Obrazy na stronie
PDF
ePub

NEWS

after Professor Church had left, and as the College has

THE CHEMICAL NEWS. frequently been left in the charge of two, the argument

[merged small][merged small][ocr errors]

PROFESSOR CHURCH'S connection with the Royal Agricultural College will, we regret to say, shortly be severed, the only reason being, as far as we can ascertain, that he is about to marry, and therefore will be unable to reside in the College. Seeing, however, that his immediate predecessor was non-resident, we should have thought the Council would have hesitated to adopt this as their reason for depriving the College of the services of so able and experienced a chemist as Professor Church, and we shall look with some eagerness for their explanation of the circumstances.

It appears that at the beginning of February Prof. Church, who has occupied the Chair of Chemistry at the College for the last sixteen years, had an interview with the Principal, the Reverend John Constable, and informed him of his intention to marry during the coming vacation, and of henceforth discontinuing to reside in the College. This intimation the Principal regarded as a resignation of the Professorship, and wrote to Professor Church accepting the resignation. In answer to this letter, Professsor Church informed the Principal that if he decided that his Chair became vacant by the fact of non-residence it would therefore become vacant at the date previously mentioned, April 24th. He furthermore assumed that this decision was that of the Governing Body of the College, as he was elected in 1863 under the bye-law then in force, which placed the power of appointing and dismissing Professors in the hands of that body, and not under the twenty-fourth bye-law of 1870 (vide CHEMICAL NEWS, vol. xxxix., p. 105), by which this power was vested in the Principal. The matter was then referred to the Committee of Management, and on the 5th of March the following resolution was passed :

"The Committee of Management are of opinion that the discipline of the Agricultural College cannot be satisfactorily maintained except by the residence of the Professors within the walls of the College in conformity with the original bye-law No. 47. Being fully sensible of the services rendered by Professor Church during his sixteen years' residence in the College, they the more regret that they cannot accede to his recent proposal of non-residence, a compliance with it involving such alterations as would unduly disturb the present organisation of the College staff."

This decision has not only deprived the College of the services of Professor Church, but of those of his two senior colleagues, Professors Lloyd Tanner and Fream, who have respectively vacated the Chairs of Mathematics and Physics and Natural History as a protest against Professor Church's unworthy treatment.

The bye-laws of the College which we published in the CHEMICAL NEWS are perfectly unique in their way, and would seem to show that the Principal entirely supersedes the Committee of Management. He evidently considers that the Students of the College are a set of unruly schoolboys who are only to be kept in order by the strictest discipline, and that the Professors must lead the life of monks. They are not only to devote themselves day and night to the service of the College, but they are to act the muchdespised part of the "pion," or maitre d'étude of a French Lycée, and see that their young charges do not tear their clothes, tell fibs, or say naughty words. But as three Professors would have still been left to reside in the College

that Professor Church's proposal for non-residence would unduly disturb the present organisation of the College carries with it very little weight.

At

The consequences of the resignation of three senior Professors, the only University men, by the way, in the College, cannot be otherwise than disastrous. the end of this term the senior Professor will be a young man, who only two years ago was a student himself, and he will very possibly be called on to rule over students who are his seniors in years, an anomaly which cannot fail to bring about unpleasant consequences sooner or later.

We hear that a new bye-law has just been promulgated for the well-being of the future Professors. They are not to engage in any literary work without special leave from the Principal; in other words, they must take no steps to make a reputation outside the College walls without the express permission of their ruler. Had this rule obtained during Professor Church's Professorship how many valuable contributions to scientific literature would have been lost.

Such restrictions will certainly prevent any man of worth from accepting a position in the College. The Principal may, it is true, gather round him a knot of second or third rate men; but the interests of the College and, indeed, of agriculture generally, must necessarily be injured thereby; indeed, we do not see how the College can escape collapse and ultimate extinction if something is not done either by the Government or the bondholders to prevent such a catastrophe.

