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Presence of Arsenic in the Vapours of Bone Manure. (Ct. 13, 1576.
were only known in the anhydrous state. Now, I do pretend to have discovered the facts, whatever their importance may be, (1) that all crystalloid bodies soluble in water are capable, at temperatures below o° C., of uniting with water to form solids containing definite quantities of water; (2) that the temperatures of solidification of these bodies, which I call cryohydrates, determine the limiting temperatures of freezing mixtures.
"With regard to the second part of your reporter's remark, namely, the accusation of sensationalism, I am constrained to say that it is as discourteous as it is unfounded, and I shall be glad to learn that, on reflection, your reporter regrets having allowed an expression of such questionable taste to have escaped him.
Prof. Guthrie admits that he does not pretend to be the discoverer of water of crystallisation as it is ordinarily understood.' Well, but this 'water of crystallisation as it is ordinarily understood' is solid water, and we were therefore quite correct in maintaining there was nothing new in this. We never said that Prof. Guthrie had not discovered various salts which could, under certain circumstances, be got to crystallise with water, but we only found fault with the designation, which includes much more than Prof. Guthrie himself claims to have achieved. Surely the giving of such a designation justifies the charge of sensationalism."
"September 30, 1876.
"The remarks appended in the Athenæum of the 30th inst. to my note on your report of my communication to the British Association on Solid Water,' call for a word or two. You say:
*** Well, but this water of crystallisation as it is ordinarily understood,' is solid water, and we were therefore quite correct in maintaining there was nothing new in this.'
"In what? That water of crystallisation as it is ordinarily understood is solid? Of course it is. I never dreamt of denying it. What I asserted, and conceive to be new, is that water may be solid and associated in definite proportions with salts, and yet not be water of crystallisation as it is ordinarily understood. It may either be such water or it may be the water of the cryohy: drates. I used the term 'solid water' to include and because it includes both; and in my communication I spoke of both to discriminate between them. Can you suggest a more appropriate or less 'sensational' expres
"The charge of sensationalism, which I regret to see not only not withdrawn but reiterated, may sometimes be permissible when brought against a writer of fiction; but to bring it on no better grounds than those adduced, against a writer on a scientific subject is injurious and unjust. You owe me an apology.
Athenæum in matters of fact, and I have resented the silly little insult which it has presumed to put upon the members of the British Association. I may add that I do "seriously" think it is the "concern" of a critic who takes exception to an expression, not only to point out how the expression is bad-if he can-but also to suggest a better one-if he can. The first of these duties the Athenæum has attempted and signally failed to perform. The second it declines to attempt because, forsooth, it is
not its "concern."
From the assertion that the difference between the reporter or editor or whoever he is of the Athenæum and myself is only one of taste I must beg to dissent; or only agree to so far as I must admit that the misrepresentation of facts exhibits the worst possible taste.
Although, of course, one has to be serious in remonstrating with a journal devoted to "English and Foreign Literature, Science, the Fine Arts, Music, and the Drama," there is something exquisitely ridiculous in the notion of "Solid Water" being a "sensational" expression. Hard Water" I presume is "Indelicate;" "Cold Water" is clearly "Atheistic ;" and "Vapour of Water" should be avoided on high Esthetic principles if we wish to avoid the imputation of "Cannibalism."—I am, &c., FREDERICK GUTHRIE.
To the Editor of the Chemical News. before writing to you, he would not, I am sure, have SIR,-Had Mr. Wanklyn paused to make a few enquiries have found that at the time the Analyst published the dragged my name into this discussion, because he would article and report which originally gave him offence, I was enjoying a ramble in Switzerland, and I can safely say In fact Mr. Wanklyn and myself have precisely the same never wasting a thought either on butter or Mr. Dittmar. amount of responsibility for the contents of the Analyst for September, viz., that we were both members of the Committee of Publication, and that we each of us neglected and therefore we ought to be the last to throw stones at our obligations as such, and stayed away from the meeting, those who did their duty by attending.
My position as one of the "registered proprietors " of
South London Central Public Laboratory,
"** We must decline to continue this controversy. There seems to be no difference as to facts between Prof. Guthrie and ourselves. We neither denied Prof. Guthrie ON the merit, if there be any, of having discovered the formation of solid water under particular circumstances, nor, as far as we are aware, have we imputed to him any desire of denying the existence of hydrates known before his researches. As to our suggesting a more appropriate designation for the class of bodies discovered by himdoes Prof. Guthrie seriously believe this to be our concern? With regard to the title chosen by Prof. Guthrie for his paper at Glasgow, we have only to say that this is not a question of fact but of taste, and that upon it we shall continue to differ from Prof. Guthrie."
