The members of this homologous series are all acted on in like manner by hydrochloric acid, yielding

All members of a homologous series can be expressed by a single general formula-that for the above alcohols, e.g., is CH2n+2O, or CH2n+1.OH.

As the products of the same reaction also form a homologous series, the reaction may be represented by a general equation. The conversion of the alcohols into the corresponding series of chlorides is given by the single general equation:

CnH2n+1.OH+HCl=CH2n+1C1+H2O.

49. The homology of organic bodies may be more or less complete ; it is the more complete the larger the number of homologous products that can be obtained from them, and the more energetic the reactions producing such products. For example, methylic alcohol,

CH,

он

CH3

, is as completely homologous as possible to ethylic alcohol, CH2,

он

or CH3.CH.OH. Of the two propylic alcohols, on the other hand, one is so in less degree than the other; but both are acted upon in the above-mentioned way by the halogen acids :

CH3.OH + HCl = CH3C1 + OH2

CH.CH.OH + HCl = CH3.CH2.Cl + OH2.

1. CH.CH.CH2.OH + HCl = CH3.CH2.CH2.Cl + OH2. 2. CH.CH(OH)CH3 + HCl = CH3.CHCI.CH3 + OH,. Towards oxygen, however, their behaviour is essentially different. By the action of one atom of oxygen they all yield oxides of the general formula CH2O; but that from the first propylic alcohol only is really homologous to those from both the lower homologues : CH3.OH+0= CH2.0 + OH, CH..CH.OH + 0 = CH..CHO + OH, CHÍCH,CH,OH + O = CH.CH,CHO + OH,,

2n

as these are all converted into homologous organic acids according to the general equation:

CnH2O+0= CnH2n+10.OH.

2n

The oxidation product from the second propylic alcohol, CH3.CO.CH3, though containing CH, more than CH3.CHO, still cannot unite simply with more oxygen, but on further oxidation takes up several oxygen atoms, with breaking up of the carbon nucleus.

PHYSICAL PROPERTIES OF ORGANIC BODIES.

Molecular and Atomic Volume.

50. The densities of organic bodies are the relative weights of equal volumes, at equal temperatures, expressed in abstract numbers; their specific gravities the weight of the volume unit of a cubic centimètre in grams. If the gram molecular weight of a body be divided by the specific gravity at a given temperature, the specific volume for that temperature-i.e. the volume in cubic centimètres of the molecular weight expressed in grams-is obtained. If the specific volumes be divested of their concrete significance, and conceived as abstract numbers only, they then form the relative molecular volumes. For example, the specific gravity at 0° of acetic acid is 1-075, its molecular weight = 60. Sixty grams of acetic acid at that temperature would therefore occupy a volume of 55.8 c.c.; this, then, is its specific volume. The specific volume of ethylic alcohol at 0° is similarly obtained as 57.05. Therefore the true molecules of acetic acid and of ethylic alcohol occupy at 0° spaces which are in the ratio of 55.8 57.1, these numbers forming the relative molecular volumes of the bodies.

51. Gases and vapours in the gaseous state contain, under like conditions of temperature and pressure, the same number of molecules in the same volume. Their specific and molecular volumes are, under the above conditions, equal to one another, whilst the specific gravities are directly as the molecular weights.

52. As fluids and solids do not expand equally for equal increments of temperature, they are not under like conditions of heat at equal temperatures; their specific and molecular volumes at like temperatures show no simple relation to one another. The molecular volumes of liquids near their boiling points, and of solids at their fusing points, show relations reducible to laws. These have been studied with more exactness in the case of liquids. If the molecular volumes of homologous compounds at their respective boiling points be compared with one another, there is found a difference proportional to that in the molecular weights, the molecular volume altering by about 22 for each alteration of the composition by CH2:

In bodies which contain an equal number of atoms of oxygen, but differ in their composition by (-C + H2),, the molecular volumes are equal:

The increase in the molecular volume by the addition of two hydrogen atoms is therefore as great as the diminution produced by the removal of one carbon atom, or the change in molecular volume by an atom of carbon is twice as great as that produced by an atom of hydrogen. As the group CH, in homologous compounds alters the molecular volume by 22, the C and H2 must have equal parts thereof i.e. the alteration caused by a carbon atom 11, by each hydrogen atom "/2=55. These alteration values of the single elementary atoms are termed their atomic volumes.

Atomic volume C = 11.

Atomic volume H= 5.5.

The atomic volumes of other elements can be calculated in a similar

manner.

An alcohol on conversion into an acid loses two hydrogen atoms, which are replaced by one oxygen atom, united by both its bonds to the same carbon atom. The alteration produced in molecular volume is very small, the mean result being + 1.2; e.g.

This gives as the molecular volume мy' of a compound resulting from the replacement of 2H by O, from the change of the ingredients, = MV' −11 + 12·2.

The atomic volume, therefore, of oxygen when united to carbon by both its bonds = 12.2.

The molecular volume is not altered to the same amount by an oxygen atom, which is united by one of its bonds only to a carbon atom. From a variety of determinations the atomic volume of oxygen, when united in this way, is found to be about 6.4.

By analogous methods the following atomic volumes have been

ascertained:

three bonds

=28.0

From these numbers the molecular volume of any organic compound can be calculated if the method of union of any oxygen, sulphur, or nitrogen atoms be known; e.g.

C1H,

со

он Valeric acid.

CH,

Molecular Volume. Calculated. Found.

= 5 x 11 + 10 × 5·5 + 12·2 + 6·4 = 128.6 130-2

These results can also be applied in determining the method of union of the oxygen, sulphur, and nitrogen atoms in organic compounds.

If in the case of aldehyde, C2H40, for instance, it were necessary to ascertain whether the formula should be written C2H3.OH or CH3

From the specific gravity of the body near its boiling point (21° C.) the molecular volume is found to be 56.45, showing the second formula to be correct.

It must be remarked, however, that the numbers calculated in the above way in many cases do not agree in a satisfactory manner with the molecular volumes derived from the found specific gravity. The values of the atomic volumes are still in part encumbered with considerable errors, and this must especially be the case with the atomic volume of carbon.

Just as an oxygen atom has a different atomic volume, when united by both bonds to the same atom, to that which it has when united by one bond only, so carbon may have different values according to whether it is united to another carbon atom by one, two, or three bonds.

The results of which the above is a summary were obtained at a time when the idea of a difference of the method of union of O, S, and N had already been partly evolved, but before any idea had been formed of the method of union of the carbon atoms. It is scarcely to be doubted that although a number of important points have been determined, still a repetition of the investigations, based on more complete recent theoretical views, would lead to very important modifications in our notions of atomic volumes.

The investigations of the molecular volume of solid organic bodies at analogous temperatures are not yet sufficiently complete to enable any laws to be deduced from them.

Melting Points and Boiling Points of Organic Bodies.

53. As melting and boiling points are amongst the characteristic properties of chemical bodies, they must be affected by the nature, number, and method of union of the elementary atoms forming the molecule. In what way these factors react upon the temperatures of fusion and ebullition is, however, not yet known, so that it is not possible to predict à priori these temperatures. Comparative investigations have, however, at least shown a few general laws, of which the following are the most important:

54. Melting Point. In homologous series the melting point frequently-but by no means invariably-increases with the molecular weight of the compound, without, however, these changes showing any complete parallelism with one another; e.g.

In many cases the group CH, exerts an influence in raising the melting point even where the CH, is united to the carbon nucleus by means of other elements, showing itself in opposition to the rule before mentioned of increase of molecular weight raising the melting point:

Similarly this influence is also perceived when the number of