water, the fluid had risen in it above an inch and a half in twelve hours, and in twenty-four had risen two inches and three quarters; during which time the barometer and thermometer had not sensibly altered. In other experiments, vessels of other forms were used, and the water uniformly rose in those having fissures.

When one of these vessels filled with hydrogen was covered by a bell glass, or when the vessels were filled with atmospheric air, oxygen, or azote, instead of hydrogen, no change took place.

M. Dobereiner considers the effect as due probably to capillary action. He suggests that all gases may be considered as consisting of solid atoms of various sizes, envcloped by atmospheres of heat also very different, and that hydrogén, though it has the largest atmosphere of heat, has the smallest atom, and is thus permitted to escape by fissures, which retain the other gases. Probably," he "fissures may be formed which will permit azote to pass, but not oxygen, and others again which will let the oxygen out, but not carbonic acid gas.

66

says,

Another experiment which seems related to this subject, is as follows: A thermometer tube had been drawn out very fine in the lamp, and it being desired to have it filled with alcohol, the point was immersed in that fluid, and the bulb heated until no more bubbles of air escaped; the tube was then cooled, but no alcohol entered. When again heated, abundance of bubbles of air passed out through the alcohol, though when re-cooled no alcohol would enter. Upon examining the tube with a lens, nothing was seen which could prevent the entrance of the alcohol; on withdrawing the tube from the alcohol, the external air entered with a hissing noise. M. Dobereiner conceives that the diameter of the tube was so small that the alcohol could not enter, but only the air which it contained.—Ann. de Chim, xxiv. 332.

MR. PHILLIPS'S LECTURES

ON CHEMISTRY,

At the London Mechanics' Institution. ON Wednesday Mr. Phillips began a course of Lectures on Chemistry, at this Institution. We were very happy to see that his audience was numerous, and listened to his instructions with attention and pleasure. The necessity we are under of going early to press, prevents us at present taking any further notice of the lecture, except saying that it was distinctly delivered, and illustrated by seve ral well performed experiments. In our next Number we shall give a more detailed account of it.

COMBUSTION PROMOTED BY THE POKER. To the Editor of the Chemist: SIR, In answer to the question by a few admirers of " your little Publication," as to the effect of a poker being placed across the fire, allow me to suggest that it may have arisen from the old custom of placing the shovel perpendicularly in front of the grate, the efficacy of which in promoting a more rapid combustion, may, I think, be philosophically explained as follows:The grate being always situated at the lower part of the room, the constant influx of air from the different apertures, such as the doors and windows, must naturally have a descending motion, replacing that portion which, becoming rarified by heat, escapes by the chimney; place, then, any obstruction opposite to the expiring embers, and they are sheltered from the cold descending current, and exposed only to that which must necessarily ascend through the bottom of the grate. I humbly submit this explanation to the judgment of your admiring friends.

Your obedient servant,
CALORICUS.

INVISIBLE-VISIBLE INKS. SYMPATHETIC or secret inks are fluids, which may be written with on paper, and are invisible when

dry or cold, but acquire colour by heating the paper, or by the application of some chemical agent. These phenomena arrested particularly the attention of the old chemists, and accordingly, in their fanciful ways, they called them sympathetic inks. Thus, if letters be traced on paper with muriate of cobalt, the writing is invisible; and by holding it before the fire, the characters speedily assume a green colour, which again disappears as the paper cools. The writing made with this ink may, therefore, at pleasure be made visible or invisible, by alternately warming and cooling the paper, if care be taken not to expose it to a greater degree of heat than is necessary to make the invisible writing legible.

This experiment is rendered more amusing, by drawing the trunk and branches of a tree in the usual manner, and tracing the leaves with sympathetic ink. The tree appears leafless till the paper is heated, when it suddenly becomes covered with a beautiful foliage.

Various theories have been proposed to account for this remarkable change. According to some, it is owing to the moisture of the atmosphere being absorbed that the colour disappears, and when this is driven off by heat, that is restored. But to this opinion it has been objected, that the same effect is produced, when paper, on which characters have been written with this ink, is entirely excluded from the atmosphere, by being introduced into close vessels. According to others, the sympathetic effect of this ink depends on the iron which is combined with the cobalt. Some suppose that the concentration of the solution, which takes place by the action of heat, is the cause of the appearance of the colour; and its dilution, by absorbing moisture from the atmosphere, the cause of its disappearance; while, again, others are of opinion, that it is partially deprived of its oxygen by being heated, and absorbs it again

