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But to distinguish the false from the real is not always so easy, as the following story, which we will quote for the amusement of our readers, will show :

“A noble lady in this country formerly possessed one (a sapphire), which is, perhaps, the finest known. The lady, however, sold it during her lifetime, and replaced it by an imitation so skilfully made as to deceive even the jeweller who valued it for probate duty; and it was estimated at the value of 10,000l., and the legacy duty paid on it by the legatee, who was doubtless chagrined when he discovered the deception." We should think he was; and it may moderate the transports of some who see gorgeous displays of jewellery to be informed that a handsomely printed circular in our possession informs ladies who have occasion to part with their jewels for a time that imitations which defy detection will be supplied at a certain establishment on short notice, adding that "perfect confidence and the utmost secrecy may be relied on." But it is time that we betook ourselves to the scientific contents of this book. We may pass over the chapters "On the Ideas of the Ancients Respecting Precious Gems," and "On the Precious Stones Mentioned in the Bible,' which will have great interest for the general reader, and

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come at once to the account of the diamond, which is, as it ought to be, one of the best in the book. In this we in chemical books; it is here called "carbonate, or diamond carbon." It is found in the province of Bahia, and occurs in sandstone apparently of the same era as the gneiss and syenite rocks of Norway and Greenland. "Its hardness is identical with that of the diamond, and its specific gravity from 3012 to 3416; some specimens show an imperfect crystalline structure of a brownish-green, opaque colour; others of a granular structure, porous enough to resemble pumice-stone, dense, very massive, and found sometimes in lumps as large as a walnut. It is extremely hard, in some cases taking a polish equal to diamond, and appears to be carbon imperfectly crystallised; when burnt, it leaves a residue of clay and some other substances. This substance would appear to be the connectinglink between uncrystallised carbon and the diamond, and a scientific examination of it might lead to important results."

find mentioned a form of the diamond which is not described

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There would appear to be another uncrystallised form of the diamond known as "Boart." Both this and the former are crushed to powder, and used for cutting and polishing other diamonds, rubies, &c.

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The account of the method of splitting, cutting, and polishing diamonds is very good; and here we meet with a description of the "brilliant,' the fashionable form of the present day. "The general form of the rough diamond is of two pyramids joined at the base; if a diamond is not of this form it must be made so by art; and in order to produce the table there must be taken away from the upper pyramid five-eighteenths, and from the lower oneeighteenth of the total thickness. The upper or flat part is called the table, and from thence to the girdle or centre edge and broadest part of the stone are facets, called star facets; from the girdle to the lower or pointed part, called the culet, and which is nearly pointed, are facets, called skill facets. These facets meet in the middle of each side of the table and girdle, and also at the corners, forming regular lozenges on the four upper sides or corners of the stone. The triangular facets on the under side of the culet to the girdle must be half as deep again as the upper or star facets. The thickness of the stone should be in this proportion :-From the table to the girdle, one-third; and the girdle to the culet, two-thirds of the total thickness; the diameter of the table, four-ninths of that of the girdle; the culet one-fifth of the table. The girdle of the stone should be of the same dimensions as the thickness or depth. A stone, if well cut, should have a very thin edge at the girdle; and any overweight or substance retained

to make a diamond heavier only detracts from its play or beauty."

A stone so cut and proportioned, and free from flaws, will at the present day, if of one carat ( = 4 grains), be worth 18.; but if of five carats weight it will fetch 320l. In 1750 a diamond of five carats would, according to Jeffrey, "The value of stones above five have been worth 200l. carats is not attempted to be given, as it is impossible to fix it with accuracy, this depending entirely on the demand for any particular size and the supply in the market." Rose-cut stones fetch at the present day rather less than brilliants.

Of the other precious stones we need not speak. The chemistry of them will be well known to our readers, but they will find much interesting matter relating to them in

Mr. Emanuel's book.

In an appendix to the book the reader will find a tolerably complete list of works relating to gems; but we notice that neither here nor in the body of the book has the author referred to the experiments of Ebelmen, Deville, Troost, and others, on the artificial formation of precious stones. This may be politic in a jeweller, since the writers referred to suggest a day not far distant, when, at all events, rubies, sapphires, and amethysts may be produced at will. The day pleasantly imagined by Alphonse Karr, when a philosopher shall exhibit at the Academy of Sciences a diamond as big as his fist, and apologise for the smallness of the specimen, may still be distant, but nearer, perhaps, than is generally supposed.