With a journal which, after transgressing in this manner, refuses to apologise when invited to do so I can, of course, hold no further communication. But your readers may permit me to state that there is no "controversy" in the case. I have endeavoured to inform the
THE PRESENCE OF ARSENIC IN THE
To the Editor of the Chemical News. SIR,The pamphlet published by Dr. Adams on the above subject has occasioned some discussion in the CHEMICAL NEWS, and in your number of September 22nd, there is a note which seems to suggest a doubt whether the chemists who made experiments for Dr. Adams had previously satisfied themselves of the purity of their reagents. I may state that I was expected to give evidence in the particular case referred to in the pamphlet, and that I not only made "blank experiments" when originally consulted by Dr. Adams, but made them again in his presence when he came to my laboratory to see the experiments repeated.
Considering the abundant evidence adduced by Dr. Adams, I think it may reasonably be conceded that
Chemical Notices from Foreign Sources.
arsenical vapours are given off during the action of CHEMICAL NOTICES FROM
88, Hope Street, Glasgow.
ALEX. T. MACHATTIE.
[We have also received a long communication on this subject from Dr. Adams, and a further letter from Dr. Milne stating that blank experiments were made. This fact should, in our opinion, have been stated more explicitly in the book. We can devote no more space to the subject, it being contrary to our custom to insert letters referring to our reviews of books, unless, indeed, they point out a manifest injustice to the author, and this we do not admit to have been the case in the present instance.-Ed. C.N.]
IMPROVED FORM OF ASPIRATOR.
To the Editor of the Chemical News. SIR,-In the CHEMICAL NEWs (vol. xxxiv., p. 141) Mr. Richards describes an "Improved Form of Aspirator." This is somewhat similar in principle to one I constructed about four months ago, the chief difference being that Mr. Richards's pump requires a water pressure of 20 pounds to the square inch to exhaust " to within 1 m.m. of the tension of aqueous vapour," while mine takes less than 5 pounds only to produce a vacuum (less, of course, by the tension of aqueous vapour.) I append a drawing of my
The principle involved was fully discussed and illustrated in a paper to the Engineer of June 9, 1876, by Mr. James Brownlee.-I am, &c.
Rugby, October 2, 1876.
A. PERCY SMITH.
NOTE.-All degrees of temperature are Centigrade, unless otherwise expressed.
Comptes Rendus Hebdomadaires des Seances, de l'Acadenie des Sciences. No. 12, September 18, 1876. Lighting by means of Products Extracted from Resinous Trees.-M. A. Guillemare.-The author remarks that if an attempt is made to burn in a common lamp, adapted for oil of colza or petroleum, either oil of turpentine, "essentia viva," or the oil known as pyrogene (the two latter being extracted from resin by fractional distillation over 4 per cent of quicklime), two difficulties are met with which have hitherto proved insurmountable. The resinous liquids of commerce only rise into the wick for a few minutes, after which the capillary action slackens considerably and soon stops. In all the lamps of commerce these same liquids burn imperfectly and diffuse an intense smoke. It is therefore needful to purify them perfectly, aud to contrive a special jet or burner for their use. The clogging of the wick is due to the presence of resin or of naphthalen in solution. These impurities are removed by distillation over an equal volume of water rendered slightly alkaline, a current of steam being passed through the apparatus, and by exposing the oils to the alkaline carbonates. The oils may be regarded as perdirect and prolonged action of concentrated solutions of fectly pure when they are no longer rendered milky by the addition of ammonia. A new burner has been devised, the construction of which is not quite clear, but which is said to prevent the formation of smoke.
Physical Properties of Gallium.-M. Lecoq de baudran.-Inserted in full.
Justus Liebig's Annalen der Chemie,
Investigations on Bodies of the Hydrobenzo and Stilben Series.-T. Zincke.--An introduction to th next paper.
Various Hydrobenzoins, or Stilben Alcohols.-C Forst and T. Zincke.-A very bulky essay, extending 50 pages, and unfit for abstraction.
Apparatus for the more Convenient Determination of Nitrogen. Karl Zulkowsky.-An improved instrument for the determination of nitrogen by the method of Dumas, calculated to be of great value in laboratories where such determinations are frequent. The apparatus cannot be described in an intelligible manner without the aid of the accompanying illustration.