On looking over the list of Professors that have formerly occupied Chairs in the College we find that Principal Constable has made no less than twenty-two within the last fifteen years, more by many, we should imagine, than any other man in a similar position has made in his whole life. Professor Church has remained at the College for sixteen long years, but most of the others have left but little trace behind them. Again and again have first class men been engaged, but there has never been any inducement held out to them to cast in their lot with the College.

A contemporary gives the Principal the credit of having made the College pay, the bondholders having of late received a four per cent dividend, and something has been done towards paying off the loan, but this has only been accomplished by raising the fees from £90 to £126, by discontinuing the farm which some authorities consider to be a breach of the provisions of the Charter, the sale of the steam plough, and the most pernicious economy in every direction. Nothing is spent on the Museum, and nothing in several departments for specimens and apparatus. To have a good surplus every year is no doubt gratifying to the Council and bondholders, but even gold may be purchased at too high a rate.

We feel sure, in conclusion, that our readers will join us in expressing our sincere sympathy with Professor Church and his colleagues at thus having to sever themselves from an institution with which they were so long connected, and to which they had rendered such valuable services, as well as in paying a just tribute of admiration at the manly, straightforward, and honourable course they have taken.

Progress Effected in the Preparation of Colours Derived from Coal.-Adolphe Kopp.-The attempts made to dispense with arsenic in the manufacture of magenta have only been partially successful. The process of Coupier, who causes nitro-benzol to react upon a mixture of aniline and toluydin in presence of hydrochloric acid, is adopted in some manufactories, but it offers serious difficulties which interfere with its general employment. It is more costly and more difficult manage.-Moniteur Scientifique.

128

Filter-Presses for Chemical Works.

FILTER-PRESSES FOR CHEMICAL WORKS.

By J. MARZELL.

In this time of depression of trade it is natural that chemical manufacturers should pay more attention to those kinds of apparatus which, by a surer and better working, enable them to increase the yield, and permit quicker passing through the intermediate stages of the processes, thus giving to a plant a higher working power and efficiency. Among that class of machinery the so-called "filterpresses" undoubtedly hold one of the foremost places, and their being taken up so rapidly-especially in the last year-surely speaks in their favour.

The principle of the filter-presses is generally known; it is a filtering under pressure, for the object of— (a) Filtering the largest possible quantity of fluid-consequently solids in comparison-through the smallest possible filter space.

(b) Freeing the residue remaining in the filter as much as possible from the filtrate.

Both points are realised by the pressure applied in filling the filter-presses, and generally amounting to 120 lbs. per square inch. At the same time the filter-press represents the most convenient arrangement of filter cloth, as a very large surface is brought into a very small space. In the largest size presses over 425 sq. feet effective filtering surface are arranged in a box, if I may call it so, of 4 sq. ft. to 9 sq. ft. General rules of yields cannot be laid down, as specific gravity and physical properties of the different stuffs are important points to deal with. The greatest difficulty for chemical works always was to find a press suiting the different stuffs and operations, as these in most cases cannot be altered or modified without losing on the other side all advantages the filter-presses might have promised. It was therefore only natural that the massive and enormous wooden cubes brought out at first, with their elaborate handling, had soon to make room for lighter constructions, with a number of improvements in many directions.

An important improvement has recently been made by M. A. L. G. Dehne. I refer to a new arrangement for an absolute outwashing of the press cakes in the press itself under the following conditions:

(a) To use as little wash water as possible. (b) To remove the last traces of soluble substance out of the cake, to wash absolutely or completely be it either to wash the cakes, as the valuable part "neutral," as I may term it (as required with alizarin, tartrate of lime, blanc fix, &c.), or to separate the valuable soluble substances from the worthless residues without any loss, and to get

the wash liquors in a concentrated state, the latter being of great importance for a following concentration for crystallisation (as with sugar, citric, tartaric acids, alum, sulpho-salts, &c.) (c) To do all that in the shortest time possible. In the old method of washing the water was introduced on the top of the cakes, trickling through the same, taking up in its way the soluble substances it met with, and leaving the press by the cocks. Every manufacturer acquainted with these presses will have found that it takes a long time, and is seldom possible, to remove the last parts of soluble stuff, and therefore it was preferred in many cases to take out the cakes, boil them up with water, and to re-filter-press them; in many cases even repeating the operation several times.