CORRESPONDENCE.

Continental Science.

PARIS, August 26. In the absence of any chemical or technical information worth notice, nothing, perhaps, will have more interest for the readers of the CHEMICAL NEWS than an account of the various remedies for the cholera which the fear of an

approaching outbreak has brought to notice. It will be unnecessary to preface the mention of these with any remarks on their probable efficiency. They come before the world stamped with the authority of their writers, medical men, who profess, in each instance, to have proved the value of the remedy recommended, and it will be for your medical readers to decide whether they will put the remedies to the test or leave their patients to Providence.

The first I may mention is that which Dr. Ponowski, of St. Petersburg, has published. It is powdered hellebore, veratrum album, I suppose taken by the nose, like snuff. This is an infallible remedy when the patient sneezes eight or ten times after a pinch; but if the patient does not sneeze his case is altogether hopeless.

The next thing I may mention is much more valuable, since a preventative is better than a cure. Dr. Burq has noticed that workmen employed on copper are never attacked with cholera, and he accordingly suggests the employment of this metal as a prophylactic against, and as a remedy in case of an attack. With the first object, he applies the metal externally, in the form of a girdle constructed of thin plates of copper, fixed at short intervals on an elastic band, so that they may be easily fixed round the body. The metal must of course be in contact with the skin, and the Doctor leaves it there until a considerable amount of verdigris is formed, which must not be disturbed; hence, he says, the wearer must bathe as little as possible. A copper bandage, however, is troublesome, and sometimes, Dr. Burq says, brings out an eruption, and even causes sickness. Should either happen the bandage may be discontinued and an ointment of verdigris, extract of belladonna, and lard, rubbed under the armpits and inside the thighs every night; or, instead of

this, bathing in a solution of sulphate of copper every other day might do. Besides using this girdle, it will be well to imbibe once a day, or even twice if the epidemic is very prevalent, small doses of acetate of copper, with a little opium. In case of an attack, the author would use all these methods together, and lavements of sulphate of copper as well.

Another remedy suggested is carbonic acid, which is to be injected into the veins.

A fourth writer, whose name also escapes me, has written to recommend frictional electricity. He would insulate the patient, and take sparks all down the spine and from the pit of the stomach.

Lastly, M. Surviron proposes to destroy at once the means of infection by producing ozone continuously on a large scale; but the Academy has been wicked enough to keep the author's method of getting ozone on a large

scale to themselves.

MISCELLANEOUS.

British Association. It is hardly necessary to remind our readers that the annual meeting at Birmingham commences on the 6th of this month. The chemical section will meet in the English School, King Edward's School-President: Professor W. A. Miller, M.D., F.R.S., &c.; Secretaries: A. Vernon Harcourt, Esq., M.A., F.C.S.; Professor Wanklyn, F.C.S.; H. Adkins, Esq.; and A. Winkler Wills, Esq. We shall give full reports of the proceedings of this section. Authors wishing their papers to be published at length are requested to forward them as early as possible.

British Pharmaceutical Conference.-The meeting for the present year will be held at Birmingham, at the Odd Fellows' Hall, Temple Street. It will commence on Tuesday, the 5th September, at 10 a.m., and be continued on Wednesday, the 6th, at the same hour, and on Thursday and Friday, 7th and 8th September, at seven o'clock in the evening. Many interesting papers on Pharmaceutical subjects are already promised, and others will, doubtless, be sent in. A large gathering of members is expected.

A Rival for the Magnesium Light.—Mr. Jas. Wilkinson, of Chelsea, has invented a composition of phosphorus, nitrate of potash, and "five other powders," which, when burnt, gives a light sufficiently bright to produce very sharp photographic pictures.

Telluride of Copper.-We must add to our report of M. Becquerel's memoir, at page 57, the remark of the author that telluride of copper is a much more powerful thermo-electric element than sulphide of copper.

