ARGUMENTS FOR DOUBLING THE ATOMIC WEIGHT OF OXYGEN. 49

In all cases, intermediate oxides and sulphides, such as those shown at 2, 4, 5, 7, 8, and 9, may be traced, whilst in no case can any intermediate chlorides or bromides be formed: in other words, two different radicles may be united into one compound when oxygen or sulphur is combined with them; whilst this is never the case with chlorine or with bromine. Hence it is argued, that the quantities of oxygen and of sulphur indicated by → and S in the foregoing formulæ are not really two atoms, as was formerly supposed, but rather that they represent an indivisible whole, or, in fact, one atom. In consequence of this, two

atoms of each of the other elements or radicles are united with → or S, and are held together as one group, owing to the indivisibility of the quantities of the elements represented by the symbols → and S. On the other hand, the non-existence of such intermediate compounds, or compounds containing two different elements or radicles, amongst the chlorides and the bromides, is an indication that no such cause of union exists in the atomic constitution of chlorine and of bromine; but that the quantities represented respectively by the symbols Cl and Br correspond truly to the atoms of these bodies.

The different metamorphoses which many bodies undergo

50 ARGUMENTS FOR DOUBLING THE ATOMIC WEIGHT OF OXYGEN.

under the influence, on the one hand, of certain sulphuretted, and on the other of certain chlorinated compounds, have been further adduced in support of this view.

When, for instance, alcohol or acetic acid is acted upon by a sulphuretted body such as pentasulphide of phosphorus, a single new sulphuretted body is formed; but when the same compounds are acted upon by a body which furnishes chlorine, such as pentachloride of phosphorus, two new chlorinated derivatives are produced; for example:

(¤‚H¿)H‚Ð+PC1;= [(Є,H ̧) Cl and HCI] + PCI ̧Ð ;

Acetic acid.

5

Acetyl chloride.

(¤ ̧H ̧‡) H‚Ð+PCl ̧=[(€‚H,→) Cl and HC1] + PC1 ̧Ð.

The groups ЄH, and H, on the one hand, and the groups Є2H ̧Ð and H on the other, are held together by the indivisible quantity

or ; whilst they separate into two distinct bodies as soon as chlorine takes the place of the oxygen, because the quantity of chlorine (Cl) which displaces the quantity of oxygen () is really not a single atom, but two atoms.

Analogous reasoning may be extended to the case of the compounds of carbon, the ordinary atomic weight of which has also been doubled on similar grounds.

Selenium and tellurium, from their analogy with sulphur, are also indicated with double atomic weights; and we have already, on other grounds, shown the advantage of doubling that of silicon and of certain of the metals. These new atomic weights may be distinguished from those still employed by many chemists by the use of italics, or still better, of barred letters. We have, in the last volume, pointed out that if it be desired to translate formulæ written with the new symbols into those formerly made use of, it is simply necessary to multiply the numbers of the atoms of oxygen, sulphur, carbon, and the other elements indicated with

barred symbols by 2, whilst the plain letters remain unaltered; for instance:

(1063) Chemical Types.-The homologous series of the alcohols which has already been briefly reviewed (1059) has its representatives among the simpler compounds contained in the department of inorganic chemistry; for by deducting 2 (EH) from the formula of the molecule of methyl and the compounds of the methylic group (contained in the horizontal line 1 in the Table, p. 40), we arrive at hydrogen and some of its most important compounds of simple constitution. For example, the molecule of methyl, if deprived of 2 (EH) would leave a residue consisting only of hydrogen; (ЄH2)2 2(CH)=H,. The molecule of methylic ether deprived of 2 (EH) would leave water; (ЄH,), 2 (ЄH2)=H2O: the residue from each molecule of methyl sulphide and of methylic mercaptan would be sulphuretted hydrogen. Methyl chloride after a deduction of EH, would become hydrochloric acid. Hence it appears that the radicles methyl, ethyl, trityl, tetryl, amyl, &c., are bodies which correspond to hydrogen, and that they may be regarded as homologues of a series in which hydrogen forms the lowest term; that the simple ethers and alcohols are homologues of water, whilst the chlorides and iodides are homologues of hydrochloric and hydriodic acid, and the sulphides and mercaptans are homologues of hydrosulphuric acid. Water, hydrochloric, and hydrosulphuric acid may, therefore, be regarded as the patterns or types upon which these several bodies are formed.

This idea of referring organic compounds to some simple representative or type was systematically worked out by Laurent and by Gerhardt.

The four principal types to which most of the compounds of organic chemistry are referred are the following:

1. The metallic or hydrogen type

H'

H'

or H2;

4. The marsh gas type

It is important to remark, that many bodies are referred to the same type, though they present no analogy in chemical properties, either to it or to each other. The various radicles which have been proved or assumed to exist in organic compounds vary in character as much as the elementary bodies themselves. Some, like cyanogen (EN), being strongly electro-negative, may be arranged with chlorine, oxygen, and sulphur, on the right-hand side of a double converging series; such as the following:

whilst others, like aldehyd and acetone, agree with arsenicum and antimony in occupying a central or intermediate position; and others, like kakodyl (Є,H,As) and the metallic derivatives of alcohol, would be arranged with the electro-positive bodies, potassium, sodium, calcium, &c., on the left-hand side of such a series. When we compare together different compounds belonging to the same series, a progressive change in properties is observed, so that the differences observable between any two such compounds become greater, the wider is the interval between the respective places in the series of the two terms submitted to the comparison. Following this idea to its extreme limits, the same type may therefore comprehend bodies belonging to the three classes of acids, of bases, and of neutral bodies; the acids or electro-negative bodies being at one extremity of the series, and the neutral bodies occupying the intermediate positions, provided that the bases or electro-positive bodies be arranged at the opposite extremity.

These types are to be regarded as types of double decomposition ; and are chiefly useful as representing the fact that the bodies which are referred to them experience a similar mode of decomposition when subjected to the action of the same chemical reagents.

The application of these types to the compounds of organic chemistry will be best understood by means of a few examples :(H'

1. The hydrogen or metallic type H

To this class may be referred the monad metals, as well as the

dyad metals, such as zinc and cadmium, of which the molecule consists of a single atom; and amongst organic compounds, the radicles of the monatomic alcohols, the hypothetical oxidized radicles of the monatomic acids, certain bodies formed by the union of two different monatomic radicles, such as the aldehyds and the ketones, as well as the dyad organic radicles of which the molecule consists of a single compound atom, such as ethylene-e.g.

Hydrochloric acid was originally proposed by Gerhardt as an

additional typical body, but the hydrochloric acid type zi

Cl

is now

usually included under the hydrogen type. It forms a subtype which comprehends the chlorides, fluorides, bromides, iodides, and cyanides of any monad radicle, including, therefore, the ethers of the hydracids, and the chlorides of the radicles of the monobasic acids; for example: