Obrazy na stronie


Nov. 24, 1876.

Chemical Notices from Foreign Sources.

Before writing this I have taken great pains to understand Major Ross's paper, and I could almost say that I do so were it not for the sentence which occurs at the end of his fifth paragraph. But here I frankly admit I have failed. After experimenting upon all the known relations of "that that " to "this," and of "that this" to "that" by analysis and synthesis (and, I had almost said, the "sodium hypothesis "), I have been obliged to abandon the problem.-I am, &c.,



To the Editor of the Chemical News. SIR, Mr. Caspers' remarks on my investigation on anthracene testing require my immediate reply.

Mr. Caspers is guilty of a singular want of tact, by first obtaining from me private information, and an exceptional sample of anthracene, and then utilising the same in contradicting my statements, withour informing me of his intention to do so. Such conduct is happily unknown in the scientific world, or there would soon be an end of all free exchange of ideas on scientific matters. But Mr. Caspers is no chemist, and I cannot discuss with him theoretical questions: his observations on my results are valueless.

Mr. Caspers, with charming simplicity, shows his ignorance of the first rudiments of chemistry when he says "Nearly all coal-tar distillers, even those who work under the direction of efficient chemists, have unpersuadedly to believe that the specific gravities of quinone and anthracene are in proportion like 1000: 856."

Apart from the mass of confused ideas compressed into a few lines, the fact clearly stands out that the writer does not know the difference between specific gravity and atomic weight, and I must simply decline to notice any future criticisms coming from such doubtful authority. I am, &c., FREDERICK VERSMANN.

35, Whitecross Place, Wilson Street, Finsbury, E.C.



ment. It is very adhesive; though mat, it is capable of taking a fine polish, and may be introduced in the decoration of objects of art. Antimony can be deposited from a solution of the double chloride of antimony and ammonium at common temperatures. It frequently serves to replace platinum-black in a number of fine art manufactures. Deposits of palladium are obtained with ease by means of the double chloride of palladium and ammonium, either with or without the battery. The solution must be perfectly neutral.

New Dynamo-Magnetic Phenomenon. MM. Trève and Durassier.-Let there be a horse-shoe magnet, of any length, covered upon one side with varnish, or, better, with a plate of glass. If there is laid upon the neutral part a cylinder of soft iron, it is seen to move towards the poles, which it reaches in a time which is a function of the weight of the cylinder and of the coercitive force of the magnet. Hence there results a new method of estimating the magnetic force by the mechanical work which it effects.

Detection of Magenta in Wine.-M. E. Bouilhon.Five hundred c.c. of wine are placed in a capsule, raised to a boil, and evaporated down to 125 c.c.; the capsule is then withdrawn from the fire, and 20 grms. crystalline hydrate of baryta are added. It is agitated to facilitate the reaction, allowed to cool, poured upon a filter, and the precipitate washed with distilled water, so as to obtain in all 125 c.c. of filtrate. It is then necessary to ascertain, by the addition of a few crystals of hydrate of baryta to the filtered liquid, that the precipitation of the colouring matter of the wine is complete: if not, more hydrate of baryta must be added, and the liquid re-filtered. It is then introduced into a flask containing about 250 c.c., with 50 settle. When the ether is completely separated from the to 60 c.c. of pure ether, strongly shaken, and allowed to aqueous liquids it is drawn off by means of a pipette, and poured into a porcelain capsule. A drop of acetic acid at 8° is added, 3 or 4 drops of distilled water, and a little white unwoven silk, consisting of ten threads a centimetre in length. If the quantity of magenta contained in the wine is at all notable acetic acid produces at once a rose colouration, but when only minute traces are present the ether is allowed entirely to evaporate. The residue consists of a small quantity of aqueous liquid, in which the

FOREIGN silk soaks. The capsule is then very gently heated, so as to evaporate the bulk of this liquid, and concentrate the traces of colouring matter in a few drops, thus favouring its fixation upon the silk. This process, if carefully executed, reveals one hundred-millionth part of magenta

NOTE.-All degrees of temperature are Centigrade, unless otherwise in wine. expressed.

