and another atom of ethyl can be substituted for it, and the resulting body is ethylate of ethyl. The well-known gas, marsh gas, CH, is the hydride of methyl, and is, therefore, referable

CH3
H'

to this type; its preparation from sodic acetate and sodic hydrate confirms this, for, although the action is in one sense analytical, it is, as regards the formation of marsh gas, truly synthetical

Na (C, H, O2) + Na HO = C H, H + Na, CO,

3

(Marsh gas).

for methyl, C H,, is afforded by the sodic acetate, and hydrogen by the sodic hydrate.

When the elements of a molecule of water are expelled by heat from a molecule of acetate of ammonium, a body remains, the composition of which may be explained by writing it on the type of a molecule of ammonia.

This body is termed acetamide, and is one of a large class of ammonias in which acid radicals are substituted for the atoms of hydrogen in ammonia. These amides, as well as the amines (whose constitution differs from them in this respect, that, whereas the amides contain hydrogen, the amines do not), may all be represented on the ammonia type. The well-known compound, urea, which is an amide of carbonic oxide, will serve as a good illustration, and it is ammonia in which two atoms of hydrogen have been replaced by CO, the substitution is easily understood, when ammonia is made to act on ethylic carbonate. It may be well, in order to simplify the matter, to show first the formation of ethylic carbonate. Carbonic acid, plus the elements of a molecule of water, may be represented thus: on the type of two molecules of water, and if two atoms of ethyl be substituted for the two atoms of

CO

H2

} 0.

2

CO

typical hydrogen, we shall get (C, H ̧).

O, ethylic carbonate, and

2

when this is acted upon by ammonia, we shall get the following decomposition

it is here clearly seen that CO is directly made to take the place of

two atoms of hydrogen in two molecules of ammonia. Another reaction, by which urea is produced, also confirms this synthesis; cyanate of potassium, with sulphate of ammonium, gives the following double decomposition

The ammonia type is also used to represent the constitution of those compounds which other trivalent elements form with hydrogen; and in which it may be considered that the nitrogen in ammonia is replaced by phosphorous, arsenic, or antimony.

Phosphoretted hydrogen PH, is evidently an ammonia in which the nitrogen is replaced by phosphorus, and may be written on that type, as also may be arsenuretted and antimonuretted hydrogen.

We have hitherto only considered those cases in which the hydrogen of the type is replaced by elements or radicals. The chlorous element can also be changed, and this is well illustrated in the case of sulphuretted hydrogen, which, from its formation, may be regarded as a molecule of water in which the atom of oxygen is replaced by an atom of sulphur; for if hydrogen be evolved from water in the presence of hydro-sulphurous acid, sulphuretted hydrogen is given off; and this can be effected by mixing hyposulphite of soda with water and sodium amalgam, the hydrogen evolved from the water by the action of the sodium decomposes the hyposulphite, sulphur being set free, which at the moment of its liberation unites with hydrogen, taking the place of the oxygen of the water which has been abstracted by the sodium to form sodic oxide Na O. In addition to the simple types, which have been briefly noticed, others are employed, without which it would be possible to represent only a very limited number of reactions; for example, phosphoric acid (tribasic H, PO,) may be represented on the type of three molecules of water or on that of two

PO

H,

39

molecules of water POO,, in which the first radical PO can

H3

2

2

replace three atoms of hydrogen, but the second PO, is able to replace but one. Meta-phosphoric acid may be represented on the type of one or two molecules of water thus:

РО

H

} O.. It is, however, beyond our present purpose to go more

fully into this very interesting subject. For further information on the "Constitution of Acids and Salts," the reader is referred to a remarkably clear and able paper, by Professor Odling, in the journal of the Chemical Society.*

Before dismissing this subject, however, there is another kind of type which should be noticed, as it makes clear the constitution of such bodies as the hypo-sulphites; it is a compound type, and its application is peculiarly useful where the types we have been considering do not appear to be sufficiently comprehensive. Hyposulphite of soda, a salt of considerable importance, is made by passing sulphurous acid SO, into a solution of sodic sulphide, and the formula of the salt is Na,S,O,. Rose says that there is also a molecule of water (constituent water) in this salt, and that the formula for it is Na, H,S,O,. Whether this be the case or not, it does not seem to make any difference in the formation of the salt, which is effected by the replacement of two atoms of hydrogen in one molecule of water, and one of sulphuretted hydrogen by sulphurous acid SO, thus

2

so that one atom of hydrogen is taken from the water, and another from the sulphuretted hydrogen, their place being supplied by the radical SO,, which binds them together into a new compoundhypo-sulphurous acid.

