withheld them from the public eye, or put them forth in a more modest form. For this he is blameable, and for this he should have been censured; but there are marks of genius in his hasty production, sufficient to have redeemed it from unsparing and unqualified censure. There is one chapter devoted exclusively to the blow-pipe, which Mr. Gurney has been at considerable pains to improve. This chapter and Mr. Gurney's improvements are passed by in the Review without any other notice than stating there is such a chapter. We may be mistaken, but we consider the instrument as improved by Mr. Gurney, much safer than before, and shall take an early opportunity of submitting an account of these improvements to readers. our CHEMISTRY AS A SCIENCE. Art. IV. CHLORINE. THE Substance now known by the name of Chlorine to Chemists, was, up to the year 1810, called by them oxymuriatic acid. The latter name was given to it on the supposition that it was a compound substance, consisting of muriatic acid and oxygen. A different opinion was first formed, perhaps about the year 1808, but it was in 1810 that Sir Humphrey Davy published his account of the experiments he had made on this substance, whence the conclusion was drawn that it was a simple substance, to which the name of Chlorine was given, from its yellow colour. Since that time, the great majority of Chemists have adopted the views of Sir Humphrey Davy, and chlorine appears in most of the elementary treatises on Chemistry as a simple substance, classed along with oxygen, either from its electrical property, or from its being a supporter of combustion. In papers like these, intended only to give an outline of the most general and best established facts of the science under an arbitrary arrangement, and to show, as well as we can, the relation of these facts to one ano ther, and the mrtual dependence and connexion as a whole, we cannot enter at all into the discussion of the question, whether chlorine be or be not a simple substance. We are bound, however, to remark, that many eminent Chemists, in different parts of Europe, still adhere to the opinion, that chlorine is a compound substance. Nor can we give, on the present occasion, even an outline of the many nice and delicate experiments made to decide the point, and of the fine and subtle theories which have been advanced on both sides of the question. Consistently with the purpose we have in view, we must confine ourselves to remarking, that Sir Humphrey Davy being unable to obtain any oxygen from this substance by exposing it to the action of charcoal heated to whiteness, which in this state has a great avidity for oxygen, concluded it contained none; and having afterwards subjected it to a great number of experiments, with a view to decompose it, and being unable to obtain any other product but it as long as it was perfectly dry, he concluded that it was a simple substance. His opponents say that the presence of water being necessai to the existence of muriatic acid, as long as there is none present the oxymuriatic acid will not give up its oxygen, but that wherever water is present muriatic acid is formed, and oxygen evolved. At any rate, chlorine must be considered as a simple substance only in the strict chemical meaning of that term, viz. it has not been decompounded. Oxygen gas, we have seen, performs a most important part in all the phenomena of life; and in many of the changes which constantly take place in unorganized substances. Chlorine, on the contrary, is solely a product of art; it enters into no important natural combinations, except that of common salt; it is not necessary for the continuance of existence, and, except as it has been applied to some useful purposes in the arts, it seems of little importance in the economy of nature. Admitting, therefore, on the single chemical ground of art never having yet decomposed it, that it is a simple substance, it does not at the same time possess any of those grand characteristics which lead the mind to rely, as in the case of oxygen, on the Chemist's analysis, and to believe that here he has really discovered an element of nature. Chlorine is obtained in the following manner :-Put into a small glass retort a quantity of the black oxide of manganese in powder, and pour over it as much of the common muriatic acid, which is to be got in all Chemists' shops, as will make the whole into a thin paste. Plunge the beak of the retort into the pneumatic trough, under a stout glass phial filled with water, as already described, and apply the heat of a common lamp to the bottom of the retort. A gas rises which displaces the water in the phial, and this gas is chlorine. It was discovered by Mr. Scheele, the celebrated Swedish Chemist, about the year 1774, and was by him considered to be muriatic acid, deprived by heat of an imaginary substance, called phlogistion, and hence named de-phlogisticated muriatic acid. On the French theory of Chemistry growing into fashion, it was considered as a compound of muriatic acid and oxygen, and therefore called oxymuriatic acid. As we have already stated, since the experiments of Sir Humphrey Davy, it has been supposed to be a simple substance, and under this supposition it is called chlorine, from its peculiar colour. It is a gaseous body, possessing all the mechanical properties of common air, Its colour, which is hardly perceptible by candle-light, is greenish yellow. Its taste is astringent. When breathed, mixed with atmospheric air, it produces a most insufferable sensation of suffocation, occasions violent coughing, with much spitting, followed by great debility, and