The curves (Fig. 5) exhibit the values of p. It should be remembered that the author is only directly responsible for the changes in p, and that the absolute values are affected by errors, if any, in the "constant assumed" which is dependent on the accuracy of existing density determinations.

The values of are given partly in the hope that they will prove of practical value in physico-chemical work. In many branches of physical chemistry, solutions are prepared by dilution of stock solutions, and the experimenter wishes to know the concentration of the solution obtained, in, say, gram molecules per 100 grams of water. A continuous table of molecular volumes affords the easiest method of arriving at the result. Partly, again, because the values of X only tell us the volume change on 50 per cent. dilution, whereas the tables of gives us continuous information of the change of volume due to any given dilution. In the diagram, Fig. 5, is shown as a function of n for various substances. As, however, it would be impossible to depict the various curves on the same page without greatly diminishing the scale, it has been necessary to subtract a constant round number from the values of before plotting. These numbers are, for LiCl, 18; NaCl, 16; KCl, 27; HCl, 18; CaCl2, 10; SrCl, 11; Cane sugar, 209.

Conclusion.

The following empirical laws have been arrived at by the experiments described.

1. X (as defined on p. 268, Table IX) is in almost all cases given by the following equation, X= n/a, and, consequently, & (as defined, p. 273) must be given by

2. For comparable substances and concentrations, X increases with the equivalent weight of the substance in a regular way.

It is hoped that these empirical rules, together with the tables of contraction and of molecular volumes, will be sufficient excuse for the publication of this paper. It should be added that the apparatus described is applicable without modification to many other physicochemical problems, such as change of volume on neutralisation, change of volume on mixing two different liquids (for example, alcohol and water), changes of volume on formation of double salts in solution. The author hopes to proceed with the study of volume changes on neutralisation of organic acids without delay.

The writer's best thanks are due to Prof. J. J. Thomson for permission to work in the Cavendish Laboratory, and to Mr. Griffiths and Mr. Whetham for the interest taken in the work throughout.

XXIX.-Methanetrisulphonic Acid.

By ERNEST HAROLD BAGNALL, B.Sc.

THE sulphonic acids of methane, the simplest hydrocarbon, are substances of more than ordinary interest, and, although the mono-, di-, and tri-sulphonic acids, CH, HSO3, CH2(HSO3)2, and CH(HSO3)3, have long been known, no work on them has been published during the last five-and-twenty or thirty years.

Of these, methanetrisulphonic acid, CH(HSO), the subject of this paper, was discovered by Theilkuhl (Annalen, 1868, 147, 134), and subsequently examined by Rathke (ibid., 1873, 167, 219).

In attempting to prepare the various sulphonic acids and sulphones of dichlorobenzidine by the action of fuming sulphuric acid on dichlorodiacetylbenzidine, a substance was obtained which, on analysis, was found to be methanetrisulphonic acid; as it can be easily prepared by the methods described in this paper, I have carefully examined the acid, and also studied the properties of its various salts.

Preliminary experiments soon showed that the formation of methanetrisulphonic acid was really due to the presence of the acetyl groups in dichlorodiacetylbenzidine, as diacetylbenzidine under similar treatment gave a large quantity of the acid, whereas benzidine sulphate gave only benzidinesulphone and the various sulphonic acids of benzidine (Ber., 21, Ref., 873; 22, 2467). Similarly, acetyl-a-naphthylamine gave a small quantity of methanetrisulphonic acid.

As this reaction appeared to be a general one for the acetyl derivatives of benzidine and naphthylamine, it was anticipated that the acetyl derivative of aniline and the anilides of the higher fatty acids would yield methanetrisulphonic acid, or its homologues, as one of the products, and this was found to be so in the case of acetanilide. Acetanilide, when heated with fuming sulphuric acid, gives a remarkably good yield of methanetrisulphonic acid, along with anilinedisulphonic acid, NH, CH(HSO3)2 [1:2:4]. Other anilides were experimented with, but the results were not satisfactory; the anilide of propionic acid gave a very small quantity of methanetrisulphonic acid, but neither ethanedisulphonic acid nor sulphopropionic acid could be detected (compare Buckton and Hofmann, J. Chem. Soc., 1856, 9, p. 241).

2

It is difficult to understand the general nature of these reactions. Much sulphurous anhydride and carbonic anhydride are always evolved, and it seems probable that some of the organic substance is oxidised to carbonic anhydride, and some converted into aromatic sulphonic acids,

the acetyl group alone reacting with the fuming sulphuric acid to form methanetrisulphonic acid. Glacial acetic acid, however, when heated with fuming sulphuric acid, gives no methanetrisulphonic acid; the sulphur trioxide dissolves in the acetic acid without giving off gas, and sulphacetic acid, CH,(HSO) COOH, is formed. It was anticipated that, on heating acetamide with a large excess of fuming sulphuric acid, methanetrisulphonic acid would also be produced, but this is not the case; the product consists entirely of methanedisulphonic acid, CH2(HSO3)2, which was first isolated by Liebig (Annalen, 1835, 13, 35), and subsequently prepared and examined by Wetherill (ibid., 1850, 66, 122), Strecker (ibid., 1856, 100, 199), and by Buckton and Hofmann (J. Chem. Soc., 1856, 9, 241), and Rathke (Annalen, 1873, 161, 152).

EXPERIMENTAL.

Preparation of Methanetrisulphonic Acid.

Action of Fuming Sulphuric Acid on Dichlorodiacetylbenzidine.— As stated in the introduction, it was from this substance I first obtained methanetrisulphonic acid. Dry powdered dichlorodiacetylbenzidine (16.85 grams) was heated on a water-bath at 100° with fuming sulphuric acid (100 grams, containing 70 per cent. free SO), mixed with pure sulphuric acid (100 grams) until the whole dissolved.* The mixture was then heated for 3 hours on a sand-bath at a temperature of 150°, with constant stirring, and left overnight. It was then poured on to ice, filtered to remove a dirty green precipitate which probably contains the sulphones and sulphonic acids of dichlorobenzidine, and the dark brown filtrate neutralised with milk of lime, heated to boiling, and rapidly filtered from the precipitated calcium sulphate. To the clear filtrate, evaporated to a small bulk, sodium carbonate solution was added in quantity just sufficient to precipitate all the calcium as carbonate. This was filtered off, and the filtrate concentrated and allowed to cool slowly, when it deposited yellow crystals; these were collected, dissolved in a small quantity of water, and glacial acetic acid added; the white, crystalline precipitate of the sodium salt of methanetrisulphonic acid, CH(NaSO3)3+3H2O, thus obtained, was analysed.

Great care is required in the mixing of fuming sulphuric acid with concentrated sulphuric acid; to prevent accident, the concentrated sulphuric acid should be poured into the fuming acid, not vice versa.

It is better to carry out these sulphonations in a porcelain beaker, the mouth of which is covered with a close-fitting clock-glass. A hole is bored through the centre of the clock-glass, so as to admit a glass stirring rod which is connected with a water-motor. With this arrangement, very little sulphuric anhydride escapes into the air.