Obrazy na stronie
PDF
ePub

as a grey powder, and then has the composition N Fe, and is consequently an ammonium in which all the hydrogen is replaced by iron. The formation of the nitride is explained in the following way:-Ammonia is first decomposed, the hydrogen uniting with the chlorine of the ferrous chloride to form hydrochloric acid, which on its part combines with some ammonia to form salammoniac. The iron at the same time combines with the nascent nitrogen and forms the nitride, while the excess of hydrogen is set free. This mode of formation is the more probable, but it may also be supposed that the nitrogen and iron combine directly at the moment they are free, according to the following equation:NFe +4HCl + N.

4FeCl +2NH3

[ocr errors]

The author next enters upon the formation of the nitride by the action of ammonia on metallic iron, showing the influence of time and temperature on its production, and then goes on to describe the decompositions, among which we find the following:-The iron obtained by heating the nitride in hydrogen has a silver-white colour, is extraordinarily ductile, and so soft that it may be cut with ease by an ordinary knife. It dissolves in acids without leaving any residue, and is certainly the purest form of iron yet prepared. Its specific gravity is 6'03. It oxidises in the air as easily as ordinary iron, and more quickly in moist air at 100 or 120° C. It possesses also the property of condensing water on the surface when in contact with atmospheric air; nitride of iron has the same property. We may return on another occasion to the author's remarks on Fremy's theory of the formation of steel, which occupies the remainder of the paper.

The next chemical paper is by Dr. A. Steinbeck, "On Stasfurtite," in which the author confirms the accuracy of the formula of Heintz and Gievert,

z(3MgO+4BoO,)+MgCl+HO.

A paper "On the Estimation of Carbonic Acid in Coal Gas," by Rudorff, follows. The author's method is only adapted for strict analytical purposes, and is too complicated for ordinary examinations. A drawing of the apparatus accompanies the account of the method.

The next paper is by Rudolph Weber," On several Compounds of Pentachloride of Antimony," in which he describes compounds of this body with chloride of phosphorus, oxychloride of phosphorus, chloride of selenium, chloride of sulphur, and with water.

The remaining chemical papers have no particular interest, but we may mention one by G. Tschermak, “ On the Chemical Composition of Felspar," which may be worth the attention of those interested in mineralogy.

Among several papers of physics of great value, we may mention one" On a New Improvement in the Mercurial Airpump," by J. C. Poggendorff, which is illustrated by a drawing.

Chemisches Central Blatt. Nos. 25 and 26.

The only novelties we find in these two numbers are a few short notices of things of practical interest, and these we transfer to our "Miscellaneous."

NOTICES OF PATENTS.

GRANTS OF PROVISIONAL PROTECTION FOR SIX MONTHS.

Communicated by Mr. VAUGHAN, PATENT AGENT, 54, Chancery Lane, W.C.

1349. H. A. Bonneville, Rue du Mont Thabor, Paris, "Improvements in hydrometers for ascertaining the strength of spirits and the specific gravity of fluids."A communication from C. A. Valson, Rue de Pouthieu, Paris. -Petition recorded May 15, 1865.

1579. J. M. Dentith, Connah's Quay, Flintshire, North Wales, "Certain improvements in the manufacture and

[blocks in formation]

532. T. Routledge, Sunderland, and T. Richardson, Newcastle-upon-Tyne, "Improvements in the treatment and utilisation of certain products obtained in the manufacture of paper or of paper stock."--Feb. 25, 1865.

599. R. A. Brooman, Fleet Street, "Improvements in refining sugar, and in apparatus employed therein." A communication from A. Guillon, Nantes, France."3, 1865.

March

788. R. A. Brooman, Fleet Street, "Improvements in the preparation of hydrated oxide of chromium." A communication from C. Kestner, Thann, France.-March 21, 1865.

1393. J. A. Coffey, Gracechurch Street, "Improvements in distilling apparatus."-May 20, 1865. 534. F. Claudet, Coleman-street, London, "Improvements in the preparation of certain iron ores or residues for use in the blast furnace."-Petition recorded February 25, 1865.

572. G. H. Barth, Highfield Villas, St. Pancras, "Improvements in condensation and refrigeration of vapours and fluids."-March 1, 1865.

590. W. E. Newton, Chancery Lane, "An improved process and apparatus for impregnating wood with chemical solutions."-A communication from E. Bazin and J. Hémery, Rue St. Sebastien, Paris.-March 2, 1865.

