needed no further preparation. We need not follow the detail of the experiments with chlorine, &c., as the effects were similar to those given above. G. C. S.

Photography upon Glass.-The author has produced photographs (Calotype) upon glass plates covered with starch, &c., by a process, which, with some modification, has probably been tried by every one who has experimented upon this interesting subject. The use of albumine (white of egg) afforded far better proofs. This substance, or rather the most liquid portion, in which is dissolved the iodid of potassium, is spread over the plate and dried at a moderate temperature.

The usual application of the aceto-nitrate of silver renders the albu men insoluble, and not liable, therefore, to be disturbed throughout the process. The proofs upon paper are far finer if one or two coats of starch paste or white of egg have been previously applied.

[A French paper of very fine surface is sometimes found which contains a large quantity of starch. A solution of iodine in iodid of potassium gives a blue color immediately on its application to this paper, which is again rendered white (or rather yellowish) on the contact of the silver solution. Hence the silver may be applied by the light of the faintest taper with great certainty, no spot being left untouchedwe can even measure very nicely the amount of silver solution by the manner in which the blue iodid is decolored. Such paper we have found to give the clearest proofs and most free from spots.]

G. C. S.

15. Note to a paper on the Chemical Nature of Gelatine, published in the American Journal of Jan., 1848, p. 74; by T. S. HUNT, (extract from a letter to one of the editors.)-In the January number of this Journal, I published a communication, the object of which was to prove that gelatine is to be regarded as the amidized species of a body identical, in composition, with dextrine. This was supported by a comparison of its analysis with a calculated formula and its metamorphosis by the action of dilute sulphuric acid which converts it into sulphate of ammonia and glucose or grape sugar. At the same time it was suggested that when taken into the stomach, its assimilation was effected by combining with it the elements of water, thus forming ammonia and dextrine of glucose. A medical friend has recently communicated to me a curious case, which seems directly to confirm this suggestion and deserves to be recorded.

A person who had for a long time been the subject of diabetes mellitus, consulted him a few months since in regard to his case. He is a young gentleman of scientific and observant habits, and has made his disease a subject of special study, marking carefully all its various phases and the changes produced in the urine by differences in diet. While confined to an exclusively animal diet, he was recommended by his physician, as an agreeable variety, to eat calves-foot jelly. This he found, to his surprise, at once increased the specific gravity of his urine, and the secretion of sugar became abundant. The patient was at this time using no sugar or farinaceous food whatever, and he observed that the formation of sugar was invariably consequent on the use of the calves-foot jelly and ceased when this was discontinued.

In this disease it is well known that the digestive function is impaired in such a manner that all farinaceous substances ingested are convert

ed into glucose, (a change which there is reason to believe, takes place also in the normal digestion of these substances,) after which no farther assimilation goes on, but the sugar formed is created by the urinary passage. In the present case it is evident that the gelatine had been decomposed in the manner suggested and that the sugar incapable of assimilation had passed off in the urine. In no other manner can we account for this otherwise singular fact; but upon the present view of the constitution of gelatine, it is just what we should expect. It is indeed a direct proof, and furnished as it is, by a cautious and intelligent observer, who had no theory to sustain, is of peculiar value.

A comparison of the quantity of ammonia in the urine when the pa tient was subsisting upon a flesh diet, and one of gelatine, would be of much interest and would, doubtless, show in the latter case, a greatly increased excretion of ammoniacal salts.

Montreal, April 22, 1848.

16. Purifying Liquids by Galvanism, (Patent Office Rep. issued in 1848, p. 41.)—A patent has been granted for an interesting process, by which a feeble galvanic power is employed to separate salts, acids or alkalies from water or other liquids. Two porous vessels containing water are partly immersed in the liquid to be purified, and a zinc plate placed in one vessel and an iron plate in the other vessel. Other metals would answer, but the inventor prefers the above. The zinc and copper plate being connected by a wire, galvanic action is established, and the salts or other soluble matters are carried through into the porous cups, and these accumulate in one or the other according to the electrical relations of the impurities.

17. Decomposition of Substances by Steam, and Manufacture of Sulphate and Muriate of Potash, (Patent Office Report for 1847, Washington, 1848, p. 27.)-The most interesting and probably the most valuable of the patents granted during the last year, under the subject of chemistry, are two which have been granted to an American citizen, now residing in England. One is for the manufacture of sulphate and muriate of potash from feldspar, and the other for decomposing alkaline salts by the action of steam at a high temperature. The latter appears highly interesting as a purely scientific discovery, apart from its practical value. In this exhibition of the solvent power of steam, we see at once a new, powerful and most economical chemical reagent.