Comptes Rendus Hebdomadaires des Seances, de l'Academie des Sciences. No. 19, November 6, 1876. Researches on the Production of Electro-Chemical Deposits of Aluminium, Magnesium, Cadmium, Bismuth, Antimony, and Palladium.-M. A. Bertrand.The author has obtained deposits of aluminium on decomposing with a strong battery a solution of the double chloride of aluminium and ammonium. A plate of copper, forming the negative pole, whitens gradually, and becomes covered with a layer of aluminium, which takes a brilliant polish under the burnisher. The double chloride of magnesium and ammonium in an aqueous solution is readily decomposed by the battery, giving in a few minutes strongly adherent and homogeneous deposits of magnesium upon a sheet of copper. It polishes readily. The battery must be powerful. Cadmium is best deposited from the bromide to which a little sulphuric acid has been added. It is then very coherent and very white, and takes a fine polish. The sulphate, if acidulated, also gives an immediate deposit of metallic cadmium, very adhesive, and capable of a fine polish. Bismuth is deposited from a solution of the double chloride of bismuth and ammonium upon copper or brass by the current from a Bunsen ele

Reimann's Farber Zeitung.
No. 39, 1876.

Pittakall is manufactured by a company in Hanover under the name of violacein.

The use of vanadic aniline-blacks is greatly on the increase in France. The colour obtained is fast, both as against milling and acids.

shades obtained are reported to resemble the colour of the Mahogany is again recommended as a dye-ware. The wood itself, and to be very fast. The mordants used are acetate of alumina for cotton, and sulphates of iron and copper for wool.


Organisation Among Chemists.-The adjourned meeting to discuss this subject assembled in the Chemical Society's Room, Burlington House, on Saturday, November 4th, 1876. Prof. F. A. Abel, F.R.S., President of the Chemical Society, in the Chair. The minutes of the previous meeting were read and confirmed. The


Organisation among Chemists.


Report of the Committee appointed to confer with the
Council of the Chemical Society was read. It was pro-
posed by Mr. J. A. Wanklyn and seconded by Prof.
Redwood:-" That the cordial thanks of the meeting be
tendered to the President and Council of the Chemical
Society for the consideration given by them to the pro-
posals of the Organisation Committee, and for the efforts
made by them to meet the views of the Committee in
relation to these proposals." (Carried unanimously.)
was proposed by Prof. Frankland, F.R.S., seconded by
Dr. Voelcker, F.R.S., and supported by Dr. Williamson,
F.R.S.:—“That, having regard to the limited powers of
the Chemical Society under its charter, it is desirable that
an Association be formed that shall be independent of
the Chemical Society, and that the Organisation Com-
mittee already formed be dissolved, and that the following
gentlemen, or such of them as may be willing to act, form
a new Committee (with liberty to add to their number)
to settle the form and details of the scheme, and to take
all steps necessary to secure the formation and incorpora-
tion of the proposed new Association." (Carried unan-
imously.) The proposed Committee are the following:-
Prof. Abel; Mr. A. H. Allen (Sheffield); Dr. H. E. Arm-


strong; Prof. Attfield; Mr. James Bell; Mr. I. Lowthian

Bell (Middlesbrough); Prof. Bloxam; Prof. Crum Brown
(Edinburgh); Mr. M. Carteighe; Mr. Dugald Campbell;
Mr. W. Crookes; Mr. G. E. Davis (Runcorn); Dr. Dupré;
Prof. James Dewar (Cambridge); Mr. F. Field; Mr. R. J.
Friswell; Prof. Frankland; Prof. Gladstone; Mr. George
Gore (Birmingham); Prof. Galloway (Dublin); Mr. C. E.
Groves; Mr. W. N. Hartley; Mr. C. W. Heaton; Mr.
Douglas Hermann (St. Helens); Mr. David Howard;
Mr. C. T. Kingzett; Prof. Marréco (Newcastle); Mr. F.

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Nov. 24, 1876.


Cantor Lectures.

Anthropological Institute, 8.

Manchester Literary and Philosophical Society, 7.

