine. The presence of glucose may be detected in the filtrate by the usual test, while the same test applied before the addition of acid shows no indication of its presence. It may hence be inferred that the liquid contains in solution a glucoside similar to, if not identical with, indican. It undergoes, like indican, a complete change when submitted to the action of alkalies; for if its watery solution be mixed with caustic alkali and boiled, then with an excess of sulphuric acid and again boiled, it deposits brown flakes, which are found to contain but little indigo-blue, while in the filtrate only a trace of glucose can be detected. The same change takes place gradually when the watery solution is left to stand for several days at the ordinary temperature.

The gradual formation of indigo-blue in the leaves of Bletia Tankervilliæ may be easily traced in the same way as with those of Polygonum tinctorium, by placing the lower ends, immediately after cutting, in dilute hydrochloric acid and leaving them freely exposed for a few days. The acid, as it ascends, causes a dark discolouration; and the part discoloured, aiter immersion in boiling alcohol to remove the chlorophyll, appears blue.

Indigofera tinctoria.

It would be a matter of some interest to ascertain in what state the colouring-matter exists in this the most important of all the plants yielding indigo. From what I have said, however, it will be apparent that, in order to arrive at a certain conclusion, it would be necessary to work with fresh leaves; for if they contain a glucoside resembling indican, this would in a very short time undergo complete decomposition. I obtained some seeds of Indigofera tinctoria from Messrs. Vilmorin, Andrieaux, and Co., and treated them in accordance with the directions they kindly gave me. The seeds germinated, and the young plants lived for some time in a hothouse; but unfortunately, they attained no great size, and soon decayed and died, so that I was unable to obtain a quantity of leaves sufficient for examination.

Mr. P. Michéa, an intelligent indigo-planter, with whom I have been in correspondence, gives me, however, some interesting information relating to this part of the subject. Mr. Michéa writes to me as follows:-"It was my finding in the Indigofera of India (in the wild plant which grows at many places in the three Presidencies as well as in the cultivated species of Bengal, the North West, and Madras) a glucoside substance perfectly similar to the indican of the Isatis tinctoria in all its properties, which made me declare that the colouring-matter of the Indian Indigofera was due to indican."

The experiments just described lead to the conclusion that in all the indigo-yielding plants hitherto examined, the colouring-matter is derived from a glucoside which splits up with great ease into indigo-blue and glucose, and that this glucoside is probably, in all cases, the same, and identical with, the indican of Isatis tinctoria.

Various other plants have been supposed to yield indigoblue. Of these I have examined the following:Galega officinalis.

Hedysarum Onobrychis (Sainfoin).

CHEMICAL NEWS, April 4, 1897.

Polygonum Fagopyrum (Buckwheat).

Polygonum Persicaria.
Rhinanthus Crista-galli.

Sophora japonica.

Spilanthes oleracea.

The leaves of these plants, when treated in the manner bling indican, and showed no indications of containing any above described, yielded no trace of any substance resemblue colouring-matter like indigo.

CRYSTALLISATION OF PHOSPHORUS.

By GEORGE WHEWELL, F.I.C., F.C.S.

IN 1872, while experimenting on the action of phosphorus on nitrogen gas in sealed tubes, after melting the phos. phorus and spreading it over the sides of the tube and allowing the tube to stand for several weeks, I noticed small colourless crystals begin to form. In 1874 I noticed abstracts of two papers in the Chemical Society's Journal (2nd series, vol. xii., p. 869) by J. L. Smith and W. L. Herman, on the formation of crystals of phosphorus in vacuo. I wrote a note to the CHEMICAL NEWS (vol. xxx., p. 168). I did not claim priority or originality, or try in any way to detract from the merit of Messrs. Smith and Herman's papers. In Mr. Herman's letter (vol. xxx., P. 194) he tried to throw ridicule on my note, and even hinted his opinion that I had not made any crystals at all. I prepared a test-tube and sent it to Dr. Burghardt, of the Owens College, Manchester, and I append his letter, as requested by Mr. G. E. Davis (vol. xxxix., p. 115). "The Owens College, Manchester, "March 2, 1875.