On Ultramarine.—Dr. Carl Bœttinger.—It has always been assumed that the formation of the blue colour of ultramarine depends on the action of oxygen: but in cracked crucibles and on the edges of the blue mass white prolose almost all their sulphur in the form of sulphate. That ducts are often observed, which, on washing with water, this phenomenon is due to oxidation seems to require no further proof. Hence, then, it appears that the colour is destroyed by oxidation. In the author's opinion ideal ultramarine is a compound of silicate of alumina and soda with pentasulphide of sodium.
Communications from the Chemical Laboratory of the University of Moscow.-These communications include a paper by W. Markownikoff on isomeric tartaric acids, and one by the same author on the normal oxyAction of Nitrous Acid upon Acetanilide.-Otto pyro-tartaric acid (glutanic acid), and the isomerism of Fischer. On passing a current of nitrous acid into a re- the pyrocitric acids: an account of the preparation of frigerated solution of acetanilide in acetic acid until the trimethylen-bromide, by J. Lermontoff; on aceton in the liquid becomes green there is obtained, on pouring the urine of diabetic patients, by W. Markownikoff; on cersolution into a large quantity of water, a yellowish pre-tain constitnents of Adonis vernalis, by F. Linderos; and cipitate which possesses the composition and character- a preliminary communication on isomeric dibrom-anthraistics of nitroso-acetanilide.-Moniteur Scientifique.
cen, by Oswald Miller.
Chemical Notices from Foreign Sources.
Les Mondes, Revue Hebdomadaire des Sciences, No. 4, September 28, 1876. Adulteration of Wines.-The author remarks that so long as falsification consisted merely in heightening the colour of wines with logwood and other vegetable matters it was only a semi-evil, though still considerable enough, since one of the dyes most commonly used was a drastic purgative. But magenta has now come into use on a scale scarcely to be imagined. A small commune in the neighbourhood of Béziers, containing only 1800 inhabitants, has consumed in one year 30,000 francs worth of this colour entirely for sophisticating wines.
Birmingham and Midland Institute.-The following are the lecture arrangements for the session 1876-7:This day (Friday), October 13.-Lieut. Cameron, D.C.L., on" Recent Explorations in Africa."
October 16.-Captain Davis, R.N., F.R.G.S., on
An Analytical Query.-In separating arsenic, &c., from copper' &c., by treating with an alkaline sulphide, I generally get the filtrate rather dark, and it seems to contain not copper in solution, but finely divided. I believe there is a way of preventing even a slight trace of copper getting through. I have looked at many analytical works but have failed to see anything about it, except the diluting, but that I have always done. I have taken in the CHEMICAL NEWS for years but have never seen anything on the subject.-ROBERT Monger.
"Antarctic Discovery, and its Connection with the THE COMBINED NOTE-BOOK AND
Transit of Venus, 1882.
December 11.-Prof. Boyd Dawkins, M.A., F.R.S., F.S.A., on "The Ancient Inhabitants of the Caves of Derbyshire."
January 22, 29.-E. Ray Lankester, M.A., F.R.S., on "Rots and Ferments, our Unseen Enemies."
February 5, 12.-Edward Dannreuther, on "The Pianoforte Works of Liszt and Chopin."
February 19, 26.-Prof. Sidney Colvin, M.A., on "Olympia and Greek Athletics; a Study of Ancient Usages and Recent Discoveries."
March 5.-Prof. J. M. D. Meiklejohn, M.A., on "Parody."
March 12.-Prof. Sir C. Wyville Thomson, LL.D., F.R.S., on "The General Results of the Challenger Expedition."
March 19, 26.-Prof. W. Barrett, F.R.S.E., on " Radiation and Radiometers."
April 9, 16.-George Dawson, M.A., on "Sir Walter Raleigh."
NOTES AND QUERIES.
Our Notes and Queries column was opened for the purpose of giving and obtaining information likely to be of use to our readers generally. We cannot undertake to let this column be the means of transmitting merely private information, or such trade notices as should legitimately come in the advertising columns. Fluoride of Potassium.-Can any of your readers give me a process for the ready production of luoride of potassium.-FLUORINE.
LECTURE NOTES FOR THE USE OF CHEMICAL STUDENTS preparing for Matriculation (University of London) aminations. By THOMAS ELTOFT, F.C.S., Chemical Teacher to the College of Surgeons, Science and Art Department, and other ExMatriculation Classes, St. Bartholomew's Hospital; Chemical Lecturer, City of London College, St. Thomas, Charterhouse, Science Schools, &c. Cloth, post 4to.