WEDNESDAY, 29th.-Society of Arts, 8.
THURSDAY, 30th.- Royal, 4. (Anniversary.)
FRIDAY, Dec. Ist.-Geologist's Association, 8.

SATURDAY, Dec. 2nd.-Physical, 3. "On some Mechanical Illustra-
tions of Thermo-Electric Phenomena," by
O. J. Lodge, B.Sc.


7. J.L.-We should think there is alum in the paste. G. M.-The part of the Report to which you refer has not yet appeared in our columns.

R. L.-Dr. Versmann's letter renders the publication of your's un


ERRATUM.-Page 212, col. 1, line 3 from top for "250° C." read "275° C."


Now ready, Fourth Edition, with Engravings, 8vo., 7s. 6d.,


ANALYSIS. By WILLIAM G. VALENTIN, F.C.S., Principal Demonstrator of Practical Chemistry in the Royal School of Mines and Science Training Schools, South Kensington.

J. and A. CHURCHILL, New Burlington Street.

Second Edition, in One Large 8vo. Volume of 550 pages, strongly
bound in cloth, Illustrated with numerous Wood Engravings,
and 57 Specimens of Printed and Dyed Fabrics,
Price 21s.

A. Manning; Dr. E. J. Mills; Dr. Hugo Müller; Mr. E. DYEING AND CALICO

Neison; Prof. Odling (Oxford); Mr. F. J. M. Page; Mr.
J. Pattinson (Newcastle); Dr. B. H. Paul; Mr. W. H.
Perkin; Mr. C. H. Piesse; Prof. Redwood; Prof. Emer-
son Reynolds (Dublin); Dr. W. J. Russell; Dr. R. Angus
Smith (Manchester); Dr. H. Sprengel; Dr. Stevenson;
Mr. R. Tatlock (Glasgow); Mr. E. T. Teschemacher;
Prof. R. V. Tuson; Dr. Voelcker; Mr. J. A. Wanklyn;
Prof. Williamson; Mr. J. T. Way; Dr. C. R. A. Wright.
A vote of thanks to the Chairman (Prof. Abel) for presiding
was carried by acclamation, and a vote of thanks to the
Secretaries terminated the proceedings. The majority of


including an account of the most recent improvements in the Use and Manufacture of Aniline Colours.

By the late

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A. Keiffenheim and Co., 27, Side, Newcastle-on-Tyne.

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New Work by Professor Hayden.-An important work is now being issued by Prof. F. V. Hayden, whose name is a sufficient guarantee of its scientific value. The title is "The Yellowstone National Park and the Mountain Regions of Portions of Nevada, Idaho, Colorado, and Utah," by Prof. F. V. Hayden, Geologist-in-charge of the U.S. Government Expeditions to the Yellowstone Valley of the years 1871 and 1872, and of the U.S. Geological and Geographical Survey of the Territories. The work is illustrated by chromo-lithograghic reproduc- The Justices of the County of Worcester are

tions of water-colour sketches taken by Thomas Moran. The price for the complete work, 5 parts, with text, is 50 dollars. The text will be published simultaneously in English, French, and German. The list of plates includes Hot Springs of Gardiner's River, Yellowstone National Park; The Great Blue Spring of the Lower Geyser Basin, Yellowstone National Park; The Castle Geyser-Upper Geyser Basin, Yellowstone National Park; Lower Yellowstone Range, Yellowstone National Park; Yellowstone Lake, Yellowstone National Park; Tower Falls and Sulphur Mountain, Yellowstone National Park; Head of Yellowstone River, Yellowstone National Park; The Grand Canon, Yellowstone, Yellowstone National Park; The Towers of Lower Falls, Yellowstone National Park; The Mountain of the Holy Cross; The Mosquito Trail,



desirous to appoint a person, "possessing competent knowledge, skill, and experience," as ANALYST OF ARTICLES OF FOOD AND DRUGS sold within the County.

The duties of such Officer are to analyse any articles of food and drugs which may from time to time be submitted to him by the proper authority, and to furnish Certificates of the result of such Analyses. The person appointed will be required to reside in or near the City of Worcester. He is prohibited by the Statute from being enghe sale of food or drugs within the County, but may practise as engaged, directly or indirectly, in any trade or business connected an analytical and consulting chemist, physician, or surgeon. The salary will be £100 per annum.

