that of ammonia by a trihydric model, then the molecule of water must be represented by a dihydric model; thus:

When water is acted upon by metallic sodium, one equivalent of sodium expels one equivalent of hydrogen, to form the well-defined body hydrate of sodium, and the action proceeds no further. But when melted hydrate of sodium, at a temperature approaching that of redness, is acted upon by metallic sodium, a second equivalent of sodium turns out a second equivalent of hydrogen, to produce oxide of sodium. This replacement of the hydrogen of water by sodium at two successive stages, the first stage of replacement taking place at ordinary temperatures, and the second stage at a dull red heat,-is even better defined than the replacement of the hydrogen of ammonia by ethyl at three successive stages, and than the replacement of the hydrogen of marsh-gas by chlorine at four successive stages.

But the formation of ether from water by Williamson's process, affords a still closer resemblance to Hofmann's formation of triethylamine from ammonia. Water H2O", when acted upon by potassium, yields hydrate of potassium, or potassic water KHO". Hydrate of potassium acted upon by iodide of ethyl yields alcohol, or ethylated water EtHO". Alcohol acted upon by potassium yields potassiumalcohol, or ethylated potassic water EtKO". Potassium-alcohol acted on by iodide of methyl yields the first mixed ether, or methylated ethylwater EtMeO"; and when acted upon by iodide of ethyl yields common ether, or ethylated ethyl-water Et,O". None of the intermediate bodies can be represented save with 16 parts of oxygen, and hence the terminal bodies being members of the same series, must be also represented with 16 parts of oxygen. The intimate relations and analogies of ethylated methyl-water EtMeO" and diethylated water Et.O", as regards modes of formation, modes of decomposition, boiling point, vapour-density, &c., will not allow the molecule of the mixed ether to be represented with 16 parts, and that of the common ether with only 8 parts of oxygen; any more than the relations and analogies of ethyl-methyl-phenylamine EtMe PhN" and triethylamine Et.N" will allow the molecule of the former compound to be represented with 14 parts, and that of the latter with only 4-7 parts of nitrogen.

With regard to chlorhydric acid, there is no intermediate stage in the replacement of its hydrogen; the substitution taking place at once or not at all. We have, for instance, chloride of hydrogen HCl, chloride of ethyl EtCl, and chloride of sodium NaCl, but no intermediate

bodies; whence the representation of chlorhydric acid by the simple monhydric model, thus :

In addition to the above-mentioned chemical parallel, there is one very remarkable physical relation subsisting between marsh-gas, ammonia, water, and chlorhydric acid, namely, that all four molecules occupy the same bulk. Two cubic feet, for instance, of chlorhydric acid-gas HCl, yield 1 cubic foot of hydrogen and 1 cubic foot of chlorine. Two cubic feet of steam H,O, yield 2 cubic feet of hydrogen and 1 cubic foot of oxygen. Two cubic feet of ammonia H,N, yield 3 cubic feet of hydrogen and 1 cubic foot of nitrogen; while two cubic feet of marsh-gas HC, yield 4 cubic feet of hydrogen and a quantity of carbon of which the gaseous volume has not been and cannot be ascertained. With equal volumes of all four gases, the marsh-gas contains four times as much, the ammonia three times as much, and the steam twice as much hydrogen as the chlorhydric acid.

Many other arguments may be adduced to show that the molecular weight of water is 18, corresponding to the formula H,O", and not 9, corresponding to the formula HO'. Thus water is concerned as the agent or product of some chemical reaction more frequently than any other body with which chemists are acquainted; but in no well-defined reaction do we ever find the reacting or resulting water expressible by 9 parts, or three times 9 parts, or five times 9 parts, &c., but in every case by 18 parts, or some multiple of 18 parts, as instanced in the following examples, which might be increased indefinitely :

Formation of Nitro-benzol.

C.H. + HNO

2C.H

= CH,(NO2) + H2O" or 2 HO'

Decomposition of Zinc-ethyl.