66

"DEAR SIR,

I thoroughly investigated the matter you requested me to enquire into, immediately after receiving the tube containing the phosphorus crystals. Of course you are aware that crystals of phosphorus have been ob tained in other ways long ago, and it was conclusively proved that they belonged to the regular system of crystallography. The crystals in the test-tube you kindly sent me were undoubted phosphorus crystals, exhibiting the two characteristic forms observed on crystals prepared by dissolving phosphorus in rock-oil when hot and cooling, and the methods published long ago. The forms I cbserved were the regular octahedron and the rhombic dodecahedron, with rather rounded edges, the interfacial angles not being sufficiently well defined to allow of accurate measurements being made. There can, however, be no doubt about their being the two forms mentioned above. On opening the tube for a few seconds fumes of phosphorus came out, and the tube on being closed again, and left alone for a few days, was thickly coated with amorphous phosphorus and the crystals had vanished. -Believe me, &c.,

"Dear Sir,

"C. H. BURGHARDT." "The Owens College, Manchester, "March 18, 1879.

. . . The forms observed on the crystals were the octohedron and the rhombic dodecahedron, the former predominating; the crystals did not exhibit any sharply. defined edges or angles, consequently goniometrical measurements were not possible. The crystals were perfectly transparent. -With kind regards, &c.,

"C. H. BURGHARDT." My friend, Mr. W. H. Wood, now of the Yorkshire College, wrote me, in November, 1874:

I have tried your method of producing phosphorus crystals and was successful, as I could easily distinguish crystals when I examined the tube two or three days

after.

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Very few chemists have made crystals of phosphorus, and the only thing I claim in the above method is a very

CHEMICAL NEWS,
April 4, 1879.

ready means of preparing crystals of phosphorus suitable for lectures or showing it to a class when treating of phosphorus and its compounds. The method places phosphorus crystals in the hands of anyone who cares to spend ten or fifteen minutes in preparing them. I am sorry I have not studied the subject further, being fresh from College at the time, and the note being my first attempt at writing I was somewhat cowed. I came to the conclusion that Mr. Herman thought he had a vested right in crystals of phosphorus.

In every kind of spectroscopic observation, high or low, of fire or flame, public or private, brilliantness in the light operated on-so far as it can be fairly commanded-is the soul of success. In private researches, too, more particularly, where we merely look into the eye-piece of a small optic tube for our own sole and, for the time, solitary satisfaction, the mere quantity of shining matter being examined is of no sort of consequence; for we view of it at a time only as much as fills a little slit in a metal plate about inch high and inch broad. A minute, or no I have found the following the best plan for producing more than microscopic sized, particle is therefore enough, the crystals:-Take a piece of glass tubing and seal one in that way; but brilliant, and even three times brilliant, end (or a test-tube); place at the bottom of the tube a the intrinsic light of that little particle must be, or you piece of phosphorus about the size of two peas; draw out will be condemned to employ only the least dispersive of the other end; then heat the tube, commencing about one prisms wherewith to form its spectrum; and therein, inch or so above the phosphorus, so as to drive out as from the extreme red, all the way through the orange, much air as possible; then seal the open end (or cork the yellow, green, blue, and right up to the ultimate violet test-tube and make it air-tight). Melt the phosphorus, and and lavender grey of the spectral field, you will fail (if spread it as thinly and evenly over the sides of the tube | your spectrum is of the all important discontinuous" as possible. Allow to stand for a week or two, or place order) to see anything but merely a few faint, hazy-edged, into a freezing mixture, when crystals will form in a few unsatisfactory bands. In place it might, or should, have days. been of multitudes of vivid lines, capable of almost unlimited nicety of micrometric measurement, and as firmly fixed in their several and respective spectrum places, as are the very stars of heaven in their almost eternal positions.

END-ON ILLUMINATION IN PRIVATE
SPECTROSCOPY,

AND ITS

APPLICATIONS TO BOTH BLOWPIPE FLAMES
AND ELECTRIC ILLUMINED

GAS-VACUUM TUBES.*

By PIAZZI SMYTH,

"Then, of course," you will say, "every sensible spectroscopist, whenever at least he is observing in a chamber upon any chemical element within his grasp, endeavours to make the illumination, or incandescence under which he looks at that particular matter, as bright as he possibly can."

Astronomer Royal for Scotland, and past President of R.S.S, Arts. glories in doing; for he finds that he cannot make the

PART I.

Defects of Former Methods, and New Conditions to be
Fulfilled.