Agglutinative Tissue.-Dr. Fort (Rep. de Pharm.) suggests as a substitute for the English isinglass plaster, a tissue made as follows:-Take of gum arabic, selected, 5 drachms; distilled water, drachms; glycerin, a suffi cient quantity. Dissolve the gum in the water, and add sufficient glycerin to render the mucilage of the consistence of syrup. This solution is spread by means of a brush on one side of thin glazed muslin. The author suggests this plaster as inodorous, very supple, and as not cracking in winter, owing to the glycerin in its composition. It adheres strongly by simply moistening the surface, and can be easily removed. The author does not say whether it is hygroscopic, or ill adapted for a damp atmosphere.-Am. Jour. of Pharm.

Accidental Poisoning.-Mr. Noakes, a highly respectable chemist at Brighton, has been committed to take his trial for causing the death of a customer by dispensing tincture of aconite instead of tincture of henbane. If there can be any consolation under such circumstances, it might be found in the circumstance that the victim in

this case was a gentleman, aged 81, suffering from a disease which was likely to terminate his life naturally in the course of a few days. It is worthy of remark that the mistake was made by the principal of the establishment, a man of very high character, and who could not be supposed to be insensible to his own interests, and not by an assistant or apprentice. Upon this matter we may quote with approval the following remarks from the Standard:-"There is no more serious matter for contemplation than medical 'poisoning by mistake,' for if the lives of the sick and the infirm are at the disposal of one person more than another, that person is the chemist and druggist. The physician prescribes, but the chemist compounds; and so great is the confidence of patients and their friends in his skill and businesslike correctness, that the drug or the mixture is swallowed fearlessly, and with only the wry face that is as natural to medicine taking as a long face is said to be to grief. Most of us are, at one time or another, in the hands of the skilled tradesman with the bottles of tinted glass and the illuminated and mysterious diploma in his window, and when the phial comes from his shop we drink from it in perfect reliance on the compound being correctly made up,' and those minute quantities represented by grains and scruples being just to a particle. It is, indeed, upon this strong confidence placed in him, his education, and his diploma, that the druggist exists as the middleman between the doctor and the patient. He may know nothing of the ailment his drugs are expected to alleviate, nor of the disease they may be asked to cure. He has before him the cabalistic signs, the abbreviated dog Latin of the profession, and he silently obeys the cabala with a neatness of hand and a general coolness of aspect peculiar to the calmn and strangelyperfumed region in which his business is transacted. Habit, perhaps, makes the druggist a trifle too cool and confident in some cases. He appears to know his jars and bottles by the touch, just as the compositor mechanically selects from the frame before him the right letter and puts it in the right place with what ordinary observers look upon as comparative inattention. With the apothecary's weights and measures the same cool certainty appears to prevail, and when the phial being filled or the pills made up he neatly envelopes the bottle or the box in fair white paper, seals it, and passes it over the counter, it often occurs to the recipient what a clean, steady, firm-handed gentleman the chemist and druggist is, and how well he answers to the great trust reposed in him. Not unfrequently he has to make up something from oral instruction, or even from the lights afforded him by an old inscription on a confidence in his handling of the drugs, and with the inphial. And this he does with the same neatness, the same

it be considered that this apothecary has life or death in variable characteristic cleanliness of his craft. Now, let the reach of the criminal law, and that very often he has his hands, that a slip or a mistake may bring him within to decipher handwriting that would astonish the blind clerk at the General Post-office; and it will be admitted chemist and druggist." that, on the whole, the invalid public is served well by the

ANSWERS TO CORRESPONDENTS.

W.-We do not remember one, but will make inquiries.
J. H.-We will keep the subject in mind.

J. C. F-Decomposing lead soap (diachylon plaster) with carbonate of soda will give you a very pure oleate of soda.

N.-The French grain is less than the English. One gramme = 18.83 French grains.

J. B., Devon.-The application can do no harm. It is recommended in cases where the cause of baldness is supposed to be parasitic growth around the roots of the hair.

G. G. or 99.-We must thank our correspondent again for his communication. As he states, some are not errors, and most are un'inportant. If the corrections were forwarded weekly, we could give a list of errata.