if breathed in its pure state it destroys life almost instantly. It is two and a half times as heavy as common air, its specific gravity being 2.500, taking that of common air as 1000. It possesses the very peculiar property of destroying all vegetable colours, and of rendering most substances white. This property has led to its employment as an agent in bleaching, and by it most of the cloths now manufactured in this empire are made of their dazzling whiteness. Mr. Scheele first observed this property in chlorine; M. Berthollet, a French Chemist, first recommended its employment in bleaching; and the celebrated Mr. Watt, of Birmingham, was one of the first persons to introduce it into Great Britain. Though chlorine will not support life it supports combustion. A candle burns in it with a low red flame, emitting much smoke and little light. Phosphorus, antimony, arsenic, zinc, iron, and several other metals take fire when plunged into chlorine, and burn with considerable splendour. In these cases the gas diminishes or disappears, and the combustibles are converted into new substances, which are considered as compounds of them and the chlorine, and have received the name of Chlorides. Water absorbs a quantity of this gas equal to twice its own bulk; and the water acquires the colour, smell, taste, and whitening properties of the gas itself. The electric property of chlorine, viz. that of being deposited at the positive pole of the galvanic battery, has already been mentioned as the only characteristic which has made us place it here. It combines with various other substances; but we shall postpone till a later period all remarks on compound substances. In our next paper we shall describe Iodine, and say what can be said of Fluorine. TO RENDER BODIES LUMINOUS IN THE DARK. Ir a four or six ounce phial, containing a few ounces of liquid phosphorus be unstopped in dark ness, the vacuous space in the bottle emits a sufficient light for showing the hour of the night by holding a pocket watch near it. When the phial is again corked, the light vanishes, but reappears instantly on opening it. In cold weather, it is necessary to warm the bottle in the hand before the stopper is removed: without this precaution it will not emit light. Liquid phosphorus may likewise be used for forming luminous writings or drawings: it may be smeared on the face or hands, or on any warm object, to render it luminous; and this is in nowise hazardous. If rubbed on the face, taking care to shut the eyes, the appearance is most hideously frightful; all the parts appear to be covered with a luminous lambent flame, of a bluish white co lour, while the mouth and the eyes are depicted as black spots. This luminous appearance is a real, though slow combustion of a very minute portion of phosphorus presented to the air, which is partly wafted away in luminous vapours, and partly converted into phosphoric acid. The bottle containing the liquid phosphorus must be kept in the dark, because light decomposes the solution of phosphorus. TO MAKE A FINE GREEN A GIVEN weight of verdigris is to be dissolved by heat in a copper vessel, in a sufficient quantity of pure vinegar, and then an aqueous solution of an equal quantity of white arsenic added. Generally a dull green precipitate falls, which must be re-dissolved by adding more vinegar. The mixture is then to be boiled, and after some time, a crystalline precipitate appears, of the finest green colour, which, separated, washed, and dried, is the substance in question. If the liquor still contains copper, arsenic is again to be added; or if it contains an excess of arsenic, the preparation of copper must be added, and the process carried on as be fore. Sometimes the liquor contains an excess of acetic acid, and may then be employed to dissolve verdigris, as at first. CURE FOR DRY ROT. TAKE two ounces of white arsenic in powder; dissolve it by boiling it in one gallon of soft water. If boiled in an iron or tinned vessel, add half an ounce of copper filings, but if in an untinned copper vessel, the filings are not necessary. To a quart of size and half a pound of common tar, add a small quantity of fresh slaked stone-lime, sifted pretty fine; beat them well into a paste, which should be then nicely dissolved with the above solution, gradually adding, during the process, (by small portions) as much more of the pulverized lime as will give the whole a proper (rather diluted) body, to be laid on with a painter's brush. New work when finished, as a preventive, should be dressed with the composition at least twice, after well drying the first coat. Old work, as a curative, when removed and repaired, (such as diseased wainscot,) should be perfectly dried by exposition to the air, and then well dressed on its back before it is returned to its place. VEGETABLE ALKALI IN HORSE-CHESNUTS. THE experiments of Messrs. Pelletier and Caventon on quinina, and the results they obtained, induced M. Francesco Canzoneri, of Palermo, to make a similar course of experiments on the fruit of the horse-chesnut, (esculus hippocastanum) which has been sometimes successfully employed as a febrifuge. By following the means they recommend, he obtained a peculiar substance from this fruit, which he has named esculine. Five pounds of the fruit, dried and pulverised, were treated with 80 pounds of water, rendered sour by sulphuric acid. The decoction allowed to cool, and lime being added, till a slight alkaline quality was produced, deposited a flaky precipi tate of the colour nearly of lemons. Washed, dried, and reduced to powder, this precipitate was exposed to the air, to