is better not to employ the carbonizing process if the chemist can examine the substances which have been thrown up from the stomach by the poisoned person, or that part of them which remains behind in the alimentary canal: this process is only to be used when the first attempts have been without success. It must not be considered that if, by means of Marsh's apparatus, we obtain a metallic spot, that therefore arsenic is present; the apparatus is really only a means of collecting and condensing the arsenic, but not of directly proving its presence, for very similar spots are produced from various causes; as, for instance, glasses containing lead*, porcelain with a lead glaze, or even spots of oxysulphuret of zinc carried over by the stream of gas, if the zinc contains a little sulphur. Orfila found that by the action of a strong flame on organic fluids, peculiar spots were deposited on cold bodies, which he called fat-spots. Danger and Flandin found that partially carbonized organic tissues gave similar brown marks, arising from sulphite and phosphite of ammonia; this latter source of error can only be found when the oxidating process has not been continued long enough. The apparatus proposed by the Commission of the Parisian Academy consists of a bottle with a wide mouth, fitted with a cork, through which pass two tubes; one reaches to the bottom of the vessel, and the other is bent, and serves for the purpose of carrying off the generated gases. There is a bulb in the tube to condense the moisture; it is then bent, and communicates with a tube filled with asbestus; another longer tube is attached to this, a part of which is covered with gold leaf, it then passes through a copper screen-it is drawn out to a point at the end. Zinc, water, and sulphuric acid are put into the bottle, and the part of the tube covered with gold leaf is heated to redness; the gas, as it issues out at the fine end, may be inflamed and tested with cold bodies. If no arsenic appears, and the reagents are consequently pure, the suspected solution may be brought into the bottle by means of the tube. The arsenic is deposited on the other side of the heated part. The end of the tube may conduct the gas into a solution of nitrate of silver; metallic silver is precipitated, and arsenious acid remains in solution, which may be tested. If the zinc contain any sulphur, sulphuret of silver is formed. When the ring has been obtained it must be further examined,―

1. As to its volatility. The spots of arsenic exposed to the hydrogen flame volatilize directly; spots of antimony spread at first and vanish after several minutes, having first become much paler.

2. Its change into a volatile white powder, possessed of a garlick smell when heated in a tube open at both ends, and held in a slanting direction.

3. The spots must be treated with a little nitric acid, or rather, aqua regia. The solution, evaporated to dryness, gives with nitrate of silver a brick-red precipitate. The fat spots give light-yellow

* Louyet drew attention to the fact that several kinds of glass, when heated in the reducing flame of the blowpipe, or of hydrogen, acquire spots which are very similar to those of arsenic, but are easily distinguished by the treatment with nitric acid, and test with solution of silver.-Journ, de Pharm. 1840.

precipitates of phosphate of silver, and the residue of antimony remains unchanged,

17.

4. The metallic arsenic may be separated again by mixing the mass with a little black flux and heating in a glass tube.

With Marsh's apparatus weak traces of arsenic spots could be seen when only 3,000.00g of arsenic were present; with the above

described apparatus 3,000,000 could be observed. No arsenic could be found in organic substances in a normal state, but very easily after the receipt of the poison.

Marsh proposes the following test:-A glass plate, moistened with a solution of ammoniated nitrate of silver, is held horizontally at the distance of half an inch over the burning jet of gas. Arsenic produces the well-known yellow colour, antimony a white precipitate; if neither are present the silver is reduced.

Danger and Flandin have found, that in cases of poisoning by means of antimony, this metal is not to be found in the lungs, nerves, muscles or bones, but chiefly in the liver. The antimony may be separated in the same manner as arsenic; the carbonized organic substance must, however, be extracted with dilute tartaric acid.

Meissner has proposed a method for distinguishing antimoniuretted hydrogen from the analogous arsenic compound, and also of proving the presence of a small quantity of the former in an excess of the latter. If antimoniuretted hydrogen be passed through an alcoholic solution of potassa, soda, or ammonia, the colour of the liquid passes from yellow to brown, and metallic antimony is precipitated. Arseniuretted hydrogen produces no change of colour at all.

Another method of distinguishing whether the metallic ring obtained is arsenic or antimony, is to pass the vapour of iodine into the tube containing it, heat being applied. Iodide of arsenic is of a straw-yellow colour, shining, and of crystalline structure; iodide of antimony is reddish-yellow, dull, and has no crystalline appearance. Water dissolves the former but not the latter.-Journ. für Prakt. Chem. xxv. p. 243.