NEWS

SCIENTIFIC AND ANALYTICAL
CHEMISTRY.

New Method of Estimating Sulphides,
by M. VERSTRAET.*

THE estimation of alkaline sulphides is most important
in very many industrial and commercial operations.
In the manufacture of carbonate of soda by Leblanc's
process, an exact knowledge of the quantity of sulphides
contained in the different operations is required every
instant in the direction of the work; for the quality and
whiteness of the salts almost always depend on the
amount of sulphides contained in the rough soda, or
which is formed during the lixiviation, under the
influence of the temperature, and the contact of the
soda with the solvent. An exact knowledge of the
amount of sulphides is'in this case absolutely necessary.
In the estimation of sulphides one of the indispensable
conditions is that the process must be simple, easy, and
rapid, and, above all, readily intelligible to the super-
intendents, all works not having experienced chemists
at their disposal.

Several methods have already been proposed; M. Lestelle's is the most rapid, which estimates the sulphides by ammoniacal nitrate of silver in the presence of enough NH, to retain in solution all the salts of silver except the sulphides. This process, however, although quick and easy, has its inconveniences.

We have endeavoured to avoid these inconveniences by a process which we believe may be employed by any foreman or intelligent workman, and we hope that our expectations have been realised.

In the preparation of the standard solution, we substitute copper for silver. The quantity of copper required in the estimation of the sulphide will evidently vary according to the nature of the sulphide to be operated on. But suppose the question turns upon the estimation of sulphide of sodium.

As M. Pelouze has shown in an account of his simple and accurate method of estimating copper by a solution of sulphide of sodium, the sulphide of copper produced by the double decomposition which takes place when a solution of sulphide of sodium reacts upon another solution of ammoniacal nitrate of copper, at a temperature varying from 50° to 90°, is not the sulphide CuS, corresponding to the monosulphide of sodium NaS, but an oxysulphide CuO,5Cus. To obtain an exact estimation, it is, then, necessary always to operate at a temperature varying from 50 to 85°; this result may be easily obtained, even during the boiling of the liquids, by occasionally replacing the ammonia which is driven off. If the liquid is always ammoniacal, the temperature will not rise beyond 75°, as may be easily verified by plunging the thermometer once or twice into the liquid. Before preparing the standard solution, care must be taken to ascertain that the materials to be used in its composition be free from impurity. The standard solution is prepared by dissolving 9'737 gr. of copper in about 40 grammes of nitric acid. The solution freed by the boiling from the hyponitric acid is mixed with from 180 to 200 grammes of ammonia, and water is then added so as to obtain a litre of liquid.

making a solution of nitrate of copper react while hot upon a solution of sulphide of sodium, ought to have no action upon a small quantity of ammoniacal nitrate of copper; decolouration would show the presence of other metals in the copper.

Assay of Matter containing Sulphide of Sodium. ment must necessarily vary according to the amount of -The quantity of material convenient for the experisulphide which it contains, and to obtain a strict estimaamount of solution contains not more than from o'ro gr. tion, the quantity should, if possible, be such that a given to o'20 gr. of sulphide.

rough soda. We take for the experiment 10 grammes Suppose we take the determination of sulphide in of soda, which must be roughly pulverised and treated by 250 cubic centimetres of water; leave it to digest about of soluble matters. It must be filtered to separate the an hour, agitating it at times, to accelerate the solution insoluble residuum, and 50 cubic centimetres of the filtered liquid, representing 2 grammes of the rough soda, must be taken for the experiment.