Applicants for the appointment are requested to send a statement of signed, on or before the 4th day of DECEMBER next. their qualifications, with original or copy Testimonials, to the under

County Hall, Worcester,
November 15, 1876.

Clerk of the Peace.

Rocky Mountains of Colorado; Summit of the Sierra Wanted, a Chemist thoroughly accustomed to

Nevada; Great Falls of Snake River; Valley of Babbling
Waters, Southern Utah; The Great Salt Lake of Utah.

testing required in an Alkali Works. State salary required -Address, M. N., CHEMICAL NEWS Office, Boy Court, Ludgate Hill London, E.C.

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Repulsion Resulting from Radiation.


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requires some care. It should be drawn from flint glass, NEWS, as this gives much tougher threads than foreign glass.



(Continued from p. 220).

IOI. THE difficulty which attended experiments with the
balances and bulb apparatus used at first was to bring the
moving part accurately back to zero, and also to measure
the deflection produced. I therefore tried several plans of
giving a fixed zero-direction to the movable index. Thus
a piece of magnetic oxide of iron was cemented to one
end of the index, and a permanent magnet was brought
near it. This answered pretty well, but was inconvenient,
besides not being sufficiently accurate. A bifilar suspen-
sion from cocoon-fibres seemed likely to succeed better;
but the difficulty of suspending the rod in this manner, so
as to get exactly the same tension on each fibre, was very
great, and unless this was done there was more tendency
to move in one direction than in the other. When I had
succeeded in suspending the needle with an equal tension
on each silk fibre, I found their elasticity to vary; and as
soon as the vacuum was approached one was sure to con-
tract more than the other, twisting the needle out of the
axis of the tube, and sometimes causing it to touch the
side. This method of suspension was therefore abandoned.
By increasing the length of the needle, and also of the
fibre used to suspend it, it was possible to employ fibres
with a considerable amount of torsion, and still preserve
the delicacy of the apparatus. Fine platinum wire was
first tried; but this was soon abandoned in favour of glass
fibres, which were found to answer so perfectly that I have
since used nothing else.

The diameter varies with the amount of torsion required;
it may be o'o01 inch or less. I select the piece best
adapted for the special experiment in the following
way: Several threads of glass are first drawn out before
the blowpipe, and a certain number selected as being
likely to answer the purpose. These are then suspended
side by side to a horizontal rod and equalised as to
length. A piece of glass rod, about 2 inches long, which
is always kept for this purpose, is then cemented by
shellac on to the end of one of the threads. Air currents
are then cut off by a glass screen, and the thread being
set in movement by a slight twist, the torsion is measured
by timing the oscillations. This having been done with
each thread in succession, one is selected and mounted
in the apparatus. If it works properly, well and good;
if not, it is easy to select a thread having the requisite
amount of torsion, more or less, and substitute it for the
one first used.
FIG. 6.

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In fitting up one of these apparatus threads were drawn out which were found to require, respectively :

102. Fig. 7 shows the form of apparatus which I have finally adopted, as combining the greatest delicacy with facility of obtaining accurate observations, and therefore of getting quantitative as well as qualitative results. It a is a torsion apparatus in which the beam moves in a horizontal plane, and may be called a horizontal torsion balance. a b is a piece of thin glass tubing, sealed off at the end b and ground perfectly flat at the end a. In the centre a circular hole, c, is blown, and another one, c', at the end; the edges of these holes are ground quite fiat. a, c, and c' can therefore be sealed up by cementing flat transparent pieces of plate glass, quartz, or rock-salt, a, d, and d' on to them (83). To the centre of a b an upright tube, e f, is sealed, having an arm, g, blown on to it for the purpose of attaching the apparatus to the hi is a glass index, drawn from circular or pump. square (22) glass tube, and as light as possible consistent with the needful strength. A long piece of this tube is first drawn out before the blowpipe; and it is then calibrated with mercury until a piece is found having the same bore throughout: the necessary length is then cut from this portion. jk is a very fine glass fibre, cemented at j to a piece of glass rod, and terminating at k with a stirrup, cut from aluminium foil, in which the glass index, hi, rests. In front of the stirrup is a thin glass mirror, shown at k, silvered by Liebig's process, and either plane or concave as most convenient. At the ends of the glass index (h i) may be cemented any substance with which it is desired to experiment; for general observations I prefer to have these extremities of pith, as thin as possible, and exposing a surface of 10 millimetres square. The pith may be coated with lampblack or silver, or may retain its natural surface.

