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Preliminary Report on the Thermal Equivalents of the Oxides of

Chlorine. By James DEWAR, F.R.S.E. During the course of the last Meeting of the British Association, I took occasion to lay before the Chemical Section two short notes bearing directly on the subject of Thermal Equivalents; they were respectively entitled “ Thermal Equivalents and Fermentation," and “ Observations on the Oxides of Chlorine.” In the first-mentioned communication it was proved that the decomposition of sugar into carbonic acid and alcohol was a reaction taking place without any great evolution of heat, if we accepted the thermal equivalent of sugar as determined by Frankland, along with the similar value of alcohol obtained from Favre and Silbermann's researches; and consequently the heat of fermentation must be derived from some other source than the sugar molecule itself,—the continued hydration of the alcohol produced, the secondary decompositions taking place, and the transformations of the ferment itself being the three available sources of supply

The note on the oxides of chlorine had special reference to the heat evolved during the decomposition of these oxides. The researches of Favre and Silbermann having shown that the formation of hypochlorous acid and of chloric acid is attended with a large absorption of heat, it became interesting to ascertain if in this series of oxides we had a regular increment of absorption in passing from the lowest member of the series to the highest member, just as Andrews had found a similar relation to hold for certain oxides of the same metal, whose successive formation was attended with an evolution of heat. I suggested it would be interesting to make a completo examination of the thermal relations of these bodies along with the similar derivatives of bromine and iodine, and with this object in view I accepted a grant in order to prosecute these researches; and although my spare time has been variously occupied during the past year, I have found opportunity to make a considerable number of preliminary observations in connexion with this subject. Heat absorbed during the Solution of Salts belonging to this Series per


Heat units.
KCI .............


KBr............ 4900 KBro,

9,680 KI ............ 4800


5,300 Comparing the solution-values of chloride of potassium and bromide of potassium with the corresponding values obtained for the chlorate and bromate, the latter salts are observed to have a very much higher solution thermal equivalent; whereas, comparing iodide of potassium with iodate, we have only a slight increase in the latter salt. The highest absorptionvalues are therefore connected with the acids whose formation is attended with an absorption of heat. It will be interesting to find how these substances act with regard to the absorption of radiant heat, and if a similar relation is maintained.

The method I proposed to adopt in examining the thermal relation of the oxides of chlorine was based on the easy and rapid decomposition of dilute hydriodic acid, whose thermal equivalent in aqueous solution has been carefully determined. I soon found, however, chloric acid did not appreciably decompose dilute hydriodic acid when the strength of the respective acids in aqueous solution amounted to a half gramme equivalent per litre, nor did I

succeed better when I substituted hydrochloric acid for the hydriodic. A few experiments were made on the action of magnesium on chloric acid, with the view of ascertaining its thermal value from the oxidation of the nascent hydrogen ; but, so far as my experiments extended, the results did not agree satisfactorily.

I had recourse then to the direct action of iodine on chloric acid, which I found acted easily on a solution of twice the normal strength, at a temperature of 80° C., although it did not act on a dilute aqueous solution in the cold. The reaction only taking place readily at a temperature of 80° C., complicates very much the mode of procedure, necessitating, as it does, a very constant temperature.

A series of observations gave as a mean 35,500 heat units evolved per equivalent of iodine acting on excess of chloric acid. This number represents the heat evolved in the transformation of chloric acid into iodic acid ; and by subtracting from it the thermal value of the latter acid, we obtain the heat evolved from the decomposition of the chloric acid. The thermal value of iodic acid is very readily obtained through the reaction of dilute hydriodic acid, thus

10,+5H1=5H0+61, which takes place with extreme rapidity in dilute solution, evolving 16,000 units per equivalent of hydriodic acid decomposed.