{CHEMICAL NEWS

March 23, 1879.

able is proved by the fact that in the manufacture of china and faience the cakes of clay coming out of the presses never can be used on the chairs before having passed cutting and kneading machinery, as in baking the air would form bubbles on the goods. In the washing process the air prevents the wash liquor from a thorough penetrating of the cakes. The water coming from above would not remove but only dislodge the air. The consequence of that was the conclusion to let the wash liquor enter at the bottom and make its way upwards, driving thus the air before it, which is removed by a system of air channels and escapes, with a whistling noise, out of a mouthpiece.

The other disadvantage of the old system was the following:-The water entered on the upper edge of the cake in two streams of about in. thick. By the presnaturally tried to find the most direct way to the outlet, sure the washing was applied and the two streams and that is the line drawn from their point of entrance to the outlet cocks! Besides that, the way was regulated by the little air-bladders forming a regular kind of network in the cake. The result was that the streams, instead of equally impregnating the material, only parted themselves in the cakes, so to say, forming a system of small rivers, the islands of which never came under the influence of the water.

To do away with this irregularity M. Dehne covered the channelled surfaces of the press plates inside; the chambers with perforated sheets of metal, and now in washing brought the water into the space formed between the channelled surface and the perforated plate. Thus on both sides of the cakes in this way walls or plates of water are produced, which by the hydraulic acting pressure are driven diametrically into the cakes. With a cake of 1 in. thick the water has only to move in. to join the liquor coming from the other side. As the air has been removed beforehand, each molecule of the stuff in the presses is now brought into contact with the water, which thereby has full power to take up all soluble particles. The arrangement allows at the same time to regulate the pressure under which the extraction takes place.

So far the theory. The practice, by working on large scales under different circumstances and with different materials, has given the best results.

As example I give the returns of the K. K. Zuckerfabrik Swolonowas (Austria), which were kindly placed at my disposal. The material is the product of precipitating saccharate of lime with carbonic acid, thus yielding carbonate of lime, mixed with sugar syrup, which latter has to be removed.

showing 125 square ft. filtering surface proved for 120 lbs. "The presses are such with 18 chambers of M. Dehne's, per square inch."

1=

Filling of press = 30 minutes; washing absolutely = 18 minutes; emptying and starting = 6 minutes; together 54 minutes. The weight of the extracted cakes out of one press, 315 lbs. (157 k.); the cakes are hard.

The extracted cakes were entirely free from sugar. gals. (176 litres). Density of the entire wash-liquor = The quantity of wash-water used for one press = 39 523 balling and 4:11 per cent sugar.

(This for the reason in the arrangement that the washThe filter cloth has not to be removed for a fortnight. liquor takes the opposite way of the filtration, thus always cleaning the pores of the cloth.-J. M.) The firm receives daily 13 tons (13,627 k.) of the washed-out residues. The ap-2:46 per cent of sugar, which it was not economical to corresponding residues of the old presses retained about regain, and the firm reckon the net gain they have by putting up Dehne's new presses with absolute extraction with 47 tons (47,400 k.) of sugar in a campagne of 150 days, representing a value of £1422 (14,220 Austrian florins).

The reason of this improper acting of the washing paratus is the insufficient distribution of the wash liquor

in the cakes, caused

(a) By the construction.

(b) And principally, by the air enclosed in the cakes. Especially is this last point of great importance. That the amount of air in the cakes is consider

The quicker working and the advantage of getting pretty

[ocr errors]

CHEMICAL NEWS, 1 March 28, 1879

concentrated liquors into the evaporating pans need not be mentioned.

