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fluid with 125 times its volume of oxygen, but I added acid enough to dissolve 30 grammes (463 grains) of the deut-oxide, being careful also to preserve the acidity such, that at the end of the operation I could dissolve about 20 grammes (309 grains) of the deut-oxide, without the aid of sulphuric acid; but I have ascertained that, when the fluid contains nearly 50 volumes of oxygen, it allows so much gas to escape from one day to the next, that there is no advantage in continuing to oxygenate it by the deut-oxide.

5. When the fluid is oxyginated up to the required point, it is to be saturated with deut-oxide, retaining it at the same time in ice. Abundant flocculi of silex and alumine soon separate from it, which are generally coloured yellowish-brown, by a little of the oxides of iron and manganese. The whole should then be thrown quickly on a cloth, enclosed in it, and strongly compressed. This operation cannot be done well except by two persons, and should be performed rapidly; for though there is but a very minute quantity of oxide of manganese, it is sufficient to produce a considerable disengagement of oxygen.

6. As the fluid which has passed the cloth may still retain a small quantity of silex, iron, and manganese: and as it is necessary to separate all these substances, it is again to be surrounded by ice, and barytes water added to it, drop by drop, the whole being stirred. If, when the barytes is in such excess as to be slightly sensible to coloured paper, there is no precipitate, it that all the oxide of iron and manganese are separated; if proves they have not been completely separated in the preceding operation, they will by this.

Immediately on the separation of them, the fluid must be placed in two or three filters; for the oxide of manganese disengages so much gas, that it cannot be removed too quickly. Sometimes double filters are required, because the gas separating the paper, tears those that are single. Sometimes also, to avoid losses, the small quantities which remain in the filters first used, must be placed on fresh filters. Afterwards all the filters should be compressed in a cloth, to separate the water from them. Those which contain a comparatively consi

derable portion of manganese, become so hot as to burn the hand.

7. The fluid which now contains only hydro-chloric acid, water, and oxygen, is placed in the glass it was first prepared in, and its temperature lowered by ice, as before. Then, stirring it continually, sulphate of silver, prepared by dissolving oxide of silver in sulphuric acid, is to be added, by small quantities at a time; and it is essential that the sulphate contains no free oxide. The sulphate is decomposed by the hydro-chloric acid, and there results water, chloride of silver which precipitates, and sulphuric acid in place of the hydro-chloric. When the quantity of sulphate of silver added is sufficient to decompose perfectly all the hydro-chloric acid, the fluid suddenly becomes clear; until that is the case, it remains turbid. As it is required that no hydro-· chloric acid should remain, so also no excess of sulphate of silver should be present; and, therefore, the fluid must be tested successively by nitrate of silver and muriatic acid, very small quantities of the fluid being used for this purpose,

When the proportions are well adjusted, the fluid is to be passed through a filter, and the filter, after being allowed to drain, is to be compressed in a cloth. The fluid obtained by the compression, must be again passed through a filter, in consequence of a slight degree of turbidness.

8. The object of the preceding operations has been to obtain a fluid composed of water, oxygen, and sulphuric acid. But this acid must be separated; for this purpose the fluid is put into a glass mortar, surrounded by ice, and slaked barytes, very pure and finely powdered, is to be added by small portions at a time; it is to be rubbed again in the glass mortar, and when it is all united to the acid a fresh portion is to be added. When the fluid scarcely reddens litmus paper it is to be filtered, and the filter compressed in a cloth; then after having united the two fluids they are to be stirred, and the saturation of the acid completed by barytes water. There must even be a slight excess of barytes water added to separate all traces of iron; and, above all, of manganese, which the fluid may still contain; and it is of importance to remember, that it must be filtered imme

diately after, with all the precautions before given. The excess of barytes may then be precipitated by a few drops of weak sulphuric acid, and it is better to leave a slight excess of the acid present, rather than of the base, because the last tends to disengage oxygen, whilst the first renders the combination more permanent.

9. Finally, the fluid, which may be considered as pure oxygenated water, diluted with common water, is to be put into a clean glass having a foot, and this glass placed in a large capsule, two-thirds full of concentrated sulphuric acid. This apparatus is to be placed in the receiver of an air-pump, and a vacuum made. Pure water having a greater tension when in vapour, than oxygenated water, evaporates more rapidly, so that at the end of two days the fluid will contain perhaps two hundred and fifty times its volume of oxygen. The following observations must be attended to:

The acid must be agitated from time to time.