In the process of decomposing feldspar, the inventor heats together a potash feldspar, lime or its carbonate, and the sulphate of either lime, baryta or strontia, and afterwards lixiviates the mixture with water. The heat is to be kept at or above redness. In obtaining the muriate of potash, the muriate of either soda, lime or iron is added to the potash feldspar, in place of the sulphate above mentioned, the modus operandi being substantially the same as in obtaining the sulphate.

The process of decomposing salts by steam is so replete with interest and novelty, as to warrant the citation in full of its description by the inventor.

My invention consists in a method of decomposing the sulphates and muriates of the alkalies and alkaline earths, by exposing them at a high temperature to a current of steam or vapor of water, by which the acid is carried off, and the alkaline base either remains free, or enters into combination with some third substance provided for that purpose.

To decompose sulphate of lime, and obtain from it sulphuric and sulphurous acids, and free lime, I proceed in the following manner: I have a fire-clay cylinder of close texture, and of any convenient size, placed vertically in a furnace, and provided with openings at the top and bottom, for charging and discharging, which openings are capable of being closed air-tight. To the top of this cylinder I adapt an escape tube of fire-clay, for conveying off the acid vapors; and to the bottom, for the admission of the steam, I adapt another clay pipe, connected with a steam-boiler, by a series of fire-clay tubes, which are to be kept at a red heat. In order to diminish the corrosion of the cylinder by the sulphate of lime or the lime itself, I line it with a coating of native carbonate of magnesia, applied in a manner similar to the usual clay linings of chemical furnaces. I fill the cylinder with pieces of sulphate of lime, about a quarter of an inch in diameter, and having luted the openings air-tight, I heat the cylinder and its contents to a high red heat. I then pass steam from the boiler, through the red hot clay tubes, into the bottom of the cylinder, and up through the charge. The heated steam, in its passage through the pieces of sulphate of lime, carries off the acid in the state of sulphurous acid and oxygen, with sometimes a little sulphuric acid mixed with it. The acid vapors pass off by the escape tube at the top of the cylinder, and I convey them by stone-ware tubes into a leaden chamber, in order to combine them into sulphuric acid by the usual means. I take care that the heat is not raised so high at first as to melt the sulphate of lime in the cylinder, but I increase it towards the end of the operation, the charge becoming more infusible when partly decomposed. I have an opening in the tube conveying off the acid vapors from the top of the cylinder, by means of which I examine the vapors from time to time, and from the relative acidity of these, ascertained by the usual tests, I judge of the progress of the operation. I regulate by a stop-cock the quantity of steam passed through the charge in the cylinder, maintaining the supply at that point which produces the greatest quantity of acid in the vapors. When the vapors cease to contain any notable proportion of acid, the cylinder and its contents being at a high red or low white heat, I shut off the steam, withdraw the charge from the cylinder by the lower opening, and put in a fresh one to be treated like the first. The charge thus operated upon will be found to consist chiefly of caustic lime. When I wish to obtain the acid and alkaline base from the sulphate of magnesia, I first drive off by heat all its water. I then introduce it, in small pieces, into a cylinder such as I have before described, and operate upon it in the manner directed for the sulphate of lime. But I take care to keep the heat at low redness at first, to prevent the fusion of the charge, which would choke up the cylinder and prevent the passage of the steam. The decomposition of the sulphate of magnesia takes place at a much lower temperature than that of sulphate of lime, (a low red heat is sufficient,) and a considerable part of the acid is given off in the state of sulphuric acid. When the charge has been treated as directed, the residue will be found to consist chiefly of caustic magnesia.

When I wish to decompose the sulphates of baryta and strontia, I operate upon them in a reverberating furnace. This mode is less adSECOND SERIES, Vol. VI, No. 17, Sept., 1848.

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vantageous for the manufacture of sulphuric acid than the use of the close cylinder formerly described, but I prefer it for the two last mentioned salts, because I consider their bases the more important product of their decomposition, and the hydrates of these alkalies, and particularly that of baryta, being fusible, would have much tendency to corrode the interior of the cylinder, at the heat necessary to decompose the salts. I use a common reverberatory furnace, with its hearth cov ered with a compact bed of native carbonate of magnesia, three or four inches thick. Several clay steam pipes are introduced through the roof of the furnace, so as to throw a current of heated steam over the whole width of the hearth; these pipes are connected with a steam-boiler by a series of fire-clay tubes kept red hot. The sulphate, broken into pieces of about half an inch in diameter, is spread over the lining of carbonate of magnesia on the hearth of the furnace, and brought to a high red or low white heat. A current of steam is then admitted from the boiler, through the red hot tubes, upon the charge.