+ ZnH2O, = Zn(C2H1), + 2H,O" or 4 HO'

Again, in the great majority of direct compounds which water forms with other bodies, the combining water necessarily constitutes 18 parts, or some multiple of 18 parts; and when two or more bodies differ from one another by the quantities of water they respectively contain, the differential quantity always amounts to 18 parts or some multiple of 18 parts, thus:

Several chemists, during what may be termed the transitional stage of their views, were accustomed to represent the molecule of water by the formula H2O'2, in which O' stands for 8 parts of oxygen, instead of by the formula H.O", in which O" stands for 16 parts by weight of oxygen. But the use of this formula really showed an imperfect appreciation of the grounds upon which the abandonment of the simpler formula HO' was based; for if the molecule of water is to be represented with two proportions of hydrogen, because its hydrogen is divisible into two parts, invertendo it must be represented with but one proportion of oxygen, because its oxygen is indivisible. Now that the oxygen of water is indivisible is acknowledged alike by those who use the formula H2O" and those who use, or rather used, the formula H.O',; and such being the case, the representation of the oxygen of water by the expression O', is quite unwarrantable, for the conception of two inseparable proportions of oxygen having each the value 8, amounts after all to that of a single indivisible proportion of oxygen having the value 16.

That the oxygen not only of water but of all other well-defined oxygenated molecules always amounts to 16 parts, or some multiple of 16 parts, is abundantly evident. For the composition alone of the great majority of oxygenated bodies, prevents them from being represented save with 16 or some multiple of 16 parts of oxygen, just as the composition of chloroform prevents its being represented save with 12 parts of carbon; and as the composition of ethylamine prevents its being represented save with 14 parts of nitrogen. With regard to the remaining oxygenated bodies, their mere composition would allow them to be represented with only 8 or some odd multiple of 8 parts of oxygen, but their several relations to other bodies belonging to the more numerous class prevents them from being represented with so

small a quantity; just as the relation of triethylamine to ethylamine and diethylamine prevents it from being represented with less than 14 parts of nitrogen, though from its mere composition it might be represented with only 4.7 parts of nitrogen.

From this it follows, that when two or more bodies differ in composition from one another by the proportions of oxygen they respectively contain, that difference always amounts to 16 parts, or some multiple of 16 parts, as shown in the following series:

Throughout there is no difference of 8 parts of oxygen or of any odd multiple of 8 parts of oxygen, between the successive compounds.

It follows also that whenever oxygen, with or without some other element, is added to or taken from a compound, the oxygen so added or eliminated must always be represented by 16, or some multiple of 16 parts, as instanced in the following decompositions, representing the liberation of oxygen from nitrate, permanganate, and chlorate of potassium respectively :

KCI

+0" or O',

2

2H SO. + KMMO, = 2H,O + KMm(SO.), + O", or O' + 0"3 or O'

KCIO, =

Let the decompositions be expressed how they may, the oxygen displaced cannot appear as 8 parts, or any odd multiple of 8 parts; and so in hundreds of other instances.

The representation of the molecule of water by the formula H,O was proposed by Gay-Lussac, advocated by Berzelius, and employed by Davy more than fifty years ago. Its revival is due to Gerhardt, who in conjunction with Laurent made it the basis of a consistent system of chemistry, since brought to a higher state of development by the labours of many distinguished chemists, including more especially

Professor Williamson, who first introduced it into this country and supported it by a series of most masterly researches.

In accordance with this system, four well-defined classes of primary hydrides are recognized, the leading member of each of which constitutes the type or model to which an infinite variety of compounds are referable as regards both their composition and behaviour; thus:

Formulated as above, all these hydrides occupy the same volume, and their respective vapour-densities compared with that of hydrogen as unity are the halves of their atomic weights.

[W. O.]

WEEKLY EVENING MEETING,

Friday, May 22, 1863.

The Rev. JOHN BARLOW, M.A. F.R.S. Vice-President, in the Chair.

PROFESSOR ROSCOE, B.A. F.C.S.

On the Direct Measurement of the Sun's Chemical Action.

THE life of the animal may be described chemically as a process of oxidation the tissues of his body are continually undergoing combustion; he is constantly breathing out carbonic acid gas, and thus deteriorating the ocean of air at the bottom of which he lives and moves; so that, were not a counteracting influence at work, he would, during each moment of his existence, be working his own destruction. This counteracting influence is exerted by vegetables, whose life is chemically characterised by a change opposite to that of the animal, that, namely, of deoxidation or reduction. Animals take up oxygen and give off carbonic acid; plants reverse the process, they take up carbonic acid and give off oxygen; and thus the balance of atmospheric life is kept always true.

The animal derives its power from the forces locked up in the