London: SIMPKIN, MARSHALL, and CO., Stationers' Hall Court Manchester: JOHN HEYWOOD, Deansgate.
ANDERSON'S UNIVERSITY, GLASGOW.
THE "YOUNG" CHAIR OF TECHNICAL CHEMISTRY. Professor E. J. MILLS, Dr. Sc. (Lond.), F.R.S. SESSION 1876-7.
LECTURES.-A COURSE of FIFTY LECTURES oh TECHNICAL CHEMISTRY will be Delivered duringe Session on MON DAY, TUESDAY, and WEDNESDAY in each edk, 9 a.m, beginning on WEDNESDAY, 1st NOVEMBER The Lectures will be Illustrated by the actual Inspection of Manufacturing Processes. They will include this year, as special subjects, the ALCOHOL INDUSTRY, Potable Waters, Sewage, and General TECHNICAL SANITATION. Fee for the Course Two Guineas; Laboratory Students Free.
The attention of Young Men qualifying for the Professions of Civil and Mining Engineers, Architects, &c., as well as those more immediately interested in the Study of Chemistry, is called to this Course of Lectures.
A Course of Thirty Lectures on TECHNICAL ORGANIC CHEMISTRY will be commenced on April 1st. These Lectures are more especially intended for Dyers, Colour Manufacturers, Brewers and Distillers, Tar Rectifiers, and Drysalters. Fee for the Course Two
LABORATORIES.-The Laboratories will be Open Daily, on and after Wednesday, 1st November, from 10 a.m. to 4 p.m. (Saturdays 10 a m. to 1 p.m.), under the Superintenence of the Professor and his Assistants. Instruction given in the Preparation of Chemical Substances and Original Research, especially as relating to Manufacturing Processes. Fees-Whole Session of Nine Months, £18; Six Months, £13; Three Months, £7; or for One Month, £2 105.
Students entering upon Laboratory Instruction are required have a fair knowledge of Elementary Chemistry. BURSARIES.-A Few Bursaries of £50 each per Annum, Tenable for Three Years, are now at the disposal of the Trustees, who will receive Applications in writing up to the 18th October.
166, St. Vincent Street, Glasgow,
October, 11, 1876.
ALEX. MOORE, Secretary.
Oct. 20, 1876.
Repulsion Resulting from Radiation.
VOL. XXXIV. No. 882.
fusion, and where this is impracticable mercury joints NEWS. should be used. The best way to make these is to have a well-made conical stopper, cut from plain india-rubber, fitting into the wide funnel tube of the joint and perforated to carry the narrow tube. Before fitting the tubes in the india-rubber, the latter is to be heated in a spirit flame until its surface is decomposed and very sticky; it is then fitted into its place, mercury is poured into the upper part of the wide tube so as to completely cover the indiarubber, and oil of vitriol is poured on the surface of the mercury. When well made this joint seems perfect; the only attention which it subsequently requires is to renew the oil of vitriol when it gets weakened by absorption of aqueous vapour. Cement has to be used when flat glass or crystal windows are to be cemented on to pieces of apparatus, as subsequently described (99, 102).
By WILLIAM CROOKES, F.R.S., &c.
81. THE present paper is in continuation of one which I had the honour of reading before the Royal Society, December 11, 1873, and which was published in the Philosophical Transactions, vol. clxiv., part 2, p. 501. In that paper I described various pieces of apparatus, chiefly in the form of delicate balances suspended in glass tubes, by means of which I was enabled to show attraction or repulsion when radiation acted on a mass at one end of the beam, according as the glass tube contained air at the normal pressure, or was perfectly exhausted. At an intermediate internal pressure the action of radiation appeared nil. Towards the end of the paper I said (70), "I have arranged apparatus for obtaining the movements of repulsion and attraction in a horizontal instead of a vertical plane. Instead of supporting the beams on needle-points, so that they could only move up and down, I suspend them by the centre to a long fibre of cocoon silk in such a manner that the movements would be in a horizontal plane. With apparatus of this kind, using very varied materials for the index, enclosing them in tubes and bulbs of different sizes, and experimenting in air and gases of different densities up to Sprengel and chemical vacua, I have carried out a large series of experiments, and have obtained results which, whilst they entirely corroborate those already described, carry the investigation some steps further in other directions."