Introduce these 50 cubic centimetres of solution into a small flask about 150 cubic centimetres in capacity, and heat the flask over a spirit lamp until it boils, which, on add from 25 to 30 grammes of pure ammonia. Then account of the ammonia, will be between 50° and 60. Then add to the boiling solution, by the aid of a burette graduated and divided into tenths of a cubic centimetre, the standard solution of ammoniacal nitrate of copper. Agitate and boil from time to time, in order to facilitate the collecting of the deposit of the oxysulphide of copper. Towards the close of the operation add the standard solution, drop by drop, heating after each addition. Light shadows may then be perceived, at first black, afterwards yellowish, which rise from the bottom of the flask, and spread over the whole liquid. As we near the end of the experiments, these shadows become lighter and less coloured, on account of the smaller quantity of sulphide of copper which they contain. As soon as these little shadows have completely disappeared, the solution, under the influence of a drop of standard solution of copper, takes a light blue tint. This is a sign of the completion of the experiment. The next thing is merely to read off the burette the number of divisions of standard solution employed, to know exactly the quantity of sulphide contained in the rough soda. Suppose it near 6.5 cc.; as each cubic centimetre represents o'or gr. of timetres of solution of soda, representing 2 grammes of pure, dry monosulphide the 6.5 cc., or the 50 cubic cenmatter, contain 0.065 gr. of sulphide, equivalent to 3:25 per cent. Good sodas never contain more than from o'z to 0'4 of sulphide.

The experiment, we may easily see, is just completed, for after the addition of the first portion of the standard solution, the liquid took a dirty green colour, and remained turbid, because of the suspension of precipitated oxysulphide of copper clears immediately; the sulphide is flask in light black flakes. more easily deposited, and collects at the bottom of the

With a little practice, exceedingly minute quantities. of sulphide may be easily detected, even down to about o'00 gr. An experiment requires about ten minutes.

Still more to accelerate and simplify the process, we have prepared a standard solution of sulphide of sodium, in such a way that a litre of this second solution exactly pre-saturates a litre of standard solution of copper. In this manner if, in any assay of sulphide of sodium, one has gone beyond the stage of precipitation by adding too much copper solution, it is always easy to return to the

The copper should be exempt from other metals; it should dissolve completely in nitric acid, give no cipitate with ammonia, and, as M. Pelouze has shown, the precipitated oxysulphide CuO,5CuS, formed by

* Comptes Rendus.

VOL. XII. No. 301.-SEPTEMBER 8, 1865.

exact determination, and to correct the experiment, without re-commencing it.

Testing of Sulphide of Potassium.-Sulphide of potassium is estimated in the same way as sulphide of sodium. But instead of using in the preparation of the standard solution of copper 9737 gr. of pure copper, only 6.880 gr. should be employed.

On a Process of Fractional Condensation, applicable to the Separation of Bodies having small Differences between their Boiling Points, by C. M. WARREN.

(Continued from page 100.)

Having described the apparatus, I now proceed to give such details of the method of conducting the separations as have been found, in my experience, most efficient and economical of time. In commencing with a crude mixture of unknown liquids, I deem it advisable to operate at once on a tolerably large quantity of material, especially if the constituents are supposed to be numerous, and to omit chemical treatment till after the separations have so far progressed as to indicate the number and species of bodies present, and, approximately, their several boiling-points.

Notwithstanding the precautions taken to avoid loss from evaporation and leakage, I have at times been surprised at the large waste of material which has been made apparent after a long series of operations. When it is considered, however, that the time required to make a complete separation of a very complex mixture of liquids must necessarily be very protracted, during which more or less of evaporation is constantly taking place, it will be a matter of no surprise that the loss is so considerable. The quantity of material required must depend also on the proportions in which the various constituents are contained in the crude mixture, and upon their degree of volatility; but as these cannot be known a priori, it may suffice to make a single preliminary distillation of a portion of the mixture from a tabulated retort, to ascertain the range of temperature within which it distils, noting at the same time the proportions which come over between certain temperatures-as, for example, below 50° C., between 50° and 100°, &c. From these data one may judge pretty nearly of the quantity which it will be advisable to take. It is evident that when very volatile bodies are present, even in considerable proportion, a much larger quantity would be required than if the material were but slightly volatile, as the waste in the former case from evaporation would be much greater.

