distance, to admit of a sufficient quantity of air, and make a number of apertures in the wall, about two and a half inches square, with a view to compel the air to blow upon the heated surface. This method was employed more than thirty years ago, by William Strutt, Esq. of Derby, in his cotton-works. He afterwards made a great improvement on this plan, by inserting tubes in the apertures in the wall reaching near to the heated surface. By these means, the air is prevented from ascending before it comes in contact with the heated surface. A further improvement was made in this apparatus, by inserting similar tubes over the surface of the cockle, the shape of which was a square prism with a groined top. The cold air was made to pass through one half of the tubes; and the air so heated, became still more heated by being compelled to pass in a contrary order through the other half, into a chamber above, called the air-chamber. The stove, thus improved, has been employed by Messrs. Strutts in their works ever since, with complete success, and is similar to that by which the Derbyshire General Infirmary is warmed. This stove has been fixed in different parts of the country and in London, sometimes with success; but so many circumstances besides the stove itself interfere, in arrangements of this kind, that the plan has failed in many instances. And such will ever be the case with the best inventions, in the hands of men who are unacquainted with the principles on which they are founded.

Nothing can be more obvious, than the decided advantage which this stove possesses over all others, and nothing remained for its improvement but to give its different parts their proper proportions, and to vary its construction, so as to admit of its easy management in domestic use. By the former improvement, a larger quantity of air is admitted in proportion to the fuel consumed, and of course at a lower temperature. The advantages which result from this improvement will be obvious. The ventilation of the rooms warmed by it, is much more complete from a greater quantity of air being admitted; the temperature is more uniform, from the air being more dispersed ; and, lastly, from the air being heated by a greater surface at a lower temperature, the apparatus is not in the least degree injured by the fire, and hence there does not appear to be any limit to its durability.

Nothing can be more vague and uncertain, than the opinions which have been formed of the different apparatus used for warming rooms by heated air. It has in consequence appeared to me a desideratum in inquiries of this nature, to be able to ascertain the power and merits of a stove, as we do those of an engine. For this purpose, my first object was to get an instrument capable of measuring the velocity of currents. After trying a variety of methods, I have found one with which I am perfectly satisfied. It consists of a very light brass wheel, in the form of that for the first motion of a smoke-jack. An endless screw upon the same axis gives motion to a wheel of fifty teeth, on the axis of which is an index, which is watched by the eye, when the instrument is exposed to the current. The wheel acted on by the current, is about two and a half inches in diameter, and the vanes or sails are eight in number, and fill up the whole circle, when their faces are parallel to the plane of their motion, and they are adjusted to an angle of 45°. Under these circumstances, I have found that fifty re

volutions of the first motion take place, while the current causing those revolutions moves through forty-six feet.

In order to ascertain the power and merits of a stove, I generally take a period of twelve hours, beginning with a good fire, and leaving off with the same. During this time, the velocity and temperature in the main warm air-flue should be taken every half hour, and then the average of each taken, keeping an account of the coal consumed in the same time. The temperature of the outer air being also known, the excess of the average temperature above the atmosphere is the datum required.

From the average velocity, the number of cubic feet of air passing through the flue in the twelve hours may be known. Put A = The number of pounds of air heated in twelve hours, allow

ing 14 cubic feet of air to one pound. T= The excess of temperature above that of the atmosphere. W = The weight in pounds of coal consumed in the same time.

= E The effect of the stove, which, in stoves of all sizes on the

same construction, should be generally a constant quantity: Since A the quantity, and T the excess of temperature, are

advantages to be produced by W the weight of coal. E, the effect, will be directly as A and T, and inversely as W.

AT Therefore, E

W To give an example in practice :-A stove which is capable of warming 100,000 cubic feet of space to 60° in the coldest season, when placed at the depth of nine feet below the level at which the warm air is discharged, will furnish about 45 cubic feet every second, raised 60 degrees above the temperature of the atmosphere. To keep up this current and excess of temperature for twelve hours, it will consume not more than three bushels of coals, or 252 pounds. In this case, 49 cubic feet of air in each second will be 1,944,000 in twelve

138,857 X 60 hours, equal to 138,857 pounds. Hence E =

32,930.