Assuming, then, the thermal value of hydrogen to be 34,000 units, and that of hydriodic acid to be 15,000, we obtain on calculation 15,000 units evolved during the formation of a molecule of iodic acid in aqueous solution. This number agrees very closely with that of A. Ditte's for the formation of iodic acid as found through the oxidation of phosphorus. Subtracting the number found for the formation of dilute iodic acid from the former number expressing the action of iodine on dilute chloric acid, we have the number 20,500 left for the thermal value of dilute chloric acid. Favre estimated the thermal value of dilute chloric acid as high as — 65,234 per equivalent this result being based on the action of chlorine on concentrated caustic potash, thus,


and inserting in the equation the known values of oxide of potassium and chloride of potassium, and further correcting for dilution. It is obvious, however, where we have one atom of a compound formed for five atoms of another whose thermal value is not very accurately known, we multiply any error enormously.

In looking over Favre's original paper, in the Journal de Pharmacie’ for 1853, on this subject, I observed that he mentioned a very curious observation with reference to the heat evolved during the saturation of hypochlorous acid with dilute oxide of potassium. He shows that an equivalent of caustic potash, when neutralized with an equivalent of hypochlorous, gives rise to an evolution of 10,768 heat units ;. but if two molecules of hypochlorous acid were employed per equivalent of caustic potash, he found an evolution of 22,114 heat units. The additional heat evolved is not due to the formation of an acid salt, because, on adding another atom of caustic potash, we obtain the normal amount of heat due to the saturation of the acid. It is reasonable to suppose, therefore, that the additional atom of hypochlorous acid induces the following reaction :


a decomposition that is well known to occur in certain conditions. As-
suming this equation to be correct, and employing the following thermal
numbers admitted by Favre-
Formation of KO

76,238 per equivalent.
KO with Cho = 10,678

KO with clon = 15,187
Cl with O

=- 7,370 KO CIO condensing= 11,436 we obtain for the formation of an equivalent of aqueous chloric acid

- 12,661 heat units. This number is only about one-fifth part of the former number admitted by Favre.

There is yet another mode of arriving at the thermal value of chloric acid. Frankland recently made a series of observations on the heat evolved during the oxidation of many organic substances through the action of chlorate of potash, and had necessarily to deduce from the total heat evolved the heat due to the decomposition of the chlorate of potash employed; his highest result amounts to 5500 heat units evolved per equivalent of chlorate of potash decomposed. Now it is easy, from the admitted decomposition and with the aid of this result, to calculate the thermal value of chloric acid.

KO C10;=KCI+06
Formation of KCI



= 76,238 KO with CIO, = 15,187 KO CIO, solution = 10,100



The various determinations of the thermal value of chloric acid are inserted in the following Table, along with a reference to the reaction on which the determination is based :

Action of chlorine on concentrated caustic potash =-65,234 (Favre).
Condensation of hypochlorous acid

=-12,661 (Favre). Decomposition of chlorate of potash

=- 6,000 (Frankland). Action of iodine on chloric acid

=-20,500 (Dewar).

The great difference in these results shows that even with the greatest care experimenters are apt to differ on the intricate subject of thermal values, and that before a satisfactory conclusion can be arrived at with reference to the true thermal value of chloric acid further experiments ought to be made.

A series of observations have been made on chlorous acid and on the peroxide of chlorine.

Chlorous acid was obtained by the action of benzol sulphuric acid on chlorate of potash, and after washing it was passed directly into water, in order to obtain a dilute solution.

The analysis of the solution has invariably differed from that of a solution of pure chlorous acid ; and it seems absolutely necessary, in order to ensure the purity of the aqueous solution, that the acid be previously liquefied, and its vapour passed slowly into water, as has been recommended by Brandeau. As the cold weather had all vanished before I could secure time to enter on this investigation, I saw it was hopeless to prepare the liquid acid readily and thus ensure a pure product, but made a few observations on the purest product I could obtain—the highest number I have obtained per equivalent of chlorous acid, C10,, acting on hydriodic acid amounting to 111,000 units, the following reaction taking place, thus,

C10, +4HI=HC1+3H0+I.. It is easy to calculate the heat absorbed during the formation of dilute chlorous acid, and it is found to amount to - 27,800 heat units.