Another example. The quick extraction of valuable cakes is given in the manufacture of the artificial alizarin material; alizarin paste must be freed from the sulphate of soda. With the old presses the washing was going on twelve to fourteen hours before the charge of a press with 18 chambers was finished. The new presses with absolute extraction-according to the returns of an alizarin works using twelve of these new presses-only wanted 35 to 45 minutes for the absolute neutralisation of a properly precipitated paste. In this case a secondary but important advantage of the new process can be seen. In washing there is always some alizarin taken up into suspension and washed away, especially in the last hours, when the water is running pretty clear. As with the new presses the time, as well as the quantity of water, are decreased considerably, this loss is reduced to a minimum. Of great weight this point is in the treatment of such substances, which themselves are slightly soluble in water. I only mention tartrate of lime.

Notwithstanding their short life the new presses with absolute extraction have been taken up by a great many firms. Like most new things they have often to meet with mistrust and criticism in sometimes the most incomprehensible form. From the representatives of progress, however," the go ahead people," the new apparatus everywhere meets with the greatest interest and acknowledgment of its practical advantages, and the large number of these presses already delivered to various branches of different countries may be proof of their value. 41, Woburn Place, London, W.C.

ON INDIGO.BLUE FROM

POLYGONUM TINCTORIUM AND OTHER
PLANTS.

By EDWARD SCHUNCK, Ph.D., F.R.S.
(Continued from p. 120).

THE preceding experiments lead to the conclusion that the leaves of Polygonum tinctorium contain a substance not to be distinguished from the indican of Isatis tinctoria, which by decomposition with acids, yields indigo-blue and glucose, accompanied by some by-products, and that there is no proof of the existence of ready-formed colouring. matter in the plant while the latter is living and in a healthy state. The pre-existence of indigo-blue, or of its hydride, indigo-white, in these plants was taken for granted forty or fifty years ago when the class of bodies which we now call glucosides and the peculiar kind of decomposition which they undergo were unknown. Even now a superficial examination of some phenomena would almost certainly lead to the conclusion that the indigo-blue is formed by the action of air, i.e. in conseqence of the oxidation of some easily oxidisable substance in the plant, Bearing in mind, however, with what extreme facility indican is decomposed, its watery solution on standing some time, even at the ordinary temperature, depositing indigo blue, I think it will not b difficult to explain all the phenomena hitherto observed by myself and others.

On taking a plant of Polygonum tinctorium and making incisions with a penknife in the leaves between the main vessels, or crushing the soft parts of the leaves here and there with an agate pestle, then, after a short time plunging the whole plant into boiling alcohol to remove the chlorophyll, it will be found that those parts of the leaf which have not been injured, become white or retain only a faint yellow tinge, while those parts that have been cut, crushed, or otherwise injured, show a blue colour, the colouration extending for some distance inwards from the place where the lesion occurred, the most intense colour

being at the edge of the cut or bruise. So, too, in the living plant, when some injury accidentally occurs to a leaf, the part injured will appear blue. Nothing can be more natural than to suppose that in these cases the blue colouring-matter is formed by the action of the air, i.e. by the oxidation of some substance which escapes from the cells in consequence of organic lesion, just as the surface of a freshly cut apple or pear becomes brown on exposure. If a plant of Polygonum tinctorium be immersed in water, and the water be frozen by surrounding the vessel containing it with a freezing-mixture, it will be found, after complete thawing, that the leaves or parts of leaves which have been throughly frozen appear of a dark colour and are quite flaccid; and if the plant be then immersed in boiling alcohol so as to dissolve the chlorophyll and other matters, those very parts show afterwards an intense blue colour, while those portions which had remained unfrozen appear almost colourless. This experiment, which had already been made by Joly, was considered by him to prove the pre-existence of indigo-blue in the plant-though why, if this were the case, the colouringmatter should not make its appearance in the unfrozen portions of the leaf, I am at a loss to understand. The fact that a fresh leaf of Polygonum tinctorium, if immersed in alcohol or ether, appears blue after the chlorophyll has been removed, has also been considered to prove the pre-existence of indigo-blue in the cells. This phenomenon is always observed when the leaves are immersed in cold alcohol, and more distinctly when ordinary spirits of wine are taken than with absolute alcohol. Á very simple experiment suffices, however, to prove that in this, as in all the other cases, appearances are deceptive. If freshly gathered leaves of Polygonum tinctorium are plunged at once not into cold, but into boiling alcohol, the whole of the colour is soon removed, the leaves retaining only a faint yellow tinge. On now simply evaporating the green alcoholic liquid, not a trace of indigo-blue will be found in the residue. It is therefore absolutely certain that the leaves contain no ready-formed colouring-matter; for so stable a body as indigo-blue could not possibly be decomposed or be made to disappear by the action of boiling alcohol only. It must necessarily appear either in the alcoholic extract of the leaves or in the residual portion left by the alcohol.