252 This number may be taken as a constant quantity, expressive of the power of any stove; but it also expresses the weight of air in pounds, which one pound of Newcastle coal heats one degree of Fahrenheit's thermometer.

This number will not be strictly a constant quantity, as small stoves will not act quite to the same advantage as larger ones; and local and other circumstances will in some degree alter the result of experiments made in the manner above stated. This is more especially the case, when the admission of cold air and the discharge of foul air, are in any degree influenced by the wind.

The cold air is generally brought directly from the atmosphere; and, therefore, as its progress along this channel is affected by the wind, a greater or less quantity will pass through the stove. If the air be deficient, less heat is carried off from the heating surface, and a greater proportion goes up the chimney, on the contrary, when the wind blows into the cold air-flue, the two forces conspire, more air is admitted, more heat is carried off with the air, and of course less is wasted up the smoke-flue.

In all situations where it is practicable, I use an effectual means of regulating the admission of cold and the escape of foulair, by placing at the commencement and termination of these apertures a turn-cap or cowl, in which the vanes are so fixed as to let the wind blow into the one, and assist the escape of air from the other. Although this contrivance will always prevent a counter current, which without its use is sometimes the case, it does not prevent unequal quantities of air from entering, according to the strength of the wind. This is not found in practice to be a great inconvenience; for during the most perfect calm, the air admitted by the power of the stove alone, is sufficient for every purpose of warmth and ventilation : whilst with a tolerable fire in the stove when the wind is considerable, the air comes into the rooms at a higher temperature than the rooms require which is at least erring on the desirable side. If the quantity of air admitted under all states of the wind were required to be uniform, the aperture in the turn-cap for cold air might contain a self-adjustment, by the action of which its area would always be in the inverse ratio of the velocity of the wind; by which means equal quantities of air would always be admitted in equal times.

The turn-cap for the escape of foul air is placed at the top of the building, and is made common to the roof. Under this arrangement all the rooms into which the warm air is admitted have each a foul air Aue terminating in the cavity of the

roof. The contents of all the foul air-flues are therefore ultimately discharged at the turn-cap. This arrangement is adopted at the Derbyshire General Infirmary, and at the Wakefield Lunatic Asylum. In the summer season, when the stove is not in action, the ventilation will depend on the wind, which at some periods may not be adequate to that change of air required in hospitals. In such cases I have adopted an additional means of ventilation. Instead of making the foul air turn-cap common to the roof, I have placed it at the top of a cylindrical cavity built in the roof. Into this cavity I bring all the foul air-flues, which also in this case may be smoke-flues, if constructed with brick. I also connect with the same cavity, the stove chimney, and, if possible all the other smoke-flues in the building. By this means, it may be expected, that some degree of rarefaction in the cylindrical cavity in the roof will be constantly going on, and that hence a perpetual current will be established from every room towards the general outlet. It would be difficult to adapt such an arrangement to old buildings, without great alteration in the roof. But it would be easily introduced into new houses. The advantages derived from it in ordinary dwellings would be very great. In the first place, there could not be an instance of a smoky chimney; in the next, a down current in an unoccupied chimney could not occur, and therefore the passage of the smoke of one chimney down another would always be prevented; and lastly, by having only one outlet for smoke in every house, and that an object which may be made ornamental, we should ultimately get rid of the great deformity which arises from the present appearance of chimneys in buildings.

În all situations where it is practicable to make a cold air-flue, of considerable length under ground, the advantage is well worth securing. I have found by experience that a cold air-flue of fifty yards in length is capable of cooling the air in summer to about an arithmetis

a

cal mean between the temperature of the air and the earth, and a similar advantage is produced by the earth warming the air in the winter season. The shape of the cold air-flue should be such as to present the greatest possible surface; the very contrary being essential to the best construction of flues for the warm air.

These facts will successfully lead to the means of cooling buildings in the tropical climates, and of warming the air when the winter's cold is much below the temperature of the earth.

Great Russel street, Bloomsbury, May, 1821.

FROM THE ANNALS OF PHILOSOPHY.

Black Urine. It appears from Dr. Marcet's paper in the Medico Chirurgical Transactions, that he has met with some cases, in which black urine had been voided. At the request of Dr. Marcet, some was examined by Dr. Prout, who gives the following account of its chemical properties :

The residuums obtained from this urine by evaporation, not only does not contain any lithic acid, as was observed by Dr. Marcet, but no urea can be detected in it by the tests which indicate its presence.

