phosphate was added to the magnesium salt showed that the difference between the heats of formation of the colloïdal and crystalline varieties of the double phosphate is greater than +124. These experiments gave a higher value than the first series for the heat of formation of this compound, and the combined results of both series give for the heat of formation of ammonium magnesium phosphate, colloïdal, +29-3 cal.; crystalline, +419 cal. These values agree closely with the corresponding values for colloïdal and crystalline trimagnesium phosphate.

When magnesium hydrogen phosphate is in the colloïdal condition, the displacement of the third atom of hydrogen by magnesium develops only +37 cal., whilst the same substitution in the crystalline phosphate develops +144 cal. Similar phenomena are observed with calcium phosphate. In like manner, the action of ammonia on colloïdal magnesium hydrogen phosphate develops only +41 cal., whilst its action on the crystallised salt develops +146 cal., a quantity higher than that developed by magnesium, and equal to that developed by sodium or potassium. It follows that ammonium in union with magnesium forms a base, the energy of which is comparable with the energy of sodium and potassium, as already observed in the case of the chlorides and sulphates. (This vol., p. 96.) It also follows that the action of ammonia on trimagnesium phos phate will produce only a very slight thermal disturbance.

Trimagnesium phosphate is rapidly altered by ammonia with production of ammonium magnesium phosphate, not because the heats of formation of the two phosphates for the colloïdal condition are very different, but because the double salt more rapidly passes into the crystalline condition and thus develops heat. This result illustrates the fact that the more or less rapid formation of salts in the colloïdal or crystalline condition depends on the order in which the reacting substances are brought together. Ammonia also acts on crystallised trimagnesium phosphate with development of +0:42 cal., but the reaction is not complete without the addition of ammonium chloride. When this salt is added, there is a slight additional development of heat owing to the formation of a small quantity of magnesium chloride; this fact explains the effect produced by the presence of ammonium chloride when magnesium salts are precipitated by sodium phosphate. This effect is only exerted in presence of at least three equivalents of base. Ammonium chloride alone has no action on magnesium phosphate.

These facts explain the difficulty which is experienced in displacing ammonia from ammonium magnesium phosphate by means of magnesia or lime. Lime tends to produce colloïdal calcium phosphate, the heat of formation of which is less than that of the double phosphate. The heat of formation of crystallised trimagnesium phosphate is also somewhat less than that of the double compound. That decomposition takes place at all is due to the combined effect of the slight dissociation of the ammonium compound in the presence of water, especially if heated, and the volatilisation of the ammonia, which is thus removed from the sphere of action, the magnesium taking its place. C. H. B.

Saturation of Arsenic Acid by Magnesia: Formation of Ammonium Magnesium Arsenate. By C. BLAREZ (Comp. rend., 103, 1133-1135).-The developments of heat accompanying the displacement of successive atoms of hydrogen by magnesium are +14866 cal.; +11:464 cal.; +2:03 cal., giving for the total heat of neutralisation, +28.36 cal.

The heat developed by the neutralisation of arsenic acid by magnesium and ammonium is +37·645 cal., from which it follows that the displacement of the third atom of hydrogen by ammonium develops +11.30 cal. C. H. B.

Heat of Formation of Potassium Methoxide and Ethoxide. By DE FORCRAND (Compt. rend., 103, 1263–1266).—Potassium methoxide is obtained by dissolving potassium in excess of anhydrous methyl alcohol and heating the solution in a current of pure dry hydrogen at 200°. Complex alcoholates similar to those formed by sodium are at first formed. The heat of solution at 12° is +11·74 cal.

CHOH liq. + K2O solid = CH, OK solid +

H2O solid...

develops 24-79 cal.

A

Potassium ethoxide is obtained in a precisely similar manner. small quantity of crystals of the compound EtKO + 3EtOH was obtained. Heat of solution of the ethoxide at 12-15° = +14·70 cal.

C2H, OH liq. + K2O solid = C2H, OK solid

5

develops + 22:28 cal.