in the cold, when the colour vanishes. The former explanation appears to be confirmed by the fact, that the characters are rendered visible by confining the paper in a vessel with quick lime or sulphuric acid, either of which attracts humidity powerfully. The green colour cannot, however, be ascribed entirely to the concentration, but is owing to the temperature; for the solution itself becomes green when moderately heated in a close phial, and loses this green colour as it cools; nor is it easy to explain how the temperature produces this change of colour. Mr. Hatchett has suggested, that it may operate by causing a "temporary difference to take place in the proportion of oxygen existing in the acid menstruum and the oxide;" and it is not impossible, that a high temperature may enable the metal to attract a small portion of oxygen from the acid, which acid may again separate from the oxide when the temperature falls.

The sympathetic ink is prepared in the following manner :-Put into a matrass one part of cobalt or jaffre, and four of nitro-muriatic acid; digest the mixture, with a gentle heat, until the acid dissolves no more cobalt; then add muriate of soda, equal in quantity to the cobalt employed, and four times as much water as acid, and filter the liquor through paper.

MR. COOPER'S APPARATUS FOR THE ANALYSIS OF ORGANIC PRODUCTS.

(Abridged from the Transactions of the Society for the Encouragement of Arts. Vol. xli.)

THE very great interest which is now felt in the various parts of Europe, in the analysis of animal products, and the curious results which have been obtained, particularly in France, by prosecuting this analysis, makes every contrivance for performing it with accuracy of considerable value. Of late years, numerous methods have been suggested by scientific Chemists for this purpose, all of which, even when they possess great merit, are liable to some objection. Mr. Cooper has, therefore, suggested another contrivance, an account of which we shall now present to our readers:

Fig. 1, a a and b b, two long spirit lamps, each having ten burners and wicks, the burners of each lamp sloping towards those of the other, as seen in the end view, Fig. 2; they are placed in a tin

tray, cc, mounted on four feet; this tray is perforated in the middle the whole length of the lamps, and as wide as e e, Fig. 2. The object in making the burners sloping is, that they may clear the lamps and approach each other as near as requisite, and yet leave a clear current of air to the flames, and the tray is perforated and mounted on feet to admit this current.

dd are springing wires, placed at each end of the tray to receive the tube ff, which contains the substances to be analysed, and to hold it over or between the two rows of flames; by pressing the finger and thumb on the two shoulders, gg, Fig. 2, the wires open to receive the tube, and close on letting go; and should the tube be shorter than the lamps, an additional support is placed through the opening, ee, of the tray to rise between the flames, and hold the end of the tube; the tubes are hermetically sealed at one end, and the materials put in while the tube is straight; it is then bent at the other end to suit the mercurial trough.

The tubes are coated with copper foil, wrapped spirally round them; if each succeeding fold lie on half the other, there will be a double coat of copper all the way; if it lie on two-thirds, there will be three layers of copper, and so on; by which the glass tube is support cd from bending when hot, and becomes very uniformly heated. The spirals are continued beyond the end of the tube, to reach the support, and leave the end within the flames. The dotted lines at h, of the second tube, show the end of the tube, short of the support; the foil is secured at the last coil by binding wire, as at i

The third, or uppermost tube, shows the foil in act of being wrapped on, also the proportion of the space occupied by the materials; first, the mixture of oxide of copper with the material to be analysed; next, pure oxide of copper, or copper filings; and lastly, asbestos. When the quantity of water formed is considerable, the tube is either blown into a bulb, or melted on to one ready prepared.

As the wieks nearest the trough are to be lit first, and the remainder in succession, as the former finish their action, there are upright supports of tin, oo, fixed on the lamps, one for each space between the burners, against which to rest a slip of tin, pp, to prevent the lighted wicks from kindling those next, and it also enables the experimenter to blow out those that have done their duty. In Fig. 2, the tin slip, pp, is shown by dotted lines, reaching from lamp to lamp; little flat caps are put on each burner when done with, to prevent the waste of spirit.