A very simple explanation offers itself, I think for all the phenomena hitherto observed. Indican, the mother substance of indigo-blue, is a body the molecules of which are in a state of unstable equilibrium. As long as it is contained within the cells of the plant the vitality of the cells keeps it in its original unchanged condition. As soon, however, as this vitality is destroyed (whether by organic lesion, by extreme cold, or by any other means), the indican begins to undergo decomposition, the mole. cules rearrange themselves in the order to which their chemical affinities predispose them, and the compound splits up into indigo-blue and indiglucine, this taking place so rapidly that in certain cases it would appear as if the colouring-matter pre-existed in the plant. If (to take the simplest case) the leaves as soon as gathered are immersed in cold spirits of wine or in cold ether, the vitality of the cells is thereby destroyed; and the indican contained in them is then in part decomposed, yielding indigo-blue, which remains undisolved, imparting a more or less distinct blue tint to the leaves. When boiling spirit of wine is taken, the indican is extracted before it can undergo decomposition, and dissolves in the spirit. It may be detected in the residue obtained on spontaneous evaporation of the alcoholic extract by its property of yielding indigoblue on decomposition with acids as above described. It is posible that the leaves contain some ferment which hastens the decomposition of the indican as soon as vitality has ceased; but I have no positive evidence to offer in favour of this view.

I may, in conclusion, describe another experiment, which, though it teaches nothing new, confirms what I have just stated, and is interesting in its way. Having cut some

[blocks in formation]

sprigs of Polygonum tinctorium, about six inches long, I immersed the cut ends in dilute hydrochloric acid (consisting of one part of acid of specific gravity 1.15 and ten parts of water), and left them to stand for several days exposed to the sun and air. The acid was gradually absorbed, ascending through the stems, first into the lower leaves, then into the higher ones. The gradual absorption of the acid was distinctly seen by the discolouration of the leaves, which commenced at the basis of each leaf and extended towards the apex, the lively green colour being changed into a dirty yellow. After some time this colouration was followed by a dark blue one, commencing at the base of each leaf and extending towards the apex, but never quite reaching the latter except in the lower leaves. When the change in colour had begun to show itself in the upper tenderer leaves, the whole showed symptoms of fading, all further power of absorbing the acid liquid seemed to be lost, and the sprigs were then at once immersed in hot spirit of wine. After remaining in the spirit until the chlorophyll was removed, the part of each leaf which had undergone a change appeared blue, whilst the part into which the acid had not penetrated appeared almost colourless. In this case it is probable that the indican was decomposed not so much in consequence of the loss of vitality in the cells as by the direct action of the acid. In some of the leaves there was another distinct blue colouration towards the apex, in the part to which the acid had not penetrated, separated from the blue part at the base by a white zone. This second colouration may be attributed to the loss of vitality in that part of the leaf.