The values for the potassium compounds agree very closely with those obtained previously for the sodium compounds, and the values are practically the same with both ethyl and methyl alcohol. Moreover the values corresponding with the action of potassium and potassium hydroxide on the two alcohols agree closely with those corresponding with their action on water.

In the case of sodium the differences between the heat developed

by its action on the two alcohols respectively, and on water, are much greater than the corresponding differences in the case of potassium, and the absolute values of the quantities are higher with sodium, a result which is due to the fact that the tendency to form polyalcoholic alcoholates is much greater in the case of sodium. Moreover, the heats of formation of the hydrates of potassium hydroxide are much greater than those of the corresponding sodium compounds.

It follows that the alcoholates of potassium ethoxide or methoxide dissolved in the alcohols are practically in the same condition as potassium hydroxide dissolved in water, whilst the dissociation of sodium hydroxide in water is much greater than that of sodium methoxide and ethoxide in the alcohols.

C. H. B.

Heats of Neutralisation of Glyceric and Camphoric Acids. By H. GAL and E. WERNER (Compt. rend., 103, 1199-1200).Glyceric Acid, OH CH, CH(OH) COOH.-Heats of neutralisation by the first and second equivalent of potassium hydroxide respectively +11-334 cal. and +12.127 cal.; total +23-461 cal. The addition of a third equivalent of alkali causes no further thermal disturbance.

Camphoric Acid, CsH1(COOH)2.-Heats of neutralisation by the first, second, and third equivalents of sodium hydroxide respectively, +13-828 cal.; +13·253 cal.; +00 cal.; total +27.081 cal.

These results confirm the former conclusion that the total heat of neutralisation of hydroxy-acids is lower than that of acids into which the hydroxyl-group has not been introduced. C. H. B.

Heats of Neutralisation of Malic and Citric Acids and their Pyrogenic Derivatives. By H. GAL and E. WERNER (Compt. rend., 103, 1019-1022).

The heat developed by neutralisation is practically the same for each acid function of the same acid.

In all cases, with the exception of itaconic acid, the heat of neutralisation of the pyrogenic derivatives is about 2 cal. greater than that of the generating acid, a relation similar to that already observed in the case of monobasic acids and the corresponding hydroxy-acids (this vol., p. 96). The pyrogenic acids derived from malic acid by the loss of H2O, and from citric acid by the loss of CO2+ H2O, no longer contain the hydroxyl-group. C. H. B.

VOL. LII.

Ρ

Heat of Neutralisation of Meconic and Mellitic Acids. By H. GAL and E. WERNER (Compt. rend., 103, 1141-1142).-The heat developed by the action of successive equivalents of sodium hydroxide on meconic acid, OH.C.(COOH), is +14-074 cal.; +13.611 cal.; +8′369 cal.; +1·328 cal. = 37.382 cal.

The heat developed by the action of sodium hydroxide on mellitic acid, C.(COOH)e, is +15.040 cal.; +15.516 cal.; +15294 cal.; +13 713 cal.; +12·793 cal.; +11.678 cal. 84.034 cal.

=

The heat of neutralisation of meconic acid is less than that of mellitic acid, probably because the former is a hydroxy-acid. In both cases the heat of neutralisation diminishes as neutralisation becomes more complete. The values for mellitic acid show that if neutral sodium mellitate is evaporated with excess of hydrochloric acid, it will lose part of the base and yield an acid salt, and the same acid salt will be obtained, when mellitic acid is heated with a solution of an alkaline chloride. The values obtained for mellitic acid are analogous to those found for phosphoric, sulphuric, and other acids in which several hydroxyl-groups are united with the same radicle.

The numbers for the six acid functions of mellitic acid differ more widely than would have been expected from the symmetrical constitution generally assigned to this acid. C. H. B.

Temperature Regulator. By G. W. A. KAHLBAUM (Ber., 19, 2860-2862). An improvement on Andrew's form (Ann. Phys. Chem. [2], 4, 164).