611. R. A. Brooman, Fleet Street, "Improvement in machinery for obtaining motive power from ammoniacal gas.' A communication from J. Flandrin, Paris.March 1865. 4:

[ocr errors]

629. T. Nicholson, Gateshead, county of Durham, An improved process of, and apparatus for, making caustic liquor or caustic lees."-March 6, 1865.

668. G. F. Ansell, Russell Square, "An improved mode of, and apparatus for, ascertaining and indicating the presence of explosive gases."-March 9, 1865.

64

703. J. Webb, Lawrence Pountney Lane, London, Improvements in the application and utilisation of certain materials suitable for the manufacture of paper.' A communication from J. J. Mouteiro, Lisbon,-March 13, 1865.

727. W. E. Newton, Chancery Lane, "Improvements in apparatus for distilling oils and other liquids from coal and other substances." A communication from W. G. W. Jaeger, Baltimore, Ma., U.S.A.-March 15, 1865.

CORRESPONDENCE.

Detection of Aconite.

To the Editor of the CHEMICAL NEWS. SIR,-I see by the newspaper reports of the Pritchard case that Dr. Penny has detected aconite by chemical means. Can you or any of your readers tell me of reliable tests for this poison? I have hitherto laboured under the impression that aconite could not be detected chemically, and should be glad to know the method by which it was identified. I am, &c.

ENQUIRER.

London, July 8. [We believe our correspondent is mistaken. Dr. Penny relied on comparative physiological tests.-ED. C. N.]

Royal Institution of Great Britain.-General Monthly Meeting, Monday, July 3, 1865.-The manager, reported, that in pursuance of the deed of endowment, they had appointed Thomas Henry Huxley, Esq., F.R.S. to be Fullerian Professor of Physiology.

MISCELLANEOUS.

Death of Dr. Daniell.-We regret to have to announce the premature decease of this gentleman, whose valuable contributions to our knowledge of the economic botany of Western and Central Africa and China are well known to many of our readers. His latest paper, on the kola nut, a new source of theine, has but recently appeared in our pages, and further communications on the same subject were promised. But incessant labour in some of the most unhealthy parts of the world had effectually broken up a strong constitution, and the Doctor died on June 26 at the comparatively early age of 47.

The Mysterious Death at Dawlish.— Dr. W. B. Herapath has forwarded to us a copy of the Dawlish Times containing an answer to the letter of Mr. W. Herapath, sen., which appeared in our number for June 9. We have no space for the letter, but we may say that Dr. Herapath believes it impossible that Mrs. Williams could have swallowed arsenic and strychnia at the same time. His theory is that the deceased first took the arsenic, and finding no effects in three or four hours became impatient, and then took the strychnia. But as the Doctor found no strychnia in the stomach he supposes that she spat the greater part of it out, and yet sufficient remained in the mouth to cause death in the course of half an hour or so. How it was that, under these circumstances, the twentythousandth part of a grain of strychnia which Dr. Herapath says he should have detected, did not find its way to the stomach we are unable to tell. We cannot say that this letter does much to clear up this "mysterious" case, which, however, does not appear to us so very mysterious. The Search for the Philosopher's Stone in 1865. -Let those who believe that the hope of transmuting the baser metals into gold expired with the last century, shrinking from the glare of light which in this boasted age dispels all idle dreams, read the following advertisement, which appeared in the Times of April 4, 1865:

"To STUDENTS IN ALCHYMY.-Any gentleman who may require an Assistant can be recommended to an industrious foreigner, who has studied the books of the alchemists for the last fifteen years, and is a good experimentalist. He is now in Transylvania, but every information will be given by applying to Chas. F. Zimpel, M.D., 182, Marylebone-road.'