All these experperiments must be made with plants whilst in a state vigorous growth. If made when the season is advanced (that is, ofter the flowers have begun to appear), the leaves, though apparently unchanged, show only traces of blue colour after treatment and subsequent immersion in hot alcohol. This shows either that the indican has disappeared, being applied to other purposes in the economy of the plant, or that it has undergone the peculiar molecular change before referred to, into a substance which no longer yields indigo-blue by decomposition, but indirubine and other products. The latter is the more probable way of accounting for the difference; for the parts of the leaf which have been accidentally injured by the bites of insects or from other causes at the later stage of the plant's development become red, not blue, as at the earlier stages. This red colour disappears on immersion of the leaves in hot alcohol, the indirubine, to which it is probably due, being more soluble in that menstruum than indigo-blue.

The leaves of Polygonum tinctorium in which the blue colour has been developed by any of the means described, exhibit even to the naked eye, and still more distinctly when examined under the microscope, certain appearances

which are not without some interest.

1. The colouring-matter seems to be confined to the parenchyma of the leaf. fications in the leaf are free from it, so that in the coloured leaf the vessels may be distinctly traced as white veins on a blue ground. Even the cells of the parenchyma adjacent to the vessels are much less coloured than those a little further off, which produces the effect of a gradual shading of colour from the white of the vessels to the dark blue of the remoter cells. The cells of the leafcuticle are also free from colouring-matter.

The stem and its fibrous rami

2. The younger leaves at the summit of each branch generally show a more intense colour than the older ones near the base. Each leaf probably contains the same amount of colouring-matter; but in the lower leaves it is more widely distributed.

CHEMICAL NEWS,
March 28, 1897.

The colouring

this is found, however, not to be the case. matter is discovered within the cells of the parenchyma in the shape of separate dots and parcels of various sizes, and apparently in an amorphous state, the cell-wall being quite colourless. These dots and parcels being very numerous, produce, when seen in the mass, a uniform blue colouration, more or less intense. The darker colour of some leaves is simply the effect of a greater crowding of the blue particles in each individual cell, the cells of the paler leaves containing fewer of these little masses, sometimes hardly any.

Mr. Charles Bailey, to whom I gave some specimens of leaves of Polygonum tinctorium coloured blue, had the kindness, at my request, to submit them to microscopic examination, and gave the following as his opinion thereon:

"The colouring-matter left in these specimens would seem to be what Nägeli terms 'crystalloids;' and, with one exception, these bodies are, as far as my examination has gone, confined to the interior of the cells of the parenchyma. I do not see the least trace of any of this colouring-matter occurring in the intercellular spaces. The only part of the tissue where I find it, other than the parenchyma, is in the cells of the stomata; but it occurs nowhere else in the cuticle."

(To be continued.)

PROCEEDINGS OF SOCIETIES.

CHEMICAL SOCIETY. Thursday, March 20, 1879.

Dr. J. H. GLADSTONE, F.R.S., President, in the Chair. AFTER the announcement of visitors the minutes of the previous meeting were read and confirmed. The following certificates were read for the first time :-W. Johnstone, W. B. Turner, C. Slater, T. Palmer, A. H. Black, W. A. Bradbury.

The PRESIDENT then called on Dr. FRANKLAND to read a paper on "Plumbic Tetrethide," by E. FRANKLAND and A. LAWRANCE. This substance was discovered by Buckton in 1859. The authors prepared the compound as follows:Plumbic chloride is added to zinc ethyl contained in a stout glass bottle as long as any reaction takes place. and distilled (from an oil bath) in a current of steam. The product is mixed slowly with a large volume of water, The distillate separates into water and a heavy layer of plumbic tetrethide. During the preparation no gas was evolved, and the authors infer that the decomposition has two stages, PoCl2+2ZnEt2= PbEt2+2ZnEiCl and 2PbEt2=Pb+ PbEt4. The following gases have no action monia, carbonic anhydride, carbonic oxide, cyanogen, at ordinary temperatures on plumbic tetrethide :-Amnitric oxide, oxygen, sulphuretted hydrogen. Sulphurous anhydride is rapidly absorbed and the liquid plumbic tetrethide converted into a white amorphous solid. This product was placed in a beaker, over which was inverted a second beaker, the two being luted with gummed paper. On heating the lower beaker with steam, crystals sublimed, which, after purification from a volatile lead compound by treatment with strong nitric acid, evaporain chemical composition and physical properties to be tion to dryness, and re-crystallisation from alcohol, proved identical with diethyl-sulphone, SO2Et2. The residue after the sublimation of the diethyl-sulphone consisted principally of plumbic ethyl-sulphinate, SOEtPbO" SOE