But in many cases it will be found that highly volatile bodies are present only in very small proportion-e.g., in viscid petroleums like Rangoon tar, and in the products of distillation of some species of asphalt. In such cases, the requisite quantity to be operated upon to obtain the most volatile constituents in sufficient quantity for anything like a complete study of their chemical relations would be extremely large-too large to be conducted in the laboratory-and one would have to resort to the manufactory for the first distillation. I have dwelt at some length on this point, having experienced the disappointment which one feels, after months of labour, on finding the products insufficient for his requirements, when the expenditure of a little more time, comparatively, might have given double the quantities obtained. In the first series of fractioning I generally operate on successive portions of about one gallon each of the crude material, and take off a fraction for every 20° C. rise of temperature of the retort. These fractions are

preserved in well-stoppered bottles, and each carefully labelled with the temperatures between which it was obtained. The fractions for each fresh portion of the crude material being collected between the same limits of temperature, are added to the corresponding products from the preceding operations till enough of the crude material has been taken to insure ultimately a sufficiency of the pure products.

sequent fractionings, when the temperature to which the In the commencement, not only of this but of all subbath should be raised is unknown, I first bring the liquid in the retort into full ebullition, so that a steady stream of liquid should flow back from the end of the worm into the retort. I then carefully raise the temperature of the bath until the vapours from the retort pass through the heated worm so freely that the liquid, in condensing from them, shall drop with tolerable rapidity into the cold receiver. In order that this dropping may be continuous, it is necessary that the temperature of the bath should rise very gradually as the more volatile constituents of the mixture are taken off. This is easily effected by carefully regulating the flame under the bath. It is advisable to boil the retort as rapidly as possible without choking the lower end of the heated worm with the returning liquid. As this choking would give rise to additional pressure in the retort, and consequently occasion abnormal elevation of the temperature, and possibly a rush of liquid into the receiver, and thus introduce irregularities in the work, excessive heat under the retort should be avoided. The first indication of choking of the worm is a partial or entire stoppage of the stream of liquid which normally flows steadily from the end of the worm into the retort. Any interruption or unsteadiness of this flow would indicate too rapid ebullition. As a rule, other things being equal, the greater the difference between the temperature of the bath and that of the retort, the slower the products will come off, and the more effectual will be the separation. I think it possible, however, that the earlier fractionings may be conducted so slowly that the loss of time would more than counterbalance what might be gained by more thorough separation, and that equally good results may be more economically obtained by more frequent operations, somewhat more rapidly conducted.

A striking illustration of the advantage to be gained by this process is presented by the fact that, during the first fractioning of a crude mixture, such as American petroleum or coal-tar naphtha, for example, the difference between the temperature of the bath and that of the retort may sometimes be as much as 35° C., or even more; while, as the products become purer, this difference between the temperatures of the bath and retort proportionally decreases, till finally, in operating on a pure product, the temperature of the bath must be brought to within a few degrees of that of the retort, in order to bring the vapours through. But the amount of this difference is variable for different bodies of equal purity.

These first fractionings must necessarily be quite arbitrary, for, as a general rule, when operating on such mixtures as those just mentioned, neither the thermometer nor the quantities obtained for any given range of temperature will indicate any decided preponderance of any one substance. On the contrary, the temperature rises uniformly, and about the same quantity is generally obtained for the same number of degrees of temperature throughout the operation. In other mixtures, in which certain bodies may seem to be present in much larger proportion than others, or in which there may be a

CHEMICAL NEWS,
Sept. 8, 1865.

Cause of the Solidification of Balsam of Copaiba by Lime, &c.

greater difference between the boiling points of the con-
stituents than in the cases referred to-facts which
would be indicated by the thermometer of the retort and
by the relative quantities of the products obtained
there might be something gained by exercising discretion
in taking off fractions according to these indications.
In the second series of fractioning, the first or lowest
fraction of the preceding series, which is large enough
to operate upon by itself, is transferred to the retort,
and brought into ebullition. The temperature of the
bath is then adjusted as above described, and the distil-
lation continued, the fractions obtained being placed in
their appropriate bottles until the temperature of the
retort shall have risen to, or somewhat above, the point
at which the second or next succeeding fraction of the
first series may be supposed, or has been found by ex-
periment, to boil. This fraction is then added to the
residue in the retort, and the distillation is continued as
before. In the same manner, I proceed with the remain-
ing fractions of the first series.