103. The preparation of the suspending thread of glass


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for a half oscillation when the glass weight was hung on to their ends. The one oscillating in 30 seconds was first used, but was found to give insufficient torsion. The one making half an oscillation in 11 seconds was then used, and was found to answer well. Before I adopted this plan days were frequently wasted in the attempt to hit upon a glass thread of the requisite degree of fineness. 104. In taking accurate observations with an apparatus of this description, it is necessary to support it on a stand firmly fastened to a main wall. When resting on a bench, or connected in any other way to the floor, there is a constant oscillation which keeps the index from zero.

The apparatus being fastened firmly to its stand, accurately levelled, and sealed on to the pump, a divided scale, a b (fig. 8), is placed four feet from the small mirror; and immediately beneath the scale is a narrow brass slit,


New Process for Titrating Astringent Substances.

CHEMICAL NEWS, Dec. 1, 1876.

c, illuminated by a lamp, d. In front is a lens, e, which | for some weeks, as the residual moisture in the pithw throws the image of the slit on to the mirror, where it is then have been absorbed by the sulphuric acid in the reflected back again on to the divided scale. Here the pump. angular movement of the bright line of light shows the (To be continued.)

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minutest attractive or repulsive force acting on the pith at the extremity of the movable index.

In order to keep the luminous index accurately at zero, except when experiments are being tried, extreme precautions must be taken to keep all extraneous radiation from acting on the apparatus. A slightly conical paper tube, f, about 6 inches long, and as narrow as the angular movement of the ray of light will admit of, is cemented on to the glass window in front of the mirror; and a similar tube, g, is cemented on to the quartz window in front of the pith surface on which radiation is to act. The latter tube is furnished with card shutters, h, i, at each end, capable of easy movement up and down. The whole apparatus is then closely packed on all sides with a layer of cotton-wool, about 6 inches thick, and outside this is arranged a double row of Winchester quart bottles, j, j, filled with water and covered with brown paper, spaces being only left in front of the paper tubes. k and 1 represent the positions of the candle 140 and 280 millims. distant from the pith. The whole arrangement has the appearance shown in fig. 8.

105. I will not discuss at present the phenomena presented when the apparatus is full of air, or when the vacuum is imperfect, but will proceed to the effects observed when the exhaustion has been pushed to the highest attainable degree. However much the results may vary when the vacuum is imperfect, or when the apparatus is full of air, I always find them agree amongst themselves when the residual gas is reduced to the minimum possible; and I have also ascertained that it is of no consequence what this residual gas is. Thus I have started with the apparatus filled with various vapours and gases, such as air, carbonic acid, water, iodine, hydrogen, or ammonia; and at the highest rarefaction I find no difference in the results which can be traced to the residual vapour, assuming any to be present. A hydrogen vacuum seems neither more nor less favourable to the phenomena than does a water or an iodine vacuum. If moisture be present to begin with, it is necessary to allow the vapour to be absorbed by the sulphuric acid of the pump, and to continue the exhaustion with repeated warming of the apparatus until the aqueous vapour is removed; then only do I get the best results. When pith surfaces are used at the extremities of the glass beam, they should be perfectly dry; and they are more sensitive if the apparatus has held a vacuum