It happens sometimes that, towards the end of the evaporation, the fluid disengages a little gas, which is indicated by the variation of the mercury in the gauge. This disengagement is occasioned, no doubt, by extraneous substances which remain in the fluid; it may be stopped by the addition of two or three drops of extremely dilute sulphuric acid.

Sometimes the fluid will deposit some white flocculi of silex. This should be separated. The fluid may be decanted by a pipe with a very fine termination, and but a small quantity of it will be lost.

Until the fluid becomes very concentrated the evaporation goes on very quietly, but when the oxygenated water scarcely contains any more water, bubbles frequently rise, which burst with difficulty. At first sight, it seems as if much oxygen gas escaped, but on examining the gauge, it will appear very trifling. It will scarcely become sensible in twenty-four hours, and the alteration then observed is in part occasioned by the disengagement of gas from the sulphuric acid, belonging to a portion of the oxygenated water which has been evaporated.

The fluid may be known to be in the most concentrated state possible, when it gives four hundred and seventy-five times its

volume of oxygen at the pressure of 0m 76 (30 inches nearly,) and temperature of 14° (57.2 Fahr.) This proof is readily made by taking a small tube, on which a line is marked, and filling it with the fluid up to the line, and then diluting this quantity, which, in my experiments, was always of a centilitre, (0,030514 of c:i:) with twelve times its volume of water, and decomposing a certain quantity of this last fluid by oxide of manganese. This last experiment consists in filling a tube 15 or 16 inches long, and 7 or 8 lines wide, with mercury to within an inch of the top; then introducing the portion of diluted fluid, of which the analysis is to be made, using for this purpose a small tube of known capacity, afterwards filling the tube with the water used to wash the small measure, or partly with mercury, and then, by closing the tube with a valve, covered with tallow, inverting it, and passing in a little oxide of manganese diffused in water. The oxygen will be immediately disengaged, and nothing further is required than to close the tube with the hand, and shake it in different directions, that the contact of the oxide of manganese and the water may be ensured, and to measure the gas.

Annales de Chim. xi. p. 208,

ART. X. Description of Messrs. TAYLORS AND MARTINEAU'S Patent Apparatus, for the production of Gas from Oil, &c.

THE annexed engraving (Plate I.) represents a complete double apparatus, such as has lately been erected at Apothecaries' Hall, London; and includes all the improvements which have been suggested by the experience of the inventors, from the extended use of them in various places.

A general idea of the process may be formed from the following account of it :

A quantity of oil is placed in an air-tight vessel, in such a manner, that it may flow into retorts which are kept at a moderate red heat and in such proportions as may regulate the produc

Taylors and Martineau's Gas Apparatus.

121

tion of gas to a convenient rate; and it is provided, that this rate may be easily governed at the will of the operator.

The oil, in its passage through the retorts, is principally decomposed, and converted into gas proper for illumination, having the great advantages of being pure and free from sulphurous contamination, and of supporting a very brilliant flame, with the expenditure of very small quantities. It will, however, generally be found that some oil passes off in the state of vapour, without being decomposed; and in order to condense this, and return it again into the oil vessel, the gas is made to pass through a vessel immersed in water, by which, and its exit by a worm, the vapour is condensed again into oil, and flows at once into the oil cistern, so as to come again into use in the retorts.

As a further precaution to purify the gas from oil, which may be suspended in it in the state of vapour, it is conveyed into a wash vessel, where by bubbling through water, it is further cooled and rendered fit for use; and passes by a proper pipe into a gazometer, from which it is suffered to branch off in pipes in the usual manner.

The apparatus, of which the annexed engraving is a representation, is fit for a large establishment, and would be capable of producing from 1,600 to 1,800 cube feet of gas at one operation; or without cleaning out the retorts, which becomes necessary from time to time from the accumulation of a certain quantity of carbonaceous matter. This, and the necessary attention to keep up a moderate fire, is the only trouble which attends the use of the apparatus, and the time required for the production of the above quantity, would in general be about six hours.

The number of lights which would be supplied by 1,800 cube feet of oil gas, reckoning that they were argand burners, and employed for four hours, would be about 300, and giving a light equal to from 3,000 to 3,600 mould candles.

In order to adapt them to different establishments requiring smaller quantities of light, and to fit them for private houses, or the residences of noblemen and gentlemen, Messrs. Taylor and Martineau have made them of various sizes, accommodated to different degrees of power, and suitable by the small space they

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