It will be known to our readers, that oxide of copper is now extensively employed in the analysis of animal products; it is the instrument also which Mr. Cooper recommends. The oxide of copper (he says) used in the experiments is best procured from the residuum of verdigris, (binacetate of copper) which is or was used to be distilled in glass retorts for the

preparation of strong ascetic acid. The reason I prefer the oxide of copper prepared by this process over any other is, that it is more likely to be free from impurity than that which is prepared by precipitation from acid solutions. Should it, however, happen that at any time such an oxide is not readily to be procured, the oxide that is obtained by heating copper plate and quenching it in water may be substituted, although I give the decided preference to the former, on account of its mechanical texture being much more porous, and consequently exposing a larger surface to the action of substances in vapour passing through it; neither is it so likely to choke up the tube and endanger its bursting, and of course causing a failure in the experiment. Supposing the residuum above mentioned to be employed, it is requisite to expose it to a red heat for twenty minutes or half an hour, to destroy the carbonaceous matter that invariably accompanies it; it should then be pulverized and sifted through a fine wire sieve; that portion which has passed the sieve being again sifted through a finecy press or lawn sieve, the finer dust is got rid of, and each of these portions may be separately kept, and is applicable to different purposes.

A tube of hard glass, either of crown or green bottle glass, being selected about 14 or 15 inches long, and from one to two-tenths of an inch internal diameter, clean the inside from dust by passing through it a piece of cotton, then make it as hot, from end to end, as the fingers can conveniently bear, and draw air through it into the mouth (but not blow through it) while it is still hot, to ensure its perfect freedom from adhering moisture on its inside, and while still warm seal up one end with the blow-pipe ; the tube may be now balanced, but it is necessary in this, as in all other operations of analysis where very small quantities are concerned, that the beam should be affected by 1-200 or 1-300 of a grain, even when loaded with 400 er 500

grains at each end. The substance intended for analysis is now to be introduced into the tube; if it be solid, as for instance camphor or a like substance, it may be broken into small fragments and shaken down to the bottom; if it be a fluid, as a volatile or fixed oil, it may be introduced by means of a small funnel, which is prepared, on the instant, from a piece of flint glass tube of convenient size and substance by heating it near one of its extremities, and suddenly drawing it out. It is evident the semifluid glass will be thus elongated, and a funnel, with nearly a capillary tube, and of any required length, may be obtained. A very little practice will render this part of the business very easy to be accomplished; the funnel is to be put into the tube, reaching very near its bottom or sealed end, and the fluid matter introduced without soiling the upper part of it; care must also be taken, on withdrawing the funnel, that no portion of the fluid is attached to its lower extremity, or otherwise this will happen. The volatile substance, or that which is capable of being rendered so by a red heat, being now introduced into the tube, its weight is to be very carefully taken, which, when done, the oxide of copper, freed from its fine dust by the lawn or cypress sieve,† and recently heated red hot, is to be poured into the tube, to the length of eight or ten inches, having previously put into the tube as much only of perfectly cold oxide as will absorb the fluid portion of matter, and stand about the same height above the solid substance. Having proceeded thus far, a quantity of recently ignited asbes

The balance I have been in the habit of using was made for me by Mr. Robinson, and is sensibly affected by 1-400th of a grain, when loaded with 1000 grains at each end.

+ The finer portion is taken from the oxide to allow more freedom of passage for the vapour through it; in some cases the rush of gas is so sudden, was it not for this precaution, it would be likely to burst the tube.

tos, or spun glass, (the former is the best) is put lightly into the tube, so as to occupy an inch or two, depending on the quantity of water that is expected to be formed. The tube is now to be bent, as represented in Fig. 1, and its weight may be again taken; it is then to be covered with thin sheet copper, and placed between the forceps, as represented in the same figure, with its open extremity inserted under a jar in the ordinary mercurial pneumatic trough, or it may be connected with a gasometer of Mr. Pepys's construction, which, when ten or twenty grains of a substance are employed, and the quantity of either carbon or azote it contains is considerable, is convenient. Small mercurial graduated jars may be used, even if very large quantities of gas are obtained, as the process of decomposition may at any time be stopped almost instantaneously,* and the quantity contained in them being registered, they may be alternately filled with mercury and displaced by the gaseous products, as long as any comes over, reserving only the last portions for examination, of which a few cubic inches alone are requisite.

The lamps being trimmed with very short wicks, are now to be lighted, lighting those first that are nearest the gasometer, and when the tube is red hot, the remaining ones may be set fire to in succession, until the whole length of tube that is filled with the oxide is red hot. One set of lamps for a tube, of the size I have mentioned above, is generally sufficient; but should tubes be used of larger size, snch as half an inch in diameter, both sets will then be required. In coating the tube with sheet copper, care must be taken not to cover that part of it which contains the asbestos, otherwise the heat will be conducted by it to that portion of tube, and prevent the condensation of the vapour of water, which is very essential. In the analysis

I consider this as one of the advantages of this apparatus.