WHEN we pour drop by drop a solution of iodine into any decoction of an astringent matter, previously mixed with an alkaline carbonate, we remark that this solution is absorbed with a great energy. I have observed that the absorption of the iodine takes place, in these conditions, in the direct ratio of the quantity of astringent matter taken, and that I part by weight of tannic acid absorbs 4 parts of iodine before we can observe the presence of free iodine in the liquid. It is on this action of iodine on astringent matters that the process of titration is based which forms the subject of this note. The solution of iodine necessary for titrating tannin is obtained by dissolving in iodide of potassium 4 grms. of iodine, and adding to the solution distilled water in quantity sufficient to make a volume of 1000 c.c. To ascertain the value of the solution of iodine, we introduce into a beaker Io c.c. of a solution of tannin at o'i grm. per cent; we mix it with 2 c.c. of an alkaline lye containing 25 per cent of crystallised carbonate of soda; then, by the aid of a graduated burette, we cause to fall into the alkaline liquid the solution of iodine until a drop of the mixture, taken with the glass stirrer and put on a leaf of starched paper, produces a light violet spot, which indicates the presence of free iodine and the end of the operation. The value thus obtained must be corrected, that is to say we must deduct from the number of cubic centimetres of the solution of iodine corresponding to o'or grm. of tannin, the volume of this solution, which it is necessary to employ as pure loss before obtaining a coloured reaction on starched paper. For this purpose we measure 10 c.c. of distilled water, which is mixed with 2 c.c. of the alkaline solution; then we pour drop by drop the solution of iodine until we obtain a spot on the starched paper. With a solution of iodine, containing 4 grms. iodine per litre, the correction is commonly from o'I c.c., but the greater or less purity of the carbonate of soda may perhaps affect this correction very slightly. For o'oi grm. of tannic acid dissolved in 10 c.c. of water we must generally use 10'5 c.c. of the solution of iodine at 4 per thousand. Under the influence of iodine the alkaline solutions of tannin, even diluted, take a colouration so intense that it


Dec. 1, 1876.

Estimation of Potassium as Acid Tartrate.

would not be possible to seize distinctly the colouration of | iodide of starch if we added starch paste to the tanniferous liquid. This is why I have recourse to a leaf of white filter paper, which I cover by friction with a slight layer of powdered starch. The spots made on this paper with half a drop of liquor containing traces of free iodine are immediately absorbed and show the characteristic violet colouration, even when the liquid is deeply coloured. When the value of the solution of iodine is established with respect to a known weight of pure tannic acid, this test liquor may be employed to titrate the various astringent matters, if we adopt, as the authors of the processes for the determination of tannin hitherto published have done, tannic acid as the type of the active principle of astringent matters. But, if we wish to make very exact researches, it is necessary for each variety of astringent matter to be studied to ascertain the value of the solution of iodine by means of the pure astringent principle; for example, catechuic acid for catechu-moritannic acid for fustic; for the solution of iodine acts, without doubt, like other reagents in different proportion upon divers tannic acids. The tannic acid which I employ to establish the value of the solution of iodine is obtained by keeping the tannin of Pelouze at 80° in the water-bath. At this temperature a portion of tannin, about 42 per cent, melts, agglomerates into a greyish spongy mass, which contains the impurities of the tannin with the resins; the pulverulent part constitutes pure tannin and 105 c.c. of the solution of iodine at 4 per thousand correspond to oor grm. of this tannin, whilst only 93 of the solution of iodine are required to saturate oor grm. of the gummy matter. The titration of tannin by means of the solution of iodine being very rapid and very exact, I determined to apply it to the assay of natural astringent matters. For this purpose I had to ascertain whether the matters which accompany the tannin in vegetable extracts are without action on the solution of iodine. For this purpose I exhausted with 100 c.c. of distilled water 1.515 grms. of oak bark, which, assayed according to Honer's process, contained 65 per cent of matter fixable by hide, and I performed in to c.c. of this decoction, containing consequently o'or grm. of tannin matters, the titration with a solution of iodine of which 105 c.c. corresponded to o'or grm. of pure tannic acid. If the extractive matters which accompany the tannin had acted on the solution of iodine I should have had to employ more than 10'5 c.c. of this solution; but in three assays I obtained the coloured reaction on starched paper. After having poured 9.8 c.c. of the solutions of iodine, I found then 5'92 c.c. per cent of tannin instead of 6'5 c.c., the value found in using Hammer's process. The discrepancy of o'58, which the two processes give, must be attributed to the colouring matters which have been fixed by the hide along with the tannin in the assay by Hammer's process. In a second experiment I treated the same decoction of oak bark with an excess of powdered hide, and having separated by filtration the hide charged with tannin, I obtained, with 10 c.c. of the filtered decoctions, the reaction upon the starched paper after having employed 17 c.c. of the solution of iodine; whilst before the action of the hide it would be necessary to employ 9.8 c.c. But these 17 c.c. of solution of iodine, corresponded to 102 per cent of gallic acid, the average quantity of this acid, which has been remarked in French barks. Finally a decoction of oak bark was precipitated by acetate of copper. The tannate and the gallate of copper were separated by filtration, the filtered liquid was neutralised by carbonate of soda, then filtered anew to separate carbonate of copper. 10 c.c. of the clear solution, after an addition of 2 c.c. of a lye of carbonate of soda, only required o'r c.c. of the solution of iodine to produce a coloured reaction upon starch. This result shows very clearly that the ex. tractive matters do not act on the solution of iodine, since we have only employed of this solution the volume which would have been necessary if we had operated upon distilled water, and nevertheless the liquor separated from