facilitate the action of the carbonic acid on the lime. It was then digested with 30 pounds of alcohol, at the temperature of 90° for half an hour; and this operation was frequently renewed. The liquor was filtered and re-distilled, to recover as much as possible of the alcohol. The remainder evaporated to dryness, left the esculine behind. It is an amorphous mass, of a sweetish and very pungent taste, soluble in alcohol and ether; exposed to heat, the matter swells and burns in a manner analogous to oil. The author classes this substance with the other vegetable alkalies lately discovered. BLEACHING SUGAR. Ir is announced in a French journal, that chlorate of lime, which is now so extensively employed in bleaching linen, may also be successfully applied, both in its gaseous and liquid state, to bleaching sugar. As the gas is formed, it is conveyed into a solution of sugar previously filtered, and its absorption is promoted by agitating the sugar. When the colour which is required is obtained, the liquor is filtered over lime to separate the muriatic acid, and then over a preparation of animal carbon. Immediately after the filtration, the syrup is concentrated by the usual method. The gas may also be applied to sugar already crystallized, by spreading it over shelves, made altogether of wood, or of hair cloth, and placed round an apartment, into which the gas is conveyed as it is produced. The sugar is spread out on very thin layers, and is sometimes stirred by means of rakes. The sugar must afterwards be exposed to the action of lime to separate the excess of muriatic acid. The liquid chlorate may also be employed, by adding it to the filtered syrup, in the proportion of one-fifth, and agitating the mixture, then boiling it with animal carbon, filtering, and again agitating with another dose of chlorate, amounting to the sixth part of the whole. These operations are again repeated with the chlorate, in the proportion of a tenth part, and the syrup is finally filtered, and it passes clear and transparent like water. In the second mode of application, the animal charcoal is first added, and then the chlorate, after which the same agitation and filtering, as above described, is again to take place. The chlorate may also be employed to bleach molasses, so that it may be used on several occasions, when it is now rejected in consequence of its colour. The author gives no estimate of the advantages of employing the chlorate of lime, and, therefore, we are quite unable to say, whether his method is an improvement or only a novelty. OIL FOR CLOCKS, WATCHES, WITHIN a few years, a M. Chevreul has devoted a great portion of his time to the analysis of animal substances, and has made some remarkable and valuable discoveries. It results from his investigation, that all fat is composed of two distinct substances: one of which, called elain, remains fluid at the ordinary temperature of the atmosphere; the other, called stearine, easily becomes solid. The former should be used for all instruments of a delicate nature, to which oil is applied, to prevent friction. It is thus obtained: oil or fat is exposed to the action of eight times its own weight of alcohol, nearly boiling ; the liquid is then poured off, and, on cooling, the stearine separates in crystals. The alcohol is then evaporated to the fifth part of the volume of the whole, and the elain remains, which is colourless, insi-` pid, without smell, and difficult to congeal. Or, by squeezing tallow between the folds of porous paper, the elain is separated, and soaks into the paper, while the stearine remains behind. The paper being then soaked in water, and pressed, gives up the elain. BLEACHING. MODES FORMERLY IN USE. THE first requisite to good bleaching was a favourable situation; and the gentle slope of hill, with a southern aspect, or a valley with a stream passing through it, was, in general, chosen for the purpose. A large supply of water is always indispensable; and the bleachinggrounds of Holland, and of other countries, when formed on the Dutch model, were intersected at right angles with numerous canals, at such a distance from each other, that a workman with an ordinary scoop, such as is used to throw water over the sails of a vessel, might easily wet all the linen lying on the space enclosed between the canals. Great care was taken to keep this water clean; and in Holland, where the flat nature of the country permits no running streams, and where the sluggish water rather stagnates than flows, the canals were themselves frequently cleaned out. They were provided with sluices, and tubs set in the earth at the corners, so that the water could always be drawn off at pleasure. Much of the superiority of the Dutch mode of bleaching arose from the cleanliness of that people,. and the great care they take in all trifling matters. The object of all bleaching is the same; but as the colouring matters are different in different substances, it requires different processes to extract these matters, as the substance to be operated on is linen, cotton, silk, or wool. It would take up too much of our space to describe them all; and, therefore, in the little notice we are now to give of the former mode of bleaching, we shall confine ourselves to linen. The colouring matter to be extracted from linen is supposed to be of a resinous nature; for, we must say, that, as yet, this point has not been precisely determined. It is known, however, that the quantity to be extracted from linen is much greater than that to be extracted from cotton; and hence, the process is longer and more expensive. It has been rendered pro |