Nor is the search now-a-days confined to laboratory experiments. Rumour asserts that an extraordinary rise in the price of bismuth which occurred last year was caused by the purchases of a joint stock company, established for the purpose of carrying out on a large scale the discoveries of a gentleman who, it was understood, had succeeded in perfecting the preparation of the "Stomach of Anthion," or the "Sharpness of the Eagle," or whatever may be the name of the needful alkahest. Had these modern patrons followed the examples of the shrewd Medici, who sent Augurellus of Rimini an empty purse, they had contented themselves with the purchase of an iron safe. They did more. Their "Subtle" did not profess to turn all metals into gold; their spits and pans and andirons were not available; no use to strip the churches of their coverings. They bought bismuth. Did their imagination, I wonder, like Sir Epicure's in the play, run riot among pictures such "as Tiberius took from Elephantis," among mistresses "with great smooth marbly limbs," among mists of perfume, and baths "from whence we will come forth and roll us dry in gossamer and roses;" did they surround themselves with poets and flatterers, "the pure and gravest of divines," dream of Apician dainties served "in Indian shells, and dishes of agate set in gold," and of raiment "such as might provoke the Persian?"

"This day
Give lords th' affront.

ingots, and to-morrow

To-morrow came and with it :

"Is all lost, Lungs? will nothing be preserved
Of all our cost?"-"Faith, very little, Sir;
A peck of coals or so !"

In this instance, however, the result was not quite so itch off "the scraped shards". lachrymose. Still-even counting the "cure for the '-a fiasco.

century for the fulfilment of the prophecy made by the There is time enough yet, however, in this nineteenth in his memoir on Azote in the Annales de Chimie, No. 100, eminent Göttingen professor, Dr. Christopher Girtanner, that this century will assuredly give birth to the transmutation of metals, when every chemist and every artist will make gold; when kitchen utensils will be made of silver, and even of gold, which will contribute more than any. thing else to prolong life, poisoned at present by the oxides of copper, lead, and iron that we daily swallow with our food. (Pettigrew.) This is a prosaic, but eminently practical way of looking at the rejuvenescent power of the wonderful Elixir, and one likely to prove more efficacious, I take it, in retarding the advances of old age than that method to which is attached the name of the unknown Hermippus-puellarum anhelitu. A. Challsteth, Notes and Queries, June 10, 1864.

Trial of Dr. Pritchard.-The following is an abstract of Dr. Maclagan's report of the results of the chemical investigation in the case of Mrs. Pritchard:"I made a trial experiment, in presence of Dr. Littlejohn and my assistant, Dr. Arthur Gamgee, with three drachms of the deceased's urine, and obtained from this unmistakeable evidence of the presence of antimony. Being obliged to go to London, I requested Dr. Gamgee, in conjunction with Dr. Littlejohn, to carry on the following preliminary process in my absence. The whole contents of the intestines were evaporated to dryness on a water bath, so as to obtain a solid residue; one-half of this residue was digested with water acidulated with tartaric acid, and filtered, by which a solution measuring two ounces and five drachms was obtained, in which any antimony present in the intestines would be found. One ounce of this fluid was subjected to a stream of sulphuretted hydrogen gas, and the orange-yellow precipitate which formed was collected on a filter and washed. This precipitate, and the remainder of the tartaric acid solution, were reserved for my examination on my return to Edinburgh on the 24th of March. I then subjected these materials to the following examination. The orange-yellow precipitate was boiled in a tube with pure hydrochloric acid, and the solution thus obtained was mixed with water, when a white precipitate formed. The fluid containing this precipitate was subjected to a stream of sulphuretted hydrogen gas, and again gave a deposit of an orangeyellow colour.

"One fluid drachm of the tartaric acid solution was treated by Reinsch's method, and another fluid drachm was treated by Marsh's process. By each of these wellknown methods, and thus operating upon a quantity of fluid corresponding to a forty-second part of the contents of the intestines, I obtained unequivocal evidence of the presence of antimony. By digesting a small quantity of the dried residue of the intestinal contents with distilled water, filtering and subjecting the filtrate to Reinsch's process, I readily ascertained that the antimony was here present in the form of a compound soluble in water. There are only two preparations of antimony occurring in commerce which are soluble in water; the one of these, the chloride, is a strongly acid, dark-brown, corrosive fluid, totally unsuited for internal administration; the other is what is known scientifically as tartarised antimony, and popularly as tartar emetic, a colourless substance, possessed of comparatively little taste, and in daily use as a medical agent. I have no doubt, and shall assume in the following statements, that the antimony found in Mrs. Pritchard's body was taken in this form.

taken at no greater interval than a period of a few days previous to death.

"7th. That the period over which the administration had extended cannot be determined by mere chemical investigation, but must be deduced from the history of the case, with which I am unacquainted. "DOUGLAS MACLAGAN."