I had intended entering somewhat fully into the consideration of what is termed the saturation of molecules; the subject has been already alluded to several times; it is, however, one whose range is so wide, that it seems better to leave it for a separate treatment, which it well deserves, at some future time. The attention of chemists has been of late much directed to it, and various methods

"Chem. Soc. Journ.," vol. vii., page 1.

2

have been recommended for rendering clear and intelligible what is, to say the least of it, a very difficult subject. Graphic formulas have been devised and material representations of atoms used, which, however much they may assist in explanation, tend to give incorrect views, as representing what we have had, as yet, no opportunity of knowing, viz., the form and arrangement of atoms in a molecule. It is sufficient for the present to state that, with few exceptions, the free molecule has all the valent powers of its constituent atoms satisfied; by this is meant that, in such a body as marsh gas, CH,, carbon, which is tetravalent, is completely satisfied by the four atoms of hydrogen which enter into its composition; and that, in olefiant gas, C, H,, the carbon is only half satisfied by four atoms of hydrogen, for the carbon is double what it is in marsh gas, and the remaining carbon of one atom satisfies the remaining carbon of the other; that is, the carbon which is not satisfied by hydrogen; and the molecule is stable, its atoms being all held firmly together by the powerful attraction which the carbon has for itself. A good illustration of the force with which the atoms of an element unite with one another is afforded by the decomposition of iodide of nitrogen. Here we have an unstable body which is decomposed even by the friction of a feather on its surface, and the decomposition is attended by the evolution of light and intense heat, a violent explosion accompanying the action. But decomposition is always attended by the absorption of heat, how then is this apparently strange manifestation to be accounted for? The atoms of iodine and nitrogen, when set free from their forced union, unite together to form molecules of the free elements, and as has been shown before, in the case of iodide and iodate of potassium, a very slight disturbing force destroys an equilibrium which is, at the best, but unstable; and the heat and light evolved in the decomposition of iodide of nitrogen are consequent on the union of some atoms of nitrogen with others, to form free nitrogen, and those of iodine with iodine to form the free element. Again, in water, oxygen holds together two atoms of hydrogen by its divalent property. In

acetate of potash, CHOO, where one atom of hydrogen in the

3

K

molecule of water has been replaced by othyl and the other by potassium, oxygen exerts the force which holds the atoms of the molecule of that salt together; and the power of oxygen is great, for, when two atoms of chlorine are substituted for oxygen, by the action of pentachloride of phosphorus, they have not the power to preserve the molecule entire; it breaks up into two separate com

C2H2O.

2

3

pounds, hydrochloric acid, HCl, and chloride of othyl, Cl From these examples it will be seen, that in compounds there is an element which acts as a coupler, so to speak, which collects around it and holds firmly together other bodies, elements, or compounds, with which it is for the time associated, and it continues to hold them, until it is itself overpowered by the action of some reagent whose influence it cannot resist, and that the stability of a compound depends upon the force which this element or radical is able to exert. From the brief and imperfect explanation of some of the new theories in chemistry, which has been given in these articles, it is to be hoped that the reader, who was before unacquainted with them, will be led to see that, however imperfect our present knowledge and theories may be, still vast strides have been made, based on a sound and rational foundation, in a direction which is continually leading to the discovery of fresh facts, confirmatory of those views which we have been considering, and for a knowledge of which the writer is mainly indebted to the teachings of Professor Williamson.

VEGETABLE FIBRES AND THEIR MICROSCOPIC

CHARACTERS.

BY M. VETILLARD.*

LINEN, FLAX.-When we examine with the naked eye a filament of the finest and best flax, we are tempted to suppose it simple and homogeneous. On submitting it to the microscope we find that it is a bundle of slender fibres in juxtaposition and adhering one to another. If we destroy this adhesion by the successive and moderate application of boiling alkalies and alkaline chlorides, and by the mechanical action of a couple of needles under the simple microscope, we at last obtain separate fibres, varying in length from several millimetres to 0.06m, and less. If we place these fibres in an asphalt cell with glycerine or, still better, with one of the liquids employed by M. Bourgogne, and magnify them two hundred or three hundred times, the following characters appear.

The isolated fibres, or cells composing the flax filaments are seen as transparent tubes, the internal cavity of which is very small as compared with the external diameter. Frequently this cavity is not * Translated from "Comptes Rendus." No. 19. 1868.