of substances containing much hydrogen, and especially when ten or twelve grains of them are taken, it will be found convenient to attach to the tube a small bulb, to contain the water that is generated.

If the substance be a vegetable salt, it must be freed from all extraneous moisture; this is best effected by suffering it to remain over an hygrometric substance in vacuo for some time.

Those who have not the convenience of an air-pump, may operate in this way: A wide-mouthed phial, provided with an accurately ground stopper, being procured, select another and much smaller phial, that will easily go into it; strew on the bottom of the larger phial a quantity of chloride of calcium, (dry muriate of lime) put into the smaller phial the substance in fine powder intended to be dried, and place this in the larger phial standing on the chloride; moisten a small piece of bibulous paper with alcohol, and put it into the larger phial, but not inside of the smaller one; when thus arranged, set fire to the moistened paper, and when it has burned a second or two put the stopper in its place, and take care that it is perfectly tight; a very good vacuum is by this means formed, and the process of dessi cation goes on rapidly.

The substance in this state is to be mixed with a portion of the oxide recently ignited, but in this case suffered to cool, then as quickly as possible introduced into the tube. As much of the oxide may be used as would occupy an extent of tube equal in proportion to that shown in the upper tube; a quantity of oxide is then to be put upon the mixture, and over this it is sometimes well to put a small quantity of copper filings or scrapings; upon these the asbestos is to be used as above, and the operation of ignition is to be conducted in a somewhat different manner to that last mentioned.

The lamps in this case are to be lighted at the extremity next the gasometer, and as soon as the gas

ceases to be liberated, the next in succession may be employed, and so on to the end; but instead of suffering the whole of them to continue in flame, it is as well to extinguish a portion, and to suffer only about three or four to remain in operation at once, but taking care to ignite the whole extent of tube at the close of the process. The gaseous products being collected, and their bulk noticed, their analysis is to be conducted in the usual manner, taking care, however, in all instances, to observe the precise temperature of the gases, that their bulk, as also the quantity of aqueous vapour they contain, may be estimated, and either to equalize the internal and external surfaces of the mercury, or to calculate the volume of gas by the difference of mercurial levels.

CHEMISTRY AS A SCIENCE. Art. VII.

NITROGEN.

Ir a quantity of iron filings and sulphur, mixed together and moistened with water, be put into a glass vessel, and all communica→ tion with the external air be cut off, in the course of a few days a portion of the air will disappear, and the remainder, which, by this process, is incapable of further diminution, is called nitrogen or azotic gas. To render it pure it is agitated with water. If phos phorus be substituted for the iron filings and sulphur, and the temperature remain about 60°, the absorption will be completed in less than twenty-four hours. Or introduce into a wide mouthed glass vessel, placed in the pneumatic trough over water, 100 measures of common air, and about 80 measures of what is called nitrous gas, the mixture will acquire a brownish red colour, a large portion of it will be absorbed by water, and there will remain 79 measures of pure nitrogen. In this case the nitrous gas combines with the oxygen of the air, and forms nitric acid, which unites with the water,

and the azot or nitrogen of the atmospheric air is left behind. This is perhaps the easiest and best method of procuring this gas.

From the quantity of azotic gas remaining in the last experiment, and several other examinations, it is inferred that the atmosphere contains about 79 parts in bulk of azotic gas, nearly all the rest is oxygen gas. Mr. Lavoisier first made azotic gas known to the world as a component part of atmospheric air. The experiments were published in 1773. Scheele had before that period procured azotic gas, and shown that it was a distinct substance, though his treatise on air and fire, in which his analysis is given at length, was not published till 1777. But Dr. Rutherford, of Edinburgh, had procured this gas before either of these philosophers; and even before his time it must have been frequently generated during the operations of Chemists, though then all gases were regarded as common air, having different properties, in consequence of some substances which they held in solution. What is the precise use of this gas in the atmosphere, (and we cannot suppose so large a quantity to be there for no purpose), Chemists have not yet succeeded in discovering. It is certain that only the oxygen of the atmosphere disappears both by breathing and by combustion; but at the same time it has been demonstrated, that to breathe oxygen alone is not permanently healthy. No mixture of gases yet discovered answers so well for the support of animal life as that mixture of which the atmosphere consists, and of which a large proportion is azot; and yet, we repeat, the use of this quantity, and the mode in which it operates are not known. Some persons suppose it serves merely to dilute the oxygen; others that a portion of it is inhaled in breathing; and from some late experiments of Dr. Edwards, a physiologist of some celebrity, this opinion seems highly probable. We do not consider, however, that the present is a proper place to