Composition of the Gas of some Continental Cities.—

Hydrogen
Marsh gas
Carbonic oxide

Condensible hydrocarbons
Carbonic acid.
Nitrogen.

[ocr errors]

Heidelberg. Breslau.

Bonn.

41'05 40'70 39'80

[ocr errors]

40'71 39.82

43°13

7.64 4'01

4'66

7.28 4'96

4'75

0'41

3'02

4:65

0.58
2'75 10'10

The analyses were made according to Bunsen's method.-
Chem. Cent. Blatt., 25, 399.

"The remainder of the acid solution, amounting to one ounce and three drachms, was subjected to a process intended to determine the quantity of antimony present "6th. That I am inclined to believe that it had not in the contents of the intestines; but though the presence been administered, at all events in any great quantity, of this metal was determined with the greatest facility, I within a few hours of her death. Had this been the case, found that the amount yielded by the materials which II would have expected to have found at least some traces used was too small to enable me to weigh it with sufficient of it in the contents of the stomach, and more in the conaccuracy. The presence of antimony having tents of the intestines; whereas none was found in the been already ascertained in the urine, the remainder, former, and the amount found in the latter seems to be amounting to seven ounces, was employed to determine its amply accounted for by the bile impregnated with the quantity. The quantity of sulphuret was readily poison discharged into them from the liver. weighed, and found to be rather more than one-tenth of a grain (o 1078 grain). This corresponds to nearly onefourth of a grain (218 grain) of tartar emetic. A little more than half an ounce of bile was obtained from the gall-bladder. By Reinsch's process 50 minims readily gave an antimonial deposit. The remainder of the bile, amounting to four drachms, was used to determine the amount of antimony in it, and it yielded sulphuret of antimony corresponding to more than one-tenth of a grain (0*121 grain) of tartar emetic. The total quantity of blood was six and a-half ounces. One-half was subjected to Reinsch's process, and readily gave evidence of the presence of antimony. A portion of the liver, weighing less than four ounces (1460 grains) was subjected to Reinsch's process, and a sufficient amount of antimony was found to coat rather more than four square inches of copper foil. [Having described further experiments, the report goes on.] I obtained an amount of antimony in the state of sulphuret (o'1234 grains) corresponding to a quarter of a grain (0.25 gr.) of tartar emetic, the amount contained in the whole liver being almost exactly four grains (3'93 grs.). I next examined the remainder of the solid organs removed from the body of Mrs. Pritchard, and have to state that I have found more or less of antimony in the whole of them. On the 29th of March I received from the hands of John Murray, Sheriff-officer, Glasgow, two parcels of clothes, with sealed labels attached to them, with a view to my examining some stains upon them. . . I examined such of the stains on these articles as appeared of importance, confining my experiments to a search for antimony, and I have to state that, whilst with many of the stains the result was entirely negative, I found antimony on the following:-1st. On the chemise, from a stain obviously of discharge from the bowels, and which had been marked by me A. 2nd. On one of the sheets, distinguished by me as No. 1, in a stain marked by me B. 3rd. On the other sheet, distinguished by me as No. in a stain obviously of urine, marked by me A. 4th. On a toilet cover, in a stain of a reddish colour, looking like wine stain. From the experiments, the details of which are given above, I have been led to the following conclusions :

2,

To Etch in Relief on Zinc and Gild the Etching.-Boettger first makes a solution of one part of dry chloride of platinum and one part of finely powdered gum arabic in twelve parts by weight in water. With this solution he writes on clean and polished zinc with an ordinary goose quill. The writing immediately appears black from the deposition of platinum black, and now, before the writing is dry, the plate is dipped for a few moments into a solution of aurocyanide of potassium. The whole plate thus becomes covered with a very thin coating of gold; but if it be placed in dilute nitric acid (one part of acid sp. gr. 12 and sixteen parts of water) the layer of gold peels off the zinc, but remains fast adherent to the platinum writing. This part of the operation may be assisted by rubbing the acid on the plate with a soft camel's hair pencil. By continuing the action of the acid the writing may be obtained in tolerably strong relief.-Journal für Prakt. Chem., vol. 94, p. 440.

ANSWERS TO CORRESPONDENTS.

Vol. XI. of the CHEMICAL NEWS, containing a copious Index, is now ready, price 11s. od., by post, 118. 6d., handsomely bound in cloth, gold-lettered. The cases for binding may be obtained at our Office, price 18. 6d. Subscribers may have their copies bound for 2s. 6d. if sent to our Office, or, if accompanied by a cloth case, for Is. Vols. I. commenced on July 7, 1865, and will be complete in 26 numbers.