Pettenkofer employs the metallic ring formed in a tube for further experiments as to the presence of arsenic or antimony. The tube is fastened on to a bottle, out of which sulphuretted hydrogen is being evolved. The part of the tube where the ring is situated is heated by the flame of a spirit lamp; the black ring changes into beautiful yellow vapours, which are deposited a little further on. This is pure orpiment.

A ring which had been formed by antimony, when treated in the same manner with sulphuretted hydrogen, gives a kermes red amorphous sulphuret of antimony. This sulphuret is only formed when the ring is heated strongly with the blowpipe, while the arsenic compound only requires a spirit lamp, although it is formed better when the blowpipe is employed. Moreover, the red kermes, when heated for a length of time, becomes gray from its passing into the crystalline sulphuret.

As the sulphuret of arsenic is much more volatile than that of antimony, the orpiment is always deposited further away from the

flame, and the presence of both bodies may be well ascertained. A hydrocarbon prepared from four parts concentrated sulphuric acid and one part alcohol, deposits a ring which appears metallic, which, however, is not altered by sulphuretted hydrogen, and cannot be volatilized. The same behaviour is exhibited by the ring which is deposited when sulphite and phosphite of ammonia, with a little oil of turpentine, are put into Marsh's apparatus. If there is also arsenic present, the orpiment is volatilized, leaving the black ring behind. If a piece of phosphorus be put into the apparatus, a yellow ochrecoloured ring is deposited, which becomes white when heated in sulphuretted hydrogen, and is but little volatile.

Pettenkofer found all officinal preparations of antimony except tartar emetic and powder of algaroth, to contain arsenic.

Rings of arsenic so thin as to be scarcely perceptible to the eye become very evident when treated in this way, inasmuch as they take up 1 equivalent of sulphur.

The colour must not be judged of until the tube has cooled; for if the sulphuretted hydrogen be heated strongly and for a length of time, sulphur is deposited, which, however, when cool, has quite a different appearance to orpiment; moreover, the latter is soluble in ammonia, while sulphur is not. The ammoniacal solution may be precipitated with acetic acid, and the sulphuret again put into the Marsh's apparatus, and spots collected which may be volatilized by heat, and examined as to the odour. Buch. Repert. xxvi. p. 289.

Phosphoric acid containing arsenic is, according to Wöhler, much more frequently met with than is generally believed, and the arsenic easily escapes observation when it is present in the form of arsenic acid. Before the application of the test with sulphuretted hydrogen it is necessary to boil with sulphurous acid, which reduces the arsenic acid into arsenious acid, or else to use a small Marsh's apparatus. The use of sulphurous acid is strongly recommended by Wöhler in all cases where an oxidizing process has been employed.-Ann. der Chem, und Pharm. xxxix. p. 122.

On the Conversion of Ligneous Fibre into Starch, and on Amyloid. By Prof. J. Liebig.

Some time back Dr. Schleiden of Jena published a paper in Poggendorff's' Annalen' on the conversion of ligneous fibre by means of caustic potash or of sulphuric acid into starch, or some nearly allied substance. Liebig has recently made some experiments on the subject, the results of which show that Schleiden has been deceived by the action of iodine.

When linen or cotton is treated with a mixture of 1 water and 3 sulphuric acid, it assumes a gelatinous state; a sufficient quantity of tincture of iodine quickly added to it imparts to it an intense indigo-blue colour, and on suspending it in pure water it is carried off as a fine blue powder. This experiment is perfectly correct; not so the explanation. The blue colour is not produced, for instance, when previous to the addition of the tincture of iodine the

mixture of sulphuric acid and ligneous fibre is treated with water; in this case only iodine is thrown down. When moreover the blue mass is slightly warmed in water, it loses its colour and cannot again be produced on cooling by the fresh addition of iodine.