enter further into this discussion," as our readers, as far as our own labours are concerned, are yet totally unacquainted with one substance which plays an important part in the phenomena of breathing. We shall postpone this part of our subject till a later period, and were only led to allude to it now in order to induce the young Chemist to direct his researches towards this unsuccessfully cultivated part of the field of Chemistry. But though its use in supporting animal life is not exactly known, its noxious property, as far as this is concerned, has been fully ascertained. Animals obliged to breathe it die very soon, precisely as they would do were they plunged under water. The epiglottis, or door of the windpipe, closes spasmodically whenever nitrogen is applied to it, and the animal dies, not so much because azot is present, but because there is no oxygen. From this property of destroying life, the French Chemists called this substance Azot, which is derived from two Greek words, signifying" de structive of life." As this property does not belong to it exclusively, and in fact is possessed more or less by every other gas, its name cannot be considered as well chosen. Some Chemists, therefore, reject this term, and call it Nitrogen, from its being the base of an order of compound substances, some of which are well known, and have long been known by the name of Nitre and its derivatives. It has also been called Corrupted Air, Mephitic Air, and Phlogisticated Air, all of which terms convey an improper idea of its nature. In our present knowledge of this substance, undoubtedly Nitrogen is the most descriptive and most applicable term. However, as Azot is more generally in use than Nitrogen, and was for a short period the only word employed, we shall use both these terms indiscriminately, in order that our readers may constantly recollect they are only different names for the same substance.

Azot has this singularity, that

whenever it unites with those bodies which are called supporters of combustion, no heat and light are emitted. At the same time, a lighted candle, when immersed in it, is instantly extinguished; and if enclosed in a portion of atmospheric air, is also extinguished the instant all the oxygen is consumed. It is, therefore, incombustible in either sense in which this term is used, and for this reason is by some chemical philosophers classed apart from all other substances.

Like common air, it is insipid, inodorous, and invisible, capable of being compressed, and having a constant tendency to expand. It is somewhat lighter than air, its specific gravity being as 969, or, according to some authors, as 972 to 1000. It is not perceptibly absorbed by water, unless the water has previously had the air expelled by boiling, when it takes up about a fiftieth part of its own bulk of nitrogen.

Azot is placed by most Chemists among the negatively electrical elementary bodies; but it is asserted by some Chemists, that it is neither positively nor negatively electrical and as oxygen stands at the extreme of one pole, and hydrogen at the other, it has been supposed that azot is not a simple substance, but a compound, in equal parts of hydrogen and oxygen. There are, undoubtedly, several reasons for supposing azot to be a compound substance, par ticularly its formation by the assimilating organs of the body, and numerous attempts have been made to decompose it. Indeed, several distinguished Chemists, misled by some apparent results, have announced to the world, that they had effected this, and that it actually was a compound of oxygen and hydrogen. On these experiments having been repeated, either the same results were not obtained, or they admitted of different explanations. At present, therefore, though there are several reasons drawn from analogy for believing nitrogen a com

pound; and many phenomena, now involved in obscurity, which would admit of an easy explanation, were it so proved, we are bound to admit that no sufficient proof has yet been obtained of azot being a compound. Till some of the readers of THE CHEMIST, stimulated by a wish to improve the science; or some persons, possessing a more powerful instrument of analysis than any yet known, shall decompose azot, we must continue to class it among simple substances. Some of the compounds of nitrogen are very curious, both in their mechanical qualities and in their effects on the animal organs; but we must refer the consideration of these till we treat of compound substances.

TO DISTINGUISH STONES FOR BUILDING, WHICH ARE LIABLE TO BE AFFECTED BY FROST.

MM. LEPEYRE and Vicat, says M. P. Brard, knowing that I had been occupied in the study of mineralogy as applicable to the arts, engaged me in an inyestigation of the means best adapted to distinguish such stones, as, being otherwise fit for building materials, gave way to the action of frost. I found it impossible in this respect to ascertain any thing from their mineralogical characters, and was obliged to follow another course. During the winter of 1819, I carefully examined with a lens the chalky limestone of the neighbourhood of Periguex, and the sandstone of the coal basin of la Vezère, both equally liable to this action; I soon found that each scale of the limestone, and each grain of the sandstone was raised by the re-union of small needles of ice, which, when they melted, suffered the particles to fall and collect about the stone, and that where particles had fallen off in this way, a fresh succession was raised in the same manner, and ultimately separated from the mass.

I was struck by the resemblance of the ice in silky crystals to the

saline efforeseences which appear between the plates of certain shists, and on the surface of old walls. I remembered the effect of common salt on bad pottery, and on the saline rocks of the Tyrol, and conceived the idea of substituting the action of a saline solution to that of common water. After various experiments, I gave the preference to sulphate of soda, its effects being the most constant and most conformable to the action of frost.

The experiment, that it may lead to satisfactory results, should be conducted as follows:-Suppose an excavation newly made into limestone and other rocks, and it be desired to ascertain the liability of the rock to disintegration by the action of frost.