III

be suspended, provided the pure products already obtained should be large enough for the purposes required. But, in my investigations, I have undertaken to prove the negative as well as the positive. I have attempted to carry the process of separation so far that I might assert the absence of other bodies as well as the presence of those obtained; and this clearing up of the intermediate fractions has generally been the most tedious part of the work. I have continued to operate upon these by themselves, until they also have become distributed in regular course-no new bodies appearingamong the fractions of constant boiling point, or to such an extent that the intermediate quantities have become too small to admit of further continuance of the process. This process has been in constant use in my laboratory during the last three years. In this time it has been applied in the study of petroleums, coal oils, the more volatile parts of coal and wood tars, the essential oil of cumin, commercial fusel oil, from corn whiskey, and even to mixtures more complex than either of these. As All subsequent fractionings are similarly conducted. the result of this long experience, I can say that, as As the work progresses, however, the fractions are taken regards bodies not decomposed by heat in distillation, I for a gradually decreasing number of degrees of tem- have not yet found a mixture so complex that it may perature, until finally it becomes necessary, for the attain- not be resolved by this process into its proximate conment of absolute constancy of boiling point, to take off stituents so completely that these shall have almost aba fraction for every degree, Centigrade; and to continue solutely constant boiling points. In repeated instances, thus to operate on these fractions, each representing one even from petroleums, I have obtained these constituents degree of temperature, until the desired end is attained. so pure that the contents of an ordinary tubulated retort The operator will observe that, in each series of frac-off without any essential change of temperature-i.e., charged with one of them has been completely distilled tions, in which each fraction has been taken for the same not to the amount of ° C., the thermometer frequently range of temperature, the difference between the boiling remaining absolutely constant for more than half an points of any two contiguous fractions is nearly the same as the difference between any other two contiguous frac- of distilled water. This state of purity, I think I hour-a constancy of boiling point not exceeded by that tions-in other words, that the difference referred to safely assert, has never before been attained from such may approximates to a common difference throughout the mixtures by any system of fractional distillation. same series. Once ascertained, this difference serves as a valuable guide in determining with sufficient accuracy when to add the next fraction to the retort. By observing this systematic course, irregularities from the improper mixture of products may be avoided, and time

thus economised.

detailed results of the investigations above referred to, As I shall soon be prepared to present to the Academy may omit further allusion to them on this occasion.

I

I would remark, in conclusion, that it seems to me not improbable that this process may ultimately prove to be of great value in the arts. It is not too much to anticipate After a few series of fractionings-sometimes after that, whenever the various constituents of the mixtures two or three, variable in number, according to the nature referred to shall have been separately and thoroughly or complication of the mixture-it will be found that studied in a pure state, some of them may be found to some of the fractions are considerably larger than others possess properties which will give to them great comfor the same range of temperature, indicating approxi-mercial value, sufficient to justify the expenditure necesmately the ing points of the several constituents. sary to separate them in large quantities. But fractions of constant boiling point, or those the boiling points of which cannot be sensibly changed by further fractional condensation, are not obtained, as already mentioned, till after repeated careful fractioning for every degree of temperature. When fractioning for every degree, it is important to use every precaution to protect the thermometer from external influences, and to carefully apply the corrections for variations in the atmospheric pressure. This may even be desirable earlier; but it is of so much importance in the case specified, that, if omitted, the operator would be liable one day to mix products which he had separated the day previous.

In this way certain larger fractions are obtained, which are not susceptible of further alteration in their boiling points; but there are yet considerable quantities of liquid in the intermediate fractions, which still continue to change more or less in each succeeding operation. When the fractions of constant boiling point have once been obtained, if it were not important to test for other bodies in the intermediate fractions, the operation might here

PHARMACY, TOXICOLOGY, &c.

Cause of the Solidification of Balsam of Copaiba by Lime
and Magnesia, by M. ROUSSIN.*
THE cause of the solidification of balsam of copaiba has
been until now either unknown or unappreciated. We
know, for example, that genuine balsams of the best
quality often resist solidification, whilst products of a
very doubtful quality rapidly solidify. The following
experiments, selected from a larger series, seem to throw
some light upon the question.

with a twelfth part of its weight of quicklime reduced
If balsam of copaiba of the very finest quality is mixed
to a very fine powder (it is necessary to employ rich
lime) no sign of solidification takes place, and the sub-
stances might remain in contact for any length of time
without undergoing any combination. If, into such a

Journal de Pharmacie et de Chimie, April, 1865.

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