Influence of Change of Atmospheric Pressure on Boiling Point. By G. W. A. KAHLBAUM (Ber., 19, 3098-3101).—With the exception of Broch's "Températures d'ébullition de l'eau pure' (Trav. et Mém. Bureau Internat. des Poids et Mes., I., A., 43 (1881)), calculated from Regnault's observations (Mém. Acad. Sci., 21 (1847)), accurate determinations of boiling point at regular intervals of pressure have not been made.

The author has made such a series of measurements for ether (sp. gr. 0-720). The ether was boiled in a platinum vessel, the heating being as uniform as possible; and to avoid possible change of the zero point of the thermometer, the latter was wrapped in wadding and transferred to a vessel of boiling ether after each observation. It was thus maintained at about the same temperature for a period of four months. The author strongly recommends this device. By graphic interpolation, the boiling points were calculated for each mm. of pressure from 721 to 750, and are given in tabular form. Only relative, not absolute, accuracy is claimed for them.

A comparison of this table with Broch's shows that within the ordinary limits of variation of atmospheric pressure, the curves of boiling point for water and ether are practically parallel. Assuming this to be true for other liquids whose boiling point may exceed 100° by as much as that of ether falls below it, the author gives a table of corrections of observed boiling point for each mm. pressure, for liquids boiling between 30° and 170°, of which the following is a condensed form

or a mean of 1° for each 2.69 mm.

770-780

= -0.036

This agrees with Kopp's result, 1° = 2.7 mm. (Annalen, 34, 266); Landolt's slightly higher figure, 0·043° = 1 mm. (Annalen, Suppl. Bd. 6, 175), was calculated for lower pressures.

CH. B.

By

Boiling Points of the Fatty Acids, C2H4O2-C5H1002. G. W. A. KAHLBAUM (Ber., 19, 2863-2865).—The author compares his published results with those obtained by Ramsay and Young (Abstr., 1886, 965), and by Richardson (Trans., 1886, 761), and points out their close agreement for pressures varying between 5 and 50 mm. This he regards as sufficient answer to the criticisms of Ramsay and Young. W. P. W.

Vapour-tensions of Ethereal Solutions. By E. RAOULT (Compt. rend., 103, 1125-1127).-The author has carefully measured the vapour-tensions of ethereal solutions of several organic compounds at different temperatures.

Between 0 and 25°, the difference between the vapour-tension of the ethereal solution and that of the ether is exactly proportional to the vapour-tension of pure ether at the particular temperature. For solutions containing from 1 to 5 mols. of the substance in 5000 grams of ether, the difference between the vapour-tension of the solution and that of pure ether is proportional to the amount of solid in solution. The relative diminution of the vapour-tension caused by the solution of 1 gram of the substance in 100 grams of ether depends on the nature of the substance. The molecular reduction of the vapourƒ + ƒ M tension k is obtained by the formula k X in which ƒ is ƒ P' the vapour-tension of ether, f the vapour-tension of the solution, M the molecular weight of the substance, and P the amount dissolved in 100 grams of ether. It is found that if a gram-molecule of any compound whatever is dissolved in 100 grams of ether, the vapourtension of the ether is diminished by a constant fraction of its normal value. For all temperatures between 0° and 25°, the value of this fraction is 0.71.

=

C. H. B.

Apparatus for Measuring the Tension of Vapours. By G. W. A. KAHLBAUM (Ber., 19, 2954-2958).—The essential point in this apparatus is the maintenance of a uniform temperature by the circulation of a current of water heated in a vessel exterior to the jacket. W. P. W.

Dissociation of Salts containing Water of Crystallisation. By W. MÜLLER- ERZBACH (Ber., 19, 2874-2876).-A continuation of the author's experiments (Abstr., 1885, 952; 1886, 10) in which the relative vapour-tensions of the water in the salts and of pure water are compared. The following salts are examined: CaN,O. + 4H2O,