When the sulphuric acid is quickly filtered from the ligneous fibre and tincture of iodine added to the clear liquid, a dark blue precipitate is formed, which consequently arises from a substance which had been dissolved by the sulphuric acid; and this substance can in fact be isolated from the solution by the addition of water. It had hitherto been overlooked when acting on fibre with sulphuric acid, and will shortly be more accurately described by M. Hoffmann. The sulphuric acid, separated from the ligneous fibre by means of a funnel stopped with asbestus, is clear and colourless; and, on being treated with water, deposits in pretty considerable quantity a white body in fine flocks; and these it is which were coloured blue by iodine in the experiments of Schleiden. They are insoluble in cold and in boiling water, and when treated alone with tincture of iodine do not assume a blue colour, consequently they do not consist of starch; but they are coloured by iodine when precipitated at the same time with iodine from a solution. This is the case when the sulphuric acid solution is directly mixed with tincture of iodine, in which case the white body and finely divided iodine are thrown down together; but when, as above observed, a few drops of water have been mixed with the sulphate solution, so that the whole of the substance held in solution is precipitated, tincture of iodine no longer gives rise to any colour; if, again, it be redissolved in sulphuric acid, it may be precipitated by tincture of iodine with the blue colour. When the sulphate solution of the white body is kept for twenty-four hours, iodine no longer produces any colouring; but in this case no precipitate is occasioned by water.

It is evident to what false conclusions we are apt to be led respecting the nature of a vegetable substance when founded on nothing else than an accidental colouring, the true nature of which moreover is unknown. Such also is the case with Schleiden's amyloid.—Ann. der Chem. und Pharm. xlii. p. 306.

On Digestion.

Bouchardat and Sandras have been led by their experiments to a theory of digestion differing somewhat from that generally adopted. It is a generally received opinion that the food is brought into the stomach and there changed into a homogeneous gray substance of a sweetish, slightly acid taste, which still retains some of the properties of the food, and which has been called chyme. It is supposed that this so-produced chyme passes into the intestines, where it is absorbed by the orifices of the chyliferous vessels and converted into chyle. Bouchardat and Sandras believe that the substance which has been called chyme is a mixture of undissolved remains of the food, the solution of which is perhaps continued in the windings of the intestine, and of excretions from the glands and

mucous membranes of the intestines, which are destined afterwards to form the excrement; but they do not believe that this mixture is expressly prepared for assimilation.

As yet it has been supposed that the food is first dissolved in the stomach, then precipitated and converted into chyme, and finally redissolved, and then forms chyle.

But coloured fibrin gives a colourless chyle; that which is collected during the digestion of starch has very nearly the same constitution as that obtained during the digestion of fibrin.

Is it not, then, very probable that these kinds of food-fibrin, casein, albumen, gluten and starch-are not converted into chyle at all? But the question then comes to be, what are the functions of the vessels containing chyle, and of the chyle itself, which certainly is most abundant during digestion?

Experiments seem to have proved that the openings of the chyliferous vessels are destined to absorb the fatty kinds of food which have been changed into an emulsion by the gall. But this cannot be the sole use of so important a product as chyle. If good food is given to a fasting animal, and is eaten, a process of preparation instantly commences. The saliva collects in large quantities in the cavity of the mouth, as does also the gastric juice in the stomach.

If, however, the gastric juice is produced by the presence of such food, it contains considerable quantities of hydrochloric and lactic acids. These acids are evidently produced by the decomposition of the salts with which the animal economy is provided, viz. chloride of sodium and lactate of soda. If, however, we can prove the production of acids we must somewhere or other meet with alkalies.

Whilst the separation of the hydrochloric and lactic acids in the stomach is proceeding, other organs are preparing a chyle for the chyliferous vessels and the ductus thoracicus, the alkaline quality of which is proportional in strength to the quantity of acid produced in the stomach; and this chyle, which is not produced simply by a change and absorption of the food, but by a true secretion, becomes mixed with the blood so as exactly to neutralize the acid which is necessary for the solution of the food. In this way the blood may be continually renewed without undergoing any change whatever.Compt. Rend., Mai 1842, p. 680.

On Glucinium and its Compounds.

M. Awdejew has made a series of experiments on the salts of glucina, under the direction of H. Rose. Great care was used in the preparation and analysis of the chloride of glucinium. It was found to contain 87-54 per cent. of chlorine, whereas it has been supposed to contain only 66-70. When dissolved in water it forms hydrochlorate of glucina; on evaporating the solution a crystalline mass is obtained which has the composition GCI + 4 aq. [Awdejew supposes the oxide to contain one atom of oxygen.] The atomic weight of the oxide was determined from the analysis of the