82. I have introduced two important improvements into the Sprengel pump+ which enable me to work with more convenience and accuracy. Instead of trusting to the comparison between the barometric gauge and the barometer to give the internal rarefaction of my apparatus, I have joined a mercurial siphon-gauge to one arm of the pump. This is useful for measuring very high rarefactions in experiments where a difference of pressure equal to a tenth of a millimetre of mercury is important. By its side is an indicator for still higher rarefactions; it is simply a small tube having platinum wires sealed in, and intended to be attached to an induction coil. This is more convenient than the plan formerly adopted (51) of having a separate vacuum tube forming an integral part of each apparatus. At exhaustions beyond the indications of the siphon-gauge I can still get valuable indications of the nearness to a perfect vacuum by the electrical resistance of this tube. I have frequently carried exhaustions to such a point that an induction spark will prefer to strike its full distance in air rather than pass across the inch separating the points of the wires in the vacuum tube. A pump having these pieces of apparatus attached to it was exhibited in action by the writer before the Physical Society, June 20, 1874.
83. The cement which I have found best for keeping a vacuum is made by fusing together 8 parts by weight of resin and parts of bees'-wax. For a few hours this seems perfect, but at the highest exhaustions it leaks in the course of a day or two. Ordinary or vulcanised india-rubber joints are of no use in these experiments, as when the vacuum is high they allow oxygenised air to pass through as quickly as the pump will take it out. Whenever possible the glass tubes should be united by
* From the Philosophical Transactions of the Royal Society of London, vol. clxv., pt. 2.
1 Philosophical Transactions, 1873, vol. clxiii., p. 295; 1874, vol. clxiv., pp. 509, 516. Phil. Mag., August, 1874.
It would be of great service could I find a cement which is easily applied and removed, and will allow the joint to be subjected to the heat of boiling water for some hours without leaking under the highest rarefactions. Hitherto I have failed to find one which answers these requirements. I mention this in the hope that some one who happens to read this may be in possession of the recipe for such a cement, and will communicate it to me. 84. Before my first paper on this subject was read before the Royal Society I had discarded the balance form of apparatus there described, and commenced experimenting with bulbs and tubes in which quantitative results could be obtained. On December 11, 1873, when illustrating my paper, I exhibited to the Society many of these new forms of apparatus. For the purposes of simple illustrations, and for experiments where quantitative determinations are not required, I find a horizontal index suspended in a glass bulb the most convenient. The apparatus, with its mode of attachment to the pump, are shown in fig. 1.
a, b, c, d is originally a straight piece of soft lead-glass tubing 18 inches long, of an inch external and internal diameter. At one end is blown a bulb, de, about 3 inches diameter. The part a b of the tube is drawn out to about half its original diameter, and bent at right angles. The and thickened at b. tube is slightly contracted at c, and very much contracted At a it is also contracted and cemented by fusion to a narrower piece of tube bent in the form of a spiral, and fitting by a mercury joint into the
Development of the Chemical Arts.
sulphuric acid chamber of the pump. The object of the spiral is to secure ample flexibility for the purpose of levelling the apparatus, and at the same time having a fused joint. f g is a very fine stem of glass, drawn from glass tubing, and having a small loop (h) in the middle. At each end of the stem is a ball or disk, made of pith, cork, ivory, metal, or other substance. hi is a fine silk fibre made from split cocoon-silk; it is cemented by shellac at the upper end to a piece of glass rod a little smaller in diameter than the bore of the tube, and drawn out to a point, as shown. The contraction (c) in the tube is for the purpose of keeping this glass rod in its place; when properly adjusted it is secured in its place by a small piece of hot shellac, care being taken not to cement the rod all round, and so cut off the connection between the air in the bulb and that in the upper part of the tube. The silk fibre is tied on to the loop of the glass stem at h. The length of the fibre is so adjusted that the stem and disks will hang about of an inch below the centre of the bulb; that much having to be allowed for the contraction of the silk when the air is exhausted.
85. The bulb-tube is firmly clamped in a vertical position, so that the index hangs freely, and the pump is set to work, the bulb being surrounded with a vessel of water which is kept boiling all the time exhaustion goes on. The gauge soon rises to the barometric height; but the operation must be continued for several hours beyond this point in order to get the best effects. If the bulb is not heated during the exhaustion, the index loses sensitiveness after it has been sealed up for a few days, probably owing to the evolution of vapour from the pith; when, however, the precaution is taken of heating the pith the apparatus preserves its sensitiveness. On this account it is necessary to tie the silk on to the loop in the centre of the glass stem, instead of adopting the easier plan of cementing it with shellac. During the latter stages of the exhaustion, oil of vitriol (which has been boiled and cooled in vacuo) should gently leak into the pump through the funnel-stopper at the top of the fall-tube (44). This covers each globule of mercury as it falls with sulphuric acid, and stops mercury vapour from getting into the apparatus. I cannot find that any vapour is evolved
from oil of vitriol.