The acid of the sulphate is carried off by the steam, and when I wish to condense it, the acid vapors are conveyed along with the gases of the fire, into a leaden chamber, to be combined into sulphuric acid by the usual means. The quantity of steam thrown upon the charge is kept at the point which produces the most rapid evolution of acid, and the charge is stirred occasionally, so as to expose fresh surfaces to the action of the steam. As the contact of deoxydizing gases with the sulphate is injurious, I admit, if necessary, by suitable openings above the fuel, such an excess of air as will render the atmosphere in the furnace oxydizing. The sulphate of strontia requires a higher heat than the sulphate of lime for its decomposition, and the sulphate of baryta still higher than the sulphate of strontia.

When the sulphate of baryta is partly decomposed, the mass melts and becomes more fusible as the decomposition proceeds. I judge of the progress of the operation by testing a portion of the charge from time to time; when it dissolves altogether or nearly so in dilute nitric acid, I withdraw the charge which now consists chiefly of the hydrate of baryta or strontia. To obtain muriatic acid, and the hydrates of baryta or strontia, or caustic lime from the muriates of these bases, I employ the same process as that above described for the decomposition of the sulphate of baryta.

The sulphates of potash and soda may to some extent be decomposed by being subjected at a high temperature to the action of a current of steam, in the manner directed for the decomposition of the sulphate of baryta. But owing probably to the volatile nature of the bases of these salts at a high temperature, no large proportion of them can thus be obtained in a free state. To aid therefore the decomposing action of the steam, I employ some substance capable when mixed with these sulphates, highly heated and exposed to steam, of forming a combination with their alkaline bases which shall yet when cold give up the alkali to the action either of water or of water and carbonic acid.

Of the large class of substances possessing these properties, which for convenience I will call combining substances, I prefer to use either alumina or the subphosphate of alumina. The alumina is prepared by strongly igniting the sulphate of alumina, or by any other well known

process. The subphosphate of alumina is prepared (as directed in chemical works) by mixing solutions of the phosphate of soda, and the sulphate of alumina, and adding to the solution a slight excess of ammonia. I mix the alumina in the state of powder with an equal weight of the sulphate of potash or of soda also powdered, and spread the mixture upon the hearth of a reverberatory furnace, such as I have before described for the decomposition of the sulphate of baryta. The mixture is then heated, exposed to steam, stirred, and the operation conducted in all respects in the manner described for the treatment of the sulphate of baryta. When it is desired to collect the sulphuric and sulphurous acids produced by the decomposition of the sulphates of potash and soda, I prefer to moisten the mixture of alumina and the sulphate with water, and form it into balls about half an inch in diameter, which I heat and expose to steam in a close cylinder in the manner formerly described for the sulphate of lime. When a specimen of the charge shows by the usual tests that it contains no notable proportion of sulphate undecomposed, the operation is completed. I then withdraw the charge, lixiviate it with hot water, and when the clear solution of aluminate of potash or soda thus obtained has become cold, I pass through it an excess of carbonic acid until no more precipitate of alu mina is formed. The clear solution of carbonate of potash or soda is then drawn off and evaporated. The alumina thus recovered is again used as the combining substance. When I wish to obtain the aluminate of potash or of soda, I merely evaporate the solution above described without introducing the carbonic acid.

The muriate of potash or of soda I merely evaporate the solution above described, without introducing the carbonic acid.

The muriate of potash or of soda may also be decomposed when in a fused state by the action of steam; alumina or the subphosphate of alumina being present, the operation is to be conducted in all respects in the same manner as that just described for the sulphates of potash and soda. But owing to the great volatility of the muriates of potash and soda when exposed at a high temperature to a current of air or steam, a large quantity of the muriate will escape with the steam and gases of the fire in the state of vapor undecomposed, and will be lost or will be difficult to condense. I prefer therefore to effect the decomposition of the muriates of potash and soda by causing their vapors, intimately mixed with highly heated steam, to pass slowly through a mass of small pieces of alumina kept at a high red heat. I use for this purpose a vertical fire-clay cylinder lined with a coating of native carbonate of magnesia to diminish the corrosion of its sides by the alkali, and made with convenient openings at top and bottom for charging and discharging, which openings should be capable of being closed air-tight. I arrange a cast iron retort so that its tube enters directly the cylinder near its bottom. The retort should have a charging door at the top capable of being made air-tight, through which is introduced the muriate of potash or soda to be decomposed.

The muriates of potash and soda will not vaporize freely when fused and highly heated, unless the atmosphere above them is continually changed. This may be effected by a current of steam, and I find that I can sufficiently regulate the quantity of the salt volatilized from the