3. The intense and apparently uniform colouration of some of the leaves might lead to the conclusion that the cellular tissue is itself dyed blue-which would not seem improbable considering the affinity which indigo-blue shows for cellulose, as seen in the blue-dyeing of cotton fabrics. On examining the leaf-cells under the microscope, Ethyl-sulphinic acid may be considered as sulphurous

NEWS

JC2H5
[соно

(C2H5
SOHO

No volatile organo-metallic base was detected in the pro-
duct of the action of SO2 on PbEt, similar to that produced
in the corresponding reaction with stannic ethide.
In answer to a question of the PRESIDENT,

acid, SOHO2, in which a semimolecule of ethyl has re- | were also made with sealed tubes. The authors conplaced one of hydroxyl, SOEtHO, or as propionic acid include that sulphur decomposes water, uniting both with which one atom of tetrad-sulphur has been substituted its oxygen and hydrogen, the decomposition being indefor one of carbonpendent of atmospheric oxygen. The authors repeated their experiments with sulphur purified by treatment with potassium permanganate, and find that the reactions above described remain unaltered. Selenium and tellurium have an appreciable action on water at 160°. Amorphous phosphorus does not decompose water at 100°. At 160° a small quantity went into solution. When lead acetate solution was substituted for water, metallic lead, phosphate, and phosphide were formed. With copper sulphate metallic copper was deposited with phosphide and sulphide, phosphoric and sulphuric acids being also formed; cupric chloride at 160° is first reduced to cuprous chloride, phorus does not decompose boiling water except in the and finally converted into a phosphide. Vitreous phospresence of oxygen; it reduces metallic (lead acetate) solutions even when oxygen is excluded. Bromine and iodine, when heated with excess of water, dissolve in bromine be treated with lead acetate, lead bromide and small quantity as alkaline bromides, bromates, &c. If

Dr. FRANKLAND said that plumbic tetrethide could be prepared directly without the intervention of zinc ethyl, | but the product was small in quantity and impure.

Prof. W. FOSTER then gave a verbal communication "On the Production of the Higher Oxides of Iron, Chromium, Manganese, and Bismuth." Prof. Foster said that the observations he had to make were a continuation

of a paper which he had recently communicated to the Society. When a strongly alkaline solution of sodic hypobromite is heated with a solution of potassic ferrocyanide the solution rapidly becomes deep red from the formation of a ferrate. Almost any iron compound, and even freshly precipitated ferric hydrate can be substituted for the ferro-cyanide in the above reaction. The author has not attempted to isolate the potassium or sodium ferrate formed under these circumstances. Similar reac tions occur if manganese, chromium, or bismuth compounds be boiled with alkaline hypobromite, permanganate, chromate, &c., being formed. Oxygen is evolved during the reaction. Cobalt, nickel, and copper salts also evolve oxygen. The author demonstrated this fact in the case of cupric sulphate, a considerable quantity of oxygen being collected when the sulphate was mixed with alkaline hypobromite, and the mixture heated to about 20' C.

Dr. WRIGHT said that some samples of bleachingpowder when closely stoppered were apt to explode: (he had always found manganese in these samples). Possibly this might be accounted for by the evolution of oxygen by a reaction similar to that described by the author.