"1st. That Mrs. Pritchard had taken a large quantity and II. are out of print. All the others are kept in stock. Vol. XII, of antimony in the form of tartar emetic.

"2nd. That having regard to the absence in her case of any morbid appearances sufficient to account for death, and to the presence in it of a large quantity of a substance known to be capable of destroying life, her death must be ascribed to the action of antimony.

"3rd. That it is most unlikely that this poison was taken in a single large dose. Had this been the case, I should have expected to have found some more decided evidence of irritant action in the mouth, throat, or alimentary canal.

4th. That from the extent to which the whole organs and fluids of the body were impregnated with it, it must have been taken in repeated doses, the aggregate of which must have amounted to a large quantity.

"5th. That from the large amount found in the liver, from its ready detection in the blood, and from its being found passing so copiously out of the body by the bile and urine, it is probable that some of the poison had been

of Alsace.

A correspondent asks for information on the subject of albumen prepared from the roe or peas of cod-fish, and used in the print works levigation might, perhaps, heighten the shade. Oxamide. We have no practical knowledge of the colour. Fine

D. J. 0.-1. In the air probably some would volatilise unchanged, aud some would burn to furnish carbonic acid and hydrogen. The products formed when atmospheric air is excluded have not yet, so far as we know, been described. 2. The constituents would probably include the heavier hydrocarbons.

Lucy asks if there have been any female chomists. Miss Chenevix was, we believe, the only lady who ever exercised her abilities on the products of the test-tube and the crucible. There is no reason why ladies should not study and practise chemistry, and there are many reasons why they should choose this science to occupy their leisure moments. Surely the investigation of chemical facts would be more suitable for ladies than the study of social science, surgery, and medicine.

Received.-On Chemical Nomenclature, and Observations on some

Points in the Analysis of Potable Waters, by Professor W. A. Miller,

F.R.S., &c.

Odling; "Ophthalmic Review," July.
Books Received."A Course of Practical Chemistry," by Dr.

SCIENTIFIC AND ANALYTICAL

CHEMISTRY.

On the Estimation of Uric Acid, and on the Amount
contained in Human Urine, by ARTHUR H. HASSALL,
M.D. Lond., Senior Physician to the Royal Free
Hospital.

THE quantity of uric acid contained in healthy human
urine is estimated variously by different analytical and
medical authorities, and is stated to range in the twenty-
four hours from 432 to 14:49 grains; the mean deduced
from the principal determinations hitherto made amount-
ing, according to Parkes's table, to 8.57 grains. Between
these two extremes there is a wide difference, explained
in part by the imperfect observance of the precautions
necessary for the estimation of this acid by precipitation
with hydrochloric acid.

With a view to determine the actual amount of uric acid present in healthy urine, and guided by the various facts and particulars already detailed, I have myself instituted a great variety of experiments.

[ocr errors]

second, several of the urines, and especially those first experimented upon, were not evaporated to the full extent requisite to obtain the whole of the uric acid; third, some few of the samples were evaporated at a somewhat too high a temperature; fourthly, in some instances a delay of two or three days ensued before the determination could be proceeded with. I am therefore persuaded that the real mean, instead of being 21:00 grains, is nearer 24 grains.

It is true that the mean of these results furnishes only 18 grains, but then the mean of the urea is but 488 grains. Now, taking the mean of the latter to be 5124 grains as usually calculated, and increasing the uric acid in the same relative proportion, the mean would be raised to 18.77 grains; but the mean of the urea actually obtained by myself is 592 grains, which would furnish by calculation 218, or nearly 22 grains.

It is only by following out the process in all its details with the greatest care that uniform results can be obtained, and that the whole amount of uric acid contained in any urine is separated.

In the next place, numerous experiments were made with a view to determine the amount of uric acid in the urine in various cases of disease.

The smallest amount of uric acid obtained in any case was 8.74 grs., and the largest no less than 40'5 grs., the mean of the whole being 20.00 grs. In a case of Bright's disease, in which uric acid is stated to be usually very aug-deficient, no less than 270 grs. were obtained.