Similar observations have been made on peroxide of chlorine obtained from the action of oxalic acid on chlorate of potash. The aqueous solution of the gas has always contained appreciable quantities of free chlorine, and the value obtained will necessarily require some correction. One equivalent of Clo, acting on hydriodic acid evolves 120,000 heat units; the following reaction takes place :

010, +5HI=HC1+4H0+Is. When the requisite numbers are inserted in the above equation, the result is found to be 19,800 heat units absorbed for the formation of an equivalent of peroxide of chlorine.

The thermal values of chlorous acid and of peroxide of chlorine are likely to require considerable correction, because I have not found that strict uniformity in the results I should have liked. This is owing in great part to the difficulty of procuring a pure product, and the great tendency to secondary decomposition. The mode of conducting the experiments may also have considerable influence on the results. The above experiments were made with the relative proportions of the oxides of chlorine and of hydriodic acid that would completely neutralize each other, so as to precipitate the iodine in the free state. A series of experiments made in presence of excess of hydriodic acid, the requisite correction being made for the solution of the iodine, would be important, and these I intend to execute along with further observations on this subject.

The following observations have been made in connexion with this report:Action of dilute HCl on dilute HC10g....... ..... nothing


nothing HO.

- 730


.............. noming

HIO, (per eq. of HI).... 16,000
HI (per eq. of C10,) ....111,000
HI (per eq. of C10) ....120,000





IO, .....


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Report on the practicability of establishing A Close Time" for the

protection of indigenous Animals. By a Committee, consisting of Prof. NEWTON, M.A., F.R.S., Rev. H. B. TRISTRAM, F.R.S., J. E. HARTING, F.L.S., F.Z.S., Rev. H. BARNES, and H. E. DRESSER

(Reporter). Your Committee has great pleasure in reporting that the object for which it was appointed has continued to excite attention in the public prints during the past year, and that in the direction indicated by its last Report—the protection, namely, of those birds generally coming under the term “ Wild Fowl.” There appears to be a widespread disposition among all classes to extend in their favour the provisions of the Sea-Birds’ Preservation Act,' in proof of which your Committee may cite two facts :—1, the establishment in the county of Sussex (chiefly through the instrumentality of Mr. T. J. Monk, of Lewes) of an Association whose members pledge themselves to abstain from destroying Woodcocks in the breeding-season, which Association has met with great encouragement from the principal landed proprietors in the county; and 2, the rapid growth of a well-founded belief that some steps are absolutely necessary to stop the netting or shooting of Plovers during the same season to ensure a continuance of the supply of their eggs, which form, as is well known, a valuable commodity.

Your Committee is fully aware of the danger of attempting to legislate on this subject before the proper time; but from the assistance which has been promised in various influential quarters, it entertains a sanguine hope that some decided step may be taken next year; and believing that the warmest supporters of the principle of establishing a Close Time for indigenous animals will readily listen to the recommendations of your Committee, it respectfully prays that your Committee may be reappointed.

Report of the Committee on Earthquakes in Scotland. The Committee

consists of Dr. BRYCE, F.G.S., Sir W. Thomson, F.R.S., D. MILNE

HOME, F.R.S.E., P. MACFARLANE, and J. BROUGH. VERY little worthy of record has occurred during the past year. There has been no earthquake or other disturbance in the Comrie district similar to those noticed in last Report. From other districts, however, slight shocks of earthquake have been reported—from Lochaber in the end of November and from the upper part of the Frith of Clyde in April. The latter occurred during the night, was noticed by few, and doubt has been expressed by some in regard to it. But as the same region was certainly agitated on more than one occasion during the conduct of the previous inquiry instituted by the Association, of which Dr. Buckland and Mr. Milne-Home had the charge, there is no improbability in such an occurrence; very little information, however, that could be depended upon was obtained. In regard to the other earthquake-shock there is less doubt. The district in which it was felt comprises the Spean Valley and the lower part of the Great Glen, a region in which some of the most severe of our earthquakes have been from time to time experienced. In the present case, however, no change was produced on the surface, or in the position of objects (see Rep. by Mr. D. Milne-Home, Brit. Assoc. Rep. 1840); and without recording instruments

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