Mr. NEISON asked if Prof. Foster had noticed any formation of a green manganate in the oxidation of manganese compounds. Some time since he was working with ferrates, and obtained once a green iron acid which he had never seen since. Perhaps by these reactions it might be obtained.

Mr. HARTLEY had noticed that when the copper sulphate and alkaline hypobromite were first mixed the solution turned yellow, but when the evolution of oxygen ceased the liquid was quite dark. This yellow substance was probably Brodie's cupric peroxide.

Mr. KINGZETT had made some experiments on the action of oxide of manganese on bleaching-powder; oxygen was evolved, but the gas was not pure.

Prof. FOSTER, in answer to a question of the President, said that he had not tested the oxygen evolved quantitatively as to its purity.

The next paper was read by the SECRETARY, "On the Decomposition of Water by certain Metalloids," by C. F. CROSS and A. HIGGINS. The statements of chemists with respect to the action of sulphur on water are conflicting. Mulder affirms that the vapour of water reacts on sulphur at a high temperature to form penta-thionic acid. Myers asserts that hydrogen sulphide and thiosulphuric acid are formed. Girard also found that hydrogen sulphide was evolved by boiling sulphur with water. Geis ascribes this evolution to impurities in the sulphur. The authors therefore investigated the reaction of sulphur with water. Water containing "flowers of sulphur" in suspension was boiled, and the vapour conducted into lead acetate. The latter was continuously decomposed with the formation of sulphide. The quantity formed under various conditions was estimated. The reaction which occurs is probably 2H2O+S3=2H2S+SO2. If air be present sulphuric acid is also formed. Some experiments

dioxide are formed.

Mr. WARINGTON remarked that an Italian chemist had

observed that gypsum was formed by the action of calcium carbonate on sulphur in the presence of moisture.

The next paper was read by the SECRETARY, "On the Volumetric Determination of Chromium," by W. J. SELL. The author having discovered that chromium in ordinary chromic salts can be completely converted into chromic acid by means of potassic permanganate, endeavoured to apply this reaction directly for the estimation of chromium. He was, however, unsuccessful, owing to the separation of manganese dioxide. He has devised the following method, which yields rapid and accurate results. The solution, containing chromium acidified with sulphuric acid, is boiled, and a dilute solution of permanganate added to the boiling liquid until a purplish tint remains after boiling for three minutes. The solution is then rendered slightly alkaline with sodic carbonate, alcohol is added, and the manganese filtered off. The chromic acid in the filtrate is estimated by titration with iodine and sodic thio-sulphate. The author has successfully applied the method to the estimation of chromium in chrome iron ore. He recommends the following plan of effecting its decomposition. The chrome iron ore is placed on the top of about ten times its weight of a mixture composed of one molecule of well-fused and powdered sodium bisulphate to two molecules of sodium fluoride, and the whole is ignited for fifteen minutes. An amount of sodium bisulphate is now added equal to that of the mixture taken, and when thoroughly fused a further addition of an equal quantity of bisulphate is made, the mass fused, and then rapidly cooled. The fused mass so obtained dissolves completely in boiling water acidified with sulphuric acid. In this way a determination can be made in an hour and a quarter. The author's attention has been directed to a notice by Mr. Wanklyn in the Phil. Mag., February, as to the conversion of chromic oxide into chromate by alkaline permanganate. This result the author arrived at some months ago, but has not yet succeeded in applying it quantitatively.

During the reading of the last paper Dr. RUSSELL occupied the Chair.

The anniversary meeting will take place on Monday, March 31. The next ordinary meeting will be on April 3, when the following papers will be read :-" On Terpin and Terpinol," by Dr. Tilden; "On the Transformation of Aurin into Trimethyl-para-rosanilin," by R. S. Dale and C. Schorlemmer; "On a Gold Nugget from South America, by Mr. Attwood; "On the Solution of Aluminium Hydrate by Ammonia, and a Physical Isomeride of Alumina," by C. F. Cross.

« PoprzedniaDalej »