The smallest quantity of uric acid obtained in any case was 12'37 grains, and the largest 40'5 grains, the mean of the whole being 2100 grains, equal to about 3 of a grain to each pound of body weight. The urea was also determined, and in nearly every instance in which the uric acid was increased the urea was also mented; and taking the mean amounts obtained of these two substances, the relation is as I part of uric acid to

28 of urea.

The amount of uric acid, therefore, separated by me is more than two and a half times that hitherto obtained by other observers.

It might be urged in objection that the deposits obtained did not consist in all cases entirely of uric acid, but in part of urates. No doubt in some instances they contained more or less urate and earthy phosphates; but then they were invariably incinerated and the amount of ash deducted, so that this objection would be un

founded.

Again, a further objection might be urged that, owing to the extent to which the evaporation was carried, the precipitates would contain a sensible amount of hippuric acid. This substance was therefore also sought for. Many of the larger deposits were treated with alcohol, the solution evaporated to dryness on a water-bath, and the extract weighed; this was, however, in no case so considerable as to reduce materially the high results obtained. The dried alcoholic residue, after having been weighed, was digested with strong boiling nitric acid, the liquid evaporated to dryness, and the product heated in a glass tube. Had hippuric acid been present, it would have been detected by the bitter-almond-like odour of nitro-benzine which would have been evolved, only a trace of which, however, was in any case perceptible. The alcohol, of course, abstracted the colouring matter from the precipitates, in amount not inconsiderable, as will be shown hereafter; but it must be remembered that the uric acid obtained by other experimenters was also contaminated with that substance.

So far from the amounts given by me being in excess, large as they are, I would here distinctly state my belief that they really fall short of what they ought to be, and this for several reasons. First, it is scarcely possible to be certain, whatever the precautions taken, that one obtains the whole of the urine voided in every case;

* Ab-tract of a communication in the Lancet, June 17, 1865. VOL. XII. No, 294.—JULY 21, 1865.

None of the samples analysed by me contained, in any considerable amount, deposits of uric acid or urates; and I believe that urines very much richer in uric acid than any I have subjected to analysis are constantly to be met with in disease, and which would furnish on the day's excretion some 50 grs. or even 60 grs. of uric acid. I obtained, in a case of ascites, from 5000 grs. of the In proof of the foregoing observation, I may state that urine no less than 10.84 grs. of uric acid, or nearly one grain to the ounce.

Of course, during evaporation the colour of the urine becomes deeper from concentration, and the uric acid precipitated will therefore take up a larger proportion of colouring matter than it would do in a very pale and dilute urine. The uric acid obtained from concentrated urine is also amorphous, in place of crystalline, as it is when thrown down from dilute urine, and it is therefore in the condition best suited for becoming stained; it is, moreover, mixed with more or less urate. The colour of the uric acid deposits obtained from evaporated urine differs greatly, it varying from pale fawn to pink and red, according to the character of the urine from which they were obtained. The amount of acid used also affects most materially the colour; thus some of the urines, to which different quantities of the acid were added, yielded deposits differing greatly in colour. In those cases in which the largest quantity of acid was used a pink precipitate formed, as though uroërythine were present, although the experiments on the same urine with the smaller amounts of acid yielded deposits of a fawn colour. This result I have observed over and over again, and it is sufficiently curious to deserve to be

[blocks in formation]

by means of hydrochloric acid are due not so much to any fault in the process itself, as to a want of strict attention to all the precautions necessary to ensure successful results.

I have found that the conditions under which the determination should be made are as follow:

1st. The quantity of urine operated upon should be large; if possible, not less than 5000 grains should be

taken.

2nd. The urine should be perfectly fresh, especially if it contain albumen, sugar, or other fermentable matter.

3rd. The evaporation should be slowly conducted for the two first thirds of the amount over the naked flame, but for the last third over the water-bath the rapidity of evaporation being carefully moderated towards the close of the process.

4th. In the case of concentrated urines-that is, of urines having a specific gravity of 1016 and upwardsthe evaporation should be carried to the extent of about one-fourteenth the bulk operated upon; but in the case of urines below that gravity the evaporation should be carried to even one-eighteenth or one-twentieth.

5th. The acid should be added only after the urine has been evaporated, and when it has become cold, 50 grains' measure of hydrochloric acid, of specific gravity 111, being added to the evaporated residue of every 5000 grains of urine taken.

