Part 32 (1/2)

Froed to confine myself to experiments upon very small quantities of alkohol, or at least to combustions made in open vessels, such as that represented in Pl IX

Fig 5 which will be described in Section VII of this chapter If I am ever able to reation

SECT VI

_Of the Combustion of Ether_

Tho' the combustion of ether in close vessels does not present the same difficulties as that of alkohol, yet it involves some of a different kind, not ress of my experiments I endeavoured to profit by the property which ether possesses of dissolving in at it inflammable without explosion For this purpose, I constructed the reservoir of ether a b c d, Plate XII Fig 8 to which air is brought froazometer by the tube 1, 2, 3, 4 This air spreads, in the first place, in the double lid ac of the reservoir, froh, ik, &c which descend to the bottoazoh the ether in the reservoir We may replace the ether in this first reservoir, in proportion as it is dissolved and carried off by the air, by means of the supplementary reservoir E, connected by a brass tube fifteen or eighteen inches long, and shut by a stop-cock This length of the connecting tube is to enable the descending ether to overcome the resistance occasioned by the pressure of the air froazometer

The air, thus loaded with vapours of ether, is conducted by the tube 5, 6, 7, 8, 9, to the jar A, into which it is allowed to escape through a capillary opening, at the extremity of which it is set on fire The air, when it has served the purpose of coh the bottle 16, Pl XI the worm 17, 18, and the deliquescent tube 19, 20, after which it passes through the alkaline bottles; in these its carbonic acid gas is absorbed, the water for been previously deposited in the former parts of the apparatus

When I caused construct this apparatus, I supposed that the combination of atmospheric air and ether for 8 was in proper proportion for supporting combustion; but in this I was mistaken; for there is a very considerable quantity of excess of ether; so that an additional quantity of atmospheric air is necessary to enable it to burn fully Hence a lamp constructed upon these principles will burn in coen necessary for combustion, but will not burn in close vessels in which the air is not renewed Fro lighted and shut up in the jar A, Pl XII Fig 8

To re atmospheric air to the lamp by the lateral tube 10, 11, 12, 13, 14, 15, which I distributed circularly round the flaly rare, that it is blown out by the gentlest possible strea ether I do not, however, despair of being able to accoes I am about to have made upon this apparatus

SECT VII

_Of the Coen Gas, and the Formation of Water_

In the foren, which are both in the aeriform state before combustion, are transformed into liquid or water by the operation This experiment would be very easy, and would require very siasses perfectly pure, so that they ht, in that case, operate in very sasses in proper proportions, ht continue the combustion indefinitely But, hitherto, cheas; from which circumstance, they have only been able to keep up the coas for a very limited tias is continually increasing, the air becooes out This inconvenience is so as employed is less pure From this circu upon small quantities, or et rid of the residuuas; but, in this case, a portion of the water for the experi error is the erous to the accuracy of the process, that we have no certainit

These considerations make me desirous to repeat the principal experias entirely free froas; and this as extracted from this salt does not appear to contain azote, unless accidentally, so that, by proper precautions, it may be obtained perfectly pure In the mean time, the apparatus eas, which is described in the experiment for recomposition of water, Part I Chap VIII and need not be here repeated, will answer the purpose; when pure gasses are procured, this apparatus will require no alterations, except that the capacity of the vessels5

The coun, continues for a considerable tiradually, in proportion as the quantity of azotic gas re froas is in such over proportion that the cooes out This spontaneous extinction as is pressed upon in its reservoir, by an inch and a half of water, whilst the oxygen gas suffers a pressure only of three lines, a mixture of the tould take place in the balloon, which would at last be forced by the superior pressure into the reservoir of oxygen gas Wherefore the co the stop-cock of the tube dDd whenever the flarows very feeble; for which purpose it must be attentively watched

There is another apparatus for coh we cannot with it perform experi instru results that are extremely proper to be shewn in courses of philosophical che 5 contained in a metallic cooller ABCD To the upper part of this worm E, the chimney GH is fixed, which is composed of two tubes, the inner of which is a continuation of the worm, and the outer one is a case of tin-plate, which surrounds it at about an inch distance, and the interval is filled up with sand At the inferior extrelass tube is fixed, to which we adopt the Argand la thus disposed, and the la filled with a determinate quantity of alkohol, it is set on fire; the water which is for condensed in the worm, runs out at its extremity F into the bottle P The double tube of the chimney, filled with sand in the interstice, is to prevent the tube fro the water; otherwise, it would fall back in the tube, and we should not be able to ascertain its quantity, and besides it uish the flame The intention of this construction, is to keep the chimney always hot, and the worm always cool, that the water , andpart of the apparatus By this instrument, which was contrived by Mr Meusnier, and which is described by me in the Memoirs of the Academy for 1784, p 593 we may, with attention to keep the worm always cold, collect nearly seventeen ounces of water from the combustion of sixteen ounces of alkohol

SECT VIII

_Of the Oxydation of Metals_

The ternify the process by which ree of heat are converted into oxyds, by absorbing oxygen froen possessing a greater affinity to metals, at a certain teed in its free state; but, as this disengageressive, it is scarcely evident to the senses It is quite otherwise, however, when oxydation takes place in oxygen gas; for, being produced with enerally accoht, so as evidently to show that metallic substances are real coree of affinity to oxygen Gold, silver, and platina, for instance, are incapable of taking it away froreatest known heat; whereas the other er or sen, and of the latter to caloric, are in exact equilibrium Indeed, this state of equilibriueneral law of nature in all combinations

In all operations of this nature, the oxydation offree access to the air; it is so the action of a bellohich directs a streareatly as be used, which is readily done by azometer formerly described The metal, in this case, throws out a brilliant flame, and the oxydation is very quickly accomplished; but this method can only be used in very confined experias In the essay of ores, and in all the common operations of the laboratory, the calcination or oxydation of metals is usually perfor 6

co furnace The substances to be oxydated are frequently stirred, on purpose to present fresh surfaces to the air

Whenever this operation is perfor flies off into the surrounding air during the process, the ht; but the cause of this increased weight during oxydation could never have been discovered by means of experiments performed in free air; and it is only since these operations have been performed in close vessels, and in determinate quantities of air, that any just conjectures have been for the cause of this phenomenon The first method for this purpose is due to Dr Priestley, who exposes the11 placed upon the stand IK, under a jar A, in the bason BCDE, full of water; the water isout the air with a syphon, and the focus of a burning glass is made to fall upon the metal In a few en contained in the air combines with the metal, and a proportional diminution of the volu as, still however iven an account of a series of experiments made with this apparatus in my Physical and Chemical Essays, first published in 1773 Mercury may be used instead of water in this experiment, whereby the results are rendered still more conclusive

Another process for this purpose was invented by Mr Boyle, and of which I gave an account in the Memoirs of the Academy for 1774, p 351 The20 the beak of which is hermetically sealed; the reat precaution The weight of the vessel, and its contained substances, is not at all changed by this process, until the extremity of the neck of the retort is broken; but, when that is done, the external air rushes in with a hissing noise This operation is attended with danger, unless a part of the air is driven out of the retort, by means of heat, before it is hermetically sealed, as otherwise the retort would be apt to burst by the dilation of the air when placed in the furnace The quantity of air driven out may be received under a jar in the pneumato-chemical apparatus, by which its quantity, and that of the air re in the retort, is ascertained I have not multiplied my experiments upon oxydation of metals so much as I could have wished; neither have I obtained satisfactory results with any metal except tin It is much to be wished that some person would undertake a series of experiasses; the subject is important, and would fully repay any trouble which this kind of experiht occasion