1st. A cube of two inches in the side is to be cut from each part to be tried, the various cubes numbered with thick China ink, and their original sites also marked,

2d. About four pints of common cold water is to be saturated with sulphate of soda, so that a few grains of the salt shall remain undissolved.

3d. This solution is to be heated to ebullition, and then all the cubes to be entirely immersed in it. When the boiling has recommenced it is to be continued for half an hour.

4th. The cubes are to be withdrawn from the solution and placed each one in a saucer, numbered as the cube is; a small quantity of the solution is to be poured on to each cube, and the whole left until covered with white efflorescences perfectly analogous in appearance to the rime or hoar frost, which causes the disintegration of the stones. These efflorescences will appear in about twenty-four hours if the air is dry or hot, but in a humid atmosphere are sometimes five or six days.

5th. When the efflorescences appear on the angles and sides of the

cubes, they are to be dissolved again by means of a few drops of water, or better still with a little of the solution in which the cubes

6th. The specimens to be tried having been washed on all their faces, the detached matter is to be examined, and a judgment formed from it, of the relative qualities of each kind of stone submitted to the proof; for the greater the number of the detached particles collected in the saucer, the more liable is the stone to be attacked by frost; the smaller the number, the more capable is it of resisting cold.

As yet, all the results of this test have accorded perfectly with the effect of time and frost. Such stones as have been found to disintegrate by frost have given way to the salt, such as time has sanctioned have resisted the new agent; so that the mechanical effects of the two are perfectly analogous, Crystallization takes place with both, augmentation of volume, efforts on the surfaces of the small cavities containing the water or solution, and if the aggregation be not sufficiently powerful to resist the action, disruption, and a gradual decay of the rocks either in their natural sites, or if they have been applied to use in their new situations. The action of the sulphate of soda being quite mechanical, is exerted indifferently on all kinds of rocks deficient in aggregation, on limestones, sandstones, large-grained granite, granites of too micaceous a structure, shists, lavas, &c. It may be employed as a proof or test also even upon slates, bricks, tufas, mortars, and cements, as is proved by a table of various results of this kind.

period, good building stones may be re*If the proof be continued for a longer jected, for the prolonged action of the salt is more powerful than that of ice.

CHLORATE OF LIME AS A

MANURE.

M. DUBUC, an Apothecary, at Rouen, has, since 1820, made repeated experiments with chlorate, or oxymuriate of lime as a manure; and has published the following account of the results. A kilogramme of the dry chlorate was dissolved in 60 litres of water (or about one pound to eight gallons), and the earth was watered with it both before and after the plants were put in it or the grain sown. Mr. Dubuc then sowed maize in a light soil, watered eight or ten days before with the solution of the chlorate, and he sowed some other maize in a similar situation and exposed to similar circumstances, but watered with common water. The former, which was watered from time to time with the chlorate, grew to double the size of the latter. He also hastened the growth and increased the size of lilacs, and a variety of other shrubs, by watering with the solution of the chlorate. Onions and other vegetables, which already grow to a large size in the neighbourhood of Rouen, were doubled in magnitude by the action of the chlorate. The large annual sun-flower rose, as in Spain, to the height of 15 and 16 feet, while in ordinary circumstances it only rises to the height of six or eight feet. Some of the branches were from three to four inches in diameter, and the leaves were from 18 to 20 inches broad, the disk of the flowers being from 12 to 14 inches in diameter, and the grains yielded the half of their weight of an excellent eating oil. From the

centre of the flower exuded a transparent volatile oil, verý oderous, and drying easily in the air. M. Dubuc, on May 11th, 1822, planted potatoes of an equal size and weight, in two beds close to each other, being only separated by a walk six feet wide. One of the beds was watered with the chlorate, and the other with water from the cistern; both were dug up in November 1822, and the former had potatoes six inches long, twelve inches in circumference, and weighing more than two pounds; the latter were about half the size and weight of the former. The large potatoes were as good as the small ones, and kept fully as well up to the month of April. They were watered only three times with the solution of the chlorate after they were sown, and their tops surpassed the tops of the others as much as the roots. In general it was suf ficient to water the plants with the chlorate three or four times at considerable intervals.-Ann. de Chim. et Phys. No. xxv. p.214.

SULPHUROUS ACID GAS. M. BERTHIER shows that this gas may be procured pure and abundant in the following manner:— Heat twelve or fourteen parts of sublimed sulphur mixed with 100 parts of peroxide of manganese in a glass retort, and sulphurous acid gas will come over. The residue in the retort is not (as might be supposed) sulphuret of manganese, but protoxide of manganese, mixed with a little sulphate of manganese, and sometimes a little sulphur.Annales de Chimie, xxiv. 275.