6th. That since the results are so materially affected by temperature, and if the determinations are made in the spring, summer, or autumn, the evaporated urine to which the requisite quantity of acid has been added should be placed in an ice-chest, furnished daily with a few fresh lumps of ice, or in a freezing mixture, and left for forty-eight hours.

7th. That the evaporated urine containing the deposit of uric acid should be filtered through pure but not too fine paper, and one yielding but an infinitesimal amount of ash. Swedish paper is usually too fine for the purpose.

8th. That the precipitate, when collected on the filter, should be washed with cold distilled water, applied by means of a small wash-bottle, the same amount of water being employed in every case-viz., 400 grains-to the precipitate obtained from 5000 grains of urine. It is desirable, of course, that as little water should be employed as possible, on account of its solvent action on the uric acid. The experiments I have detailed in this paper show that the rule laid down by Messrs. Neubauer and Vogel, of allowing o15 grains of uric acid for every 400 grains of filtrate, is one which, applied to the urine, is practically destitute of foundation, although the amount stated represents the solubility of that acid in pure water. In every determination the filtrate and washings must be set aside for a few days in order to see if any further deposit forms, although this rarely occurs when the urine has been sufficiently evaporated.

9th. That the filters with the washed precipitate should be partially dried by placing them on thick bibulous paper, then transferred to the water-bath, and finally weighed, the latter operation being performed in a weighing tube.

10th. The filters containing the uric acid should be invariably incinerated, and the amount of ash deducted. 11th. As an additional precaution, and where extreme accuracy is desired, the precipitates prior to incineration should be digested with a mixture of three parts of absolute alcohol and one part of spirit of wine. The

colouring matter thus separated, after being properly dried in a water-bath, should be weighed and the amount deducted, the ash obtained by calcination of the residue insoluble in the alcohol being likewise subtracted.

12th. In determining the uric acid in cases of disease, it is essential that the urine should be previously carefully tested for albumen, and this, even though it may be in small amount, should be completely separated; otherwise it will be weighed with the uric acid, and so increase the apparent amount. In such cases the urine should always be filtered quite hot, or some of the uric acid may become precipitated. Again, when any urine contains a deposit of either uric acid or the urates, it is necessary to well warm the urine until the deposit is completely dissolved, in order that a fair average sample be obtained for precipitation.

may

It is stated in books that the occurrence of effervescence in any urine on the addition of a strong acid, as nitric acid, indicates the presence of carbonates. There never was a stronger instance of an inaccurate statement than this. When nitric acid is added to hot urine in a test many cases it is most copious and rapid, and causes the tube more or less effervescence invariably ensues, and in liquid to overflow. Now this effervescence is caused by the decomposition of the uric acid by the nitric acid, carbonic acid and nitrogen being evolved. In this fact I had hoped to have been able to found a process for the easy estimation of the uric acid, by measuring, in properly graduated tubes, the volume of the gases evolved. I made many experiments with this object, but I found that the process was not to be relied upon, and that it was subject to two fatal sources of error. Thus a portion of the colouring matter of the urine on the addition of nitric acid is also decomposed with effervescence like uric acid, the urine when heated for some time gradually losing a considerable portion of its colour; and secondly, when a mixture of urine and nitric acid is subjected to the prolonged action of heat, the urea likewise undergoes decomposition, carbonic acid being evolved. In the absence of colouring matter and urea, the uric acid may be readily determined with nitric acid, for I found that when uric acid, either free or combined, was diffused in hot water, it readily decomposed on the addition of a few drops of nitric acid.

A fact which I have also observed, and which deserves to be recorded in this place, is, that when nitric acid is added to a hot urine the mixture very quickly becomes of a dark or brown-sherry colour; this, by prolonged boiling of the mixture, gradually disappears, leaving the urine of its natural straw colour. This very striking change of colour would appear, therefore, to be due to the action of the nitric acid, not upon the true colouring matter of the urine, but upon some other substance, possibly hypozanthine.

General Conclusions.-The two general conclusions to be deduced from the experiments detailed in this communication are

Ist. That the whole of the statistics of uric acid are destroyed by these investigations. There is not a single figure or quantity given which can be regarded as by any means accurate or precise. The statements made as to the occasional absence of uric acid from human urine I believe to be without foundation.

2nd. That many of the statements made respecting the pathology of this acid require re-examination and revision.

Wimpole-street, May, 1865.

« PoprzedniaDalej »