Although the addition of dilute acids produced no immediate change of colour in the urine, yet, on standing for some time, a black precipitate slowly subsided, leaving the supernatant fluid transparent, and but slightly coloured.

The black precipitate thus obtained, was found to be nearly insoluble either in water or alcohol, whether hot or cold. It readily dissolved in cold concentrated sulphuric and nitric acid, forming a deep brownish black solution; but, on diluting the acids with water, the black substance appeared to be again precipitated unaltered. These acids, however, by the assistance of heat, apparently decomposed it. The black substance readily dissolved in the fixed alkalies and in the alkaline subcarbonates, forming very dark solutions. The addition of water did not affect these solutions; but acids re-precipitated the substance apparently unchanged. When ammonia was employed as the solvent, and the excess expelled by evaporation to dryness, a black or deep brown residuum was obtained, which appeared to be a compound of the black substance with ammonia, and possessed the following properties :

It was very soluble in water; and, on being heated with caustic potash, it gave off the smell of ammonia. The black compound, however, did not appear to have any tendency to assume the crystalline form.

In evaporating to dryness, on a piece of glass, the ammoniacal solution in which the black substance had been dissolved, the residuum split into most minute fragments, having a regular and very peculiar appearance, especially when examined with a magnifier.

From the solutions of this compound in water, muriate of barytes and nitrate of silver produced copious brown precipitates, as did also proto-nitrate of mercury and nitrate of lead; but oxymuriate of mercury produced no immediate precipitate, and that obtained from acetate of zinc was of a paler brown colour.

From these experiments Dr. Prout concludes, that the remarkable specimen of urine in question, owes its black colour to a compound of a peculiar principle with ammonia, as Dr. Marcet had inferred from his own trials; but he is moreover inclined to think that the black principle itself, such as obtained from the urine by the action of dilute acids, may be considered as a new body possessed of acid properties. From the small quantity of the specimen, however, which could be spared for Dr. Prout's experiments, it was impossible to obtain complete and decisive evidence on the nature of this substance; but it appears to be sufficiently characterized as a peculiar acid, and to bear a closer analogy to the lithic acid, or rather to some of the compounds which it forms when acted upon by the nitric acid, than to any other principle usually found in the urine.

Should this view of the subject be confirmed by farther observations, Dr. Prout would propose to distinguish this new substance, on account of its black colour, by the name of melanic acid.

FROM THE JOURNAL OF SCIENCE,

Purification of Oil.–A method of purifying common fish oil, and rendering it equal to the best sperm oil, by the use of animal charcoal, is described as having been discovered in Denmark. The description is very incomplete, but mentions that beef bones which have been boiled, are made into animal charcoal in a peculiar way. The charcoal is mixed with the oil, and repeatedly agitated for two months, after which it is filtered through several strata of charcoal, and used as soon as made. The quantity of gas evolved by the bones in the operation is considerable, and is used for lighting the manufactory and adjacent buildings. The residuum is mixed with clay for fuel. T'he loss in this process is estimated at 15 per cent., and the gain is equal to 40 per cent., leaving a balance in favour of the discovery of 25

per The peculiar method of making the charcoal, probably consists in not heating the bones too much. It is well known by the animal charcoal makers in London, that if the temperature be raised too high, the charcoal is worth nothing.

cent.

Purification of the Water of the Seine at Paris. There is an establishment in this city (Paris) for purifying for domestic use the water of the Seine, which gives constant employment to upwards of 200 persons. The water is pumped into vessels about 20 feet deep, and as many in width, where it reposes 12 hours. The clear water is then raised into another vessel, whence it flows into long and shallow cisterns, on the sides of which a great number of sponge-filters are placed, and the sponges are renewed every hour. From the sponge-filters it finds its way into square shallow cisterns, each of which has at the bottom a bed of clean Fontainbleau sand, then a bed of pounded charcoal, then another bed of clean sand, and lastly, at top, a bed of coarse river sand (these last mentioned filters are renewed every six hours); and this is the last operation previous to its distribution.- Tech. Rep. i. 316. We apprehend this process would not suit the London taste. VOL. I. No. 1.-Museum,

M