When the exhaustion is carried to the desired degree a spirit flame is applied to the contracted part of the tube at a (fig. 1), and it is sealed off. The apparatus is then unclamped and the tube is again sealed off at b. This double operation is necessary to secure strength at the final sealing, which can only be got by holding the tube horizontally and rotating it in the flame, watching the glass to prevent it softening too suddenly.
86. The best material of which to form the index in
these bulb-tubes is pith, either in the form of a needle or bar, or as disks at the end of a glass stem. On December 11, 1873, and again on April 22, 1874, I exhibited before the Royal Society a glass bulb 4 inches in diameter, having suspended in it a bar of pith 3 inches. It had been exhausted in the manner above described; and so sensitive was it to heat, that a touch with the finger on a part of the globe near one extremity of the pith would drive the bar round 90°, whilst it followed a piece
of ice as a needle follows a magnet.
form was devised which will be described further on (102), together with the experiments tried with it. (To be continued.)
DEVELOPMENT OF THE CHEMICAL ARTS
Chlorine, Bromine, Iodine, and Fluorine.
As leaden worms are very rapidly destroyed by liquid bromine, though very slightly attacked by bromine vapours, Frank+ employs condensing tubes of earthenbromine simultaneously evolved he avoids a too perfect ware. To separate the bromine from the chloride of refrigeration, and conducts the more volatile products, including the chlorine, into a receiver charged with ironturnings or with potash-lye. The crude bromine in the first receiver is then completely freed from chlorine and from sparingly volatile organic bromides which are usually present by fractionated distillation.
alkalies and alkaline earths deserve notice. Henner and Several methods for obtaining the bromides of the Von Hohenhausent prepare the bromides of calcium, barium, and strontium by diffusing the respective hydrates in water, decomposing with bromine, evaporating till the formation of crystals begins, and mixing the liquid with alcohol, which precipitates the last portion of the bromate formed. The bromide is then obtained from the liquid, and a further portion is procured by heating the bromate with charcoal. C. Wendler|| proposes to prepare the bromides of the alkaline earths according to Rud. Wagner's approved method for the manufacture of the corresponding iodides, i.e., by the action of bromine upon the sulphites. According to A. Faust§ Boedeker obtains the bromides as follows:-Bromide of sulphur is prepared from 20 parts flowers of sulphur and 240 parts of bromine, and gradually poured into the milk of lime made from 140 parts of quicklime, or into a corresponding solution of baryta. The bromide of sulphur in contact with the hydrate of the alkaline earth is decomposed into a metallic bromide and a sulphate. The latter is removed by the addition of alcohol and subsequently of lime. The solution of calcic or baric bromide can either be used for obtaining those salts, or for preparing the sodic, potassic, or ammonic bromide by decomposition with the corresponding carbonate or sulphate.
Casthelaz prepares bromide of sodium by forming, in the first place, bromide of ammonium by dropping bromine into liquid ammonia, and decomposes this by the addition of an equivalent quantity of caustic or carbonated soda.
Falières points out** that iodine present in bromide of
potassium may be removed by agitation with free bromine. To get the greatest delicacy in these apparatus there is Of all these methods of preparing bromides, especially required large surface with a minimum of weight (75, 76). bromide of potassium, which is most in use, none is pracThin disks of pith answer these requirements very satis- tised on the large scale. Either the ferroso-ferric bromide factorily; but I have also used disks cut from the wings is of butterflies and dragonflies, dried and pressed roseleaves, very thin split mica and selenite, iridescent films of blown glass, as well as the substances mentioned in my former paper (25). Quantitative experiments to prove this law were attempted; but the bulb apparatus was found too imperfect for accurate measurements, so another
decomposed by the addition of carbonate of potassa, or vapours of bromine are conducted into potash-lye, and he potassic bromate formed along with potassic bromide
"Berichte über die Entwickelung der Chemischen Industr'e Während des Letzten Jahrzehends."
+ Private communication.
Henner and Hohenhausen, Dingl. Pol. Journ., clxxiii., 1864, 221.