As there is nothing in the shape of splendid optical pro-
jection of grand phenomena on a large screen connected
with the present paper, and as it refers merely to a prac-
tical difficulty, as met with by a private worker in a small
way, in connection, too, with only a very limited branch
of the general subject of spectroscopy, some apology may
be necessary for bringing so apparently trifling a matter
before any public meeting. Especially, too, is such an
explanation required before this long-established Society,
which has had all the finer bearings of the higher spectrum
analysis expounded to its members so often and so
eloquently by Dr. Stevenson Macadam, and illustrated so
glowingly by Mr. Hart's electric lamp, years and years ago,
that not a few persons may have almost identified the
subject itself, or anything about spectroscopy, with that
particular and assuredly most magnificent method of
demonstration. My excuse, therefore, can only consist
in trying to make out, and perchance bringing home,
though by mere words only, to the inner conscience of
some real workers (of whom there must be many here)
the exact manner of occurrence of a serious, albeit small,
case of positive scientific difficulty; or in showing how a
very lion of a trouble was one day found to be seated
right across the special path of progress and research
which I was desirous of pursuing. But how, after due
interrogation as to wherefore he came to be there, the said
lion was presently induced to get up, make himself scarce,
and not exhibit his threatening front, to me at least, in
that locality again.

If, therefore, the Society will be graciously content with such a modest bill of quiet fare as that, I will at all events endeavour to make the nature of the case very clear. With this purpose, therefore, I now commence with what is generally admitted by all the world as being foundational in spectroscopy; while it is also the necessary beginning of our subject for this evening, viz.:

* Read before the Royal Scottish Society of Arts, February 10, 1879.

Most certainly! That is exactly what he does, and even said stuff too bright for the spectroscope, if only he preserves it at the same temperature. But precisely there comes in our envious and opposing lion; for almost every known attempt of man as yet to increase the brightness of a light, when at all successful in that respect, is found in the end to have enhanced its temperature amazingly. And if the temperature be so enhanced, where is the man who shall venture to predict, from theory alone, what the result will be in that potentially, most extensive, almost interminably long region of accurately measurable facts, the prismatic spectrum of light; wherein red is from violet, as far as north is from south?

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Do you doubt there can arise any real and serious spectral changes from merely altering the temperature of one and the same flame of burning matter? Look at the metal lithium in any of its salts. How early in the history of spectroscopy did not that too little appreciated genius Fox Talbot show that chloride of lithium in a lamp flame formed one brilliant line in the scarlet-red and another very faint one in the orange-brown of the spectrum. Wherefore the brighter of them was called lithium a, the paler lithium ß; and the innocent, trusting public thought they would always know where, in the spectrum, by those letters as names, to find those lines.

But after the subsequent grand outcome of the full spectrum analysis of Professors Bunsen and Kirchoff, and when not a few men insisted on rising from the mere beginnings of heating by flame, up to the ecstatic increase of temperature by the electric spark,-behold the lithium's red line, though still in exactly the same part of the spectrum's measured scale as before, has become woefully pale; the lithium orange line has burned up like a beacon; and far, far away in the comparatively distant regions of the spectral blue, there is a new line of almost rivalling brightness. Wherefore a new naming of the lines by Greek letters takes place among spark observers; the identical lithium ß of flame-spectroscopy becoming lithium a of electric spark spectroscopy; a line hitherto unknown becoming lithium y; and poor old lithium a being known now only as lithium 6.

But even that is not the end of the changes of brightness and name with increas of temperature; for pres

146

Chemical Society.-Anniversary Meeting.

ently still more ambitious geniuses increase the power of, their galvanic batteries, the size of their induction coils, the length of their sparks, and then condense them both in time and space with Leyden-jar apparatus until the heat is something so fearful that, in the spectrum of one and the same lithium salt, it is no longer the red, nor the orange, nor even the blue line you care for now; but further away in more distant spectral regions there burns a violet line; and beyond, yes, vastly further beyond that still, there arise exquisite lines in the ultra lavender and even grey wilds of spectral space. So then, to suit these altered brightnesses in the hotter condensed-spark spectrum, a new and yet more altered application of Greek letters, as names, takes place; and being attended to in their Memoirs by some persons, though not by others, will contribute to the future scientific confusion of many; and all on account of a mere change of temperature in a lithium light.

Or hear those first-class German observers MM. Plucker and Hittorf, at page 6 of the Philosophical Transactions for 1865, as to what still more extensive and positively wholesale and radical spectral changes, mere altered degrees of heat may work. "The first fact," say they, "which we discovered in operating with our tubes, guided by the above-explained principles, was the following one:-There is a certain number of elementary substances which, when differently heated, furnish two kinds of spectra of quite a different character, not having any line or band in common." So that if you have learned to recognise every line in the spectrum of, say, nitrogen at one temperature, it will not be by ary of those lines, but by some perfectly different and unlikely-looking ones, that the element will manifest, or for a while conceal, itself at another temperature !