the gallate and the tannate of copper contained all the extractive matters, save a small quantity of brown acids which the acetate of copper had precipitated. Having shown that in the decoction of oak bark it is only tannic and gallic acids that absorb the solution of iodine, the process of titration that I propose may be employed with all safety for the assay of tanniferous matters. I have found that crystallised gallic acid decomposes the solution of iodine exactly in the same ratio as tannic acid. If then we wish to determine separately the gallic and tannic acid, we must determine at first the volume of the solution of iodine corresponding to the two acids jointly; then, after having separated the tannic acid by powdered hide, titrate the gallic acid remaining in solution. On deducting from the volume of the solution of iodine corresponding to the two acids that which belongs to gallic acid alone, we obtain the quantity of tannic acid.-Bulletin de la Société Chimique de Paris.




IN most cases which present themselves to the chemist,
in which potassium is to be estimated, it is accompanied
by sodium, and the course usually pursued is to estimate
the potassium directly as platino-potassic chloride. The
precipitate obtained has the advantage that its weight is
very great when compared to the weight of potassium in
combination. There are difficulties, however, connected
with the process, and there are cases in which it is not
applicable without elaborate preparation; but platinic
chloride, although expensive, is an excellent reagent, and,
its use.
in experienced hands, very good results are obtained by

Indirect processes are also in use, one of which consists in combining potassium and sodium with either chlorine or sulphuric acid, and in estimating the total quantity of salts by one operation and the quantity of either chlorine or sulphuric acid by another operation. From these two quantities the potassium and sodium can be calculated. Very good results are also obtained by this process.

There is also a very curious indirect process due to Gay-Lussac, to which I call your attention because I believe that it is not generally known, and because it presents a singular example of the expedients to which chemists have resorted to estimate potassium in presence of sodium. This process, which was in use some years ago in French saltpetre works, and may still be in use, is based on the following facts:-When 50 grms. of pure chloride of potassium are dissolved in 200 c.c. of water, the temperature of the liquid falls 114° C. If we take 50 grms. of chloride of sodium the fall of temperature will be only 1.9° C. Gay-Lussac has directed that the glass vessel in which the solution takes place should weigh 185 grms.-a point of some importance, as the vessel must acquire the temperature of the liquid it contains. To test a mixture of potassium and sodium salts they are brought, in the first place, to the state of chlorides and dried, and 50 grms. of the mixture are taken and dissolved in 200 c.c. of water. A decrease of temperature is noted, and the proportions of potassium and sodium chlorides are obtained from a table in which these proportions are placed, opposite numbers indicating the decrease of temperature. If this table is not at hand, the quantity of potassium chloride in 100 parts of the mixture may be found by calling the percentage of chloride of potassium x, and the decrease of temperature, in degrees C., d. Then 100-x will be the percentage of sodium chloride, and we shall have

* Read before the American Chemical Society, September 7, 1876.

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