Neither does the application of a higher heat always brighten and improve a spectrum, as witness the element cæsium, discovered by Professor Bunsen through means of the old flame spectrum analysis. What a refined and exquisite spectrum, too, does not cæsium present in the lamp flame! So many lines it has, and all of them thin, sharp, classical almost in the orange, yellow, green; and then two gorgeous ones in the blue, but both of them so clearly defined, so admirably distinct, that I, in my small way, should have long ago established cæsium as my prime standard reference in all lamp spectroscopy, if it gad not been so dreadfully expensive.

Yet what becomes of this most valuable, almost invaluable, element cæsium when promoted from mere flame to the higher temperature of the condensed electric spark? Alack! there is only then to be seen one faint solitary line, which has nothing in common with its departed brethren, and but little beauty of its own. With such a spectral calamity befalling poor cæsium, I have been watchfully careful, in any attempted increase of the brilliancy of other spectra, to interfere as little as possible with their temperatures. And it is simply because I have recently proved the practical efficiency of a very easy method of accomplishing at least a considerable amount of brightening up, without any increase of heat whatever, in both flame and spark spectroscopy, that I have ventured now to lay the said method for merely what it may be worth, and to what extent it may be new, before the Royal Scottish Society of Arts.

(To be continued).

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{CHEMICAL NEWS,

April 1879.

much ground for congratulation, the past year having been one of quiet prosperity. Various alterations have been made in the bye-laws, and the publication of the Society's Journal has been improved. 61 Fellows have been elected, and 18 have died, withdrawn, &c., during the past year, the present number of Fellows being 981. There are 34 Foreign Members and I Associate; 28 names are awaiting election. The Treasurer's report shows an increase of receipts over expenditure to the amount of £1964 9s. 5d. (including a legacy of £1000 from the late Mr. Sidney Ellis). 68 papers have been read before the Society during the past year. Lectures have been given by H. C. Sorby and S. H. Vines. The number of papers from 1859 to 1869 averaged 36 annually, fell as low as 22 in 1872, and since has rapidly increased. There is an increasing disposition to illustrate papers by experiments: this practice adds much to the interest of the meetings of the Society. On the 13th of November last Prof. Würtz delivered the Faraday Lecture at the Royal Institution, "Sur la Constitution de la Matière à l'etat Gazeux." Those who were present will not readily forget the perfect lucidity, the rare manipulative skill, or the enthusiasm of the Lecturer on that occasion. The Council have carefully considered the condition of the Library and its rules. It has been resolved that no serial publication of which the Society does not possess a duplicate copy shall be taken away from the rooms. Duplicate copies of back numbers of Liebig's Annalen and the Annales de Chimie et de Physique have been ordered, and these works, together with other important serial publications, are now being taken in in duplicate. Many new books have also been ordered, and on this point the Council would be glad of suggestions from Fellows of the Society. Arrangements have been made for Fellows at a distance to have books sent to them on giving a written order and paying the cost of carriage. A new series of instructions has been drawn up for the use of abstractors. Great efforts have been made to publish the Journal within the first week of each month. The ventilation of the meeting-room has been much improved by the combined investigations of Mr. Perkin and Dr. Russell, and alterations suggested by them. A new plan of choosing the President has been adopted this year. As the Faraday Lecture occurs only once every three years, whilst the President is elected for two years, it was suggested that it would be better to elect some Fellow who has already filled the office of President for one year, so that the Faraday Lecture would occur in the second year of the next President's tenure of office. A separate Report of the Research Fund is submitted, the President suggesting that a portion might, with peculiar fitness, be devoted to the accurate determination of che. mical constants. A short biography of each of the Fellows deceased was then read, viz., of M. Malaguti (Foreign Member) Messrs. W. Baker, A. Bird, W. A. Lyttle, W. A. Stewart, and J. Wiggin. The President concluded his address as follows:-" While there is much to encourage us in the progress of the past twelve months, I think I only express the general feeling when I say that we ought not to feel satisfied with present attainments. The Society exists" for the general advancement of Chemical Science;" this means both the encouragement of research and the diffusion of the knowledge of new discoveries. With regard to the promotion of research, as our members now exceed Icoo, and the laboratories of our land are growing in importance, we may surely look for a larger amount of original work in coming years: we should also seck, not only to add to previous knowledge, but to increase what I may venture to term the scientific culture of the workers. In our laboratories we are isolated, and are apt to look upon our own pet subject as of prime importance; but when we meet in these rooms, or turn over the pages of our Journal, we are carried away to many different fields of thought in succession. This promotes largeness of view, and must react favourably upon the cultivation of our individual corner of the great field. I trust that our Society will never devote its energies too exclusively to

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