93 General and Physical Chemistry. Chemical Changes produced by Sunlight. By E. DUCLAUX (Compt. rend., 103, 881-882).—Many organic compounds are affected by solar radiation in the same way as by microbes, the products of the change being water and carbonic anhydride, with other substances which are relatively stable in the conditions under which they are produced, and are identical with the products of the action of microbes. Cane-sugar in neutral or alkaline solution is not affected by prolonged exposure to sunlight, but if slightly acidified even with an organic acid it is readily inverted by solar radiation. The solution of invert sugar undergoes no further change so long as it remains acid, but if made alkaline the glucose is rapidly decomposed with formation of water, carbonic anhydride, oxalic, formic, and acetic acids, and about 3 per cent. of alcohol. A similar change takes place, although less rapidly, out of contact with the air, and hence it is evident that the decomposition is due to internal combustion. Lactose and lactates also yield alcohol under similar conditions. The exact nature of the change in any case is modified by the nature of the source from which oxygen is absorbed (air, salts of platinum, gold, mercury); but the chief products are practically the same from all substances. These products are alcohol, oxalic acid, acids of the acetic series, leucine, carbamide, carbonic anhydride, water, &c. Certain differences are, however, observed. Tartaric acid gives aldehyde in place of alcohol, and the alcohols, if oxidation is regular, tend to produce the corresponding acid of the acetic series. C. H. B. By Practical Methods of Photographing the Spectrum. J. M. EDER (Monatsh. Chem., 7, 429-454). This paper contains a description of some practical methods of photographing the various parts of the spectrum by silver bromide gelatin plates sensitised by different dyes. The preparation of the plates and the processes used for the development are described in full, and accompanied by copies of photographs taken. For spectra from the ultra-violet to the yellow, about D, the best dyes are erythrosin, benzopurpurin 4B, and quinoline-red; from the ultra-violet to the red cyanin, is the best; from the orange to the red, cœrulein with red glass, and "sensitive green," a dye from parahydroxybenzaldehyde and dimethylaniline, are recommended. These plates, sensitive to the green, yellow, or red part of the spectrum, are suitable for photography by petroleum and gas light, and for taking photographs of gilded documents and papyri, of microscopic preparations, and of clouds on a blue sky, interposing yellow glass to subdue the blue. Excellent photographs of stars have been taken with the aid of these plates. V. H. V. VOL. LII. h Electrolysis of Carbon Compounds. By J. HABERMANN (Monatsh. Chem., 7, 529-551).-In continuation of former experiments on the electrolysis of carbon compounds (Abstr., 1881, 215), the author describes the results which are obtained under various conditions with alcohol acidified with sulphuric acid, or rendered alkaline by soda, and with potassium acetate dissolved in methyl alcohol or its homologues. The sources of electrical energy used were a thermobattery of 120 elements, a Smee's battery of 16 elements, and a dynamomachine of one horse-power. On electrolysis, alcohol acidified with sulphuric acid yields hydrogen evolved as gas at the negative pole, aldehyde, and after prolonged action aldehyde-resin together with ethyl hydrogen sulphate. The main reaction is therefore C2H,O= С2H ̧O + H2. If the alcohol is rendered alkaline, or is in the form of sodium ethoxide, the products of decomposition are hydrogen, carbonic anhydride as sodium carbonate, an aldehyde-resin insoluble in ether and alcohol, together with a soluble modification, and a substance allied to cinnamaldehyde. A concentrated solution of potassium acetate in ethyl alcohol yields a mixture of hydrogen and ethane together with potassium ethyl carbonate, by the mutual decomposition of the salt and acid. In fact, the process serves as a convenient method for the preparation of potassium ethyl carbonate in large quantities, as the salt separates in fine crystalline aggregates. It is quickly decomposed by water, but dissolves in absolute alcohol without change. The results obtained with solutions of potassium acetate in methyl and butyl alcohols were unsatisfactory. V. H. V. Phosphates. By BERTHELOT (Compt. rend., 103, 911-917).— When ammonium chloride is added to a solution of trisodium phosphate there is an absorption of heat which varies with the proportion of ammonium chloride, being 5.96, 5.63, 4.84, and 2.62 cal. for 3, 2, 1 and mols. of ammonium chloride respectively. Complete decomposition of the sodium phosphate would correspond with absorption of heat equal to -64 cal., and hence it is evident that the action of the ammonium chloride is almost complete, although the water exerts a greater dissociating effect on the ammonium phosphate than on the sodium salt. an If trisodium phosphate is added to a solution of a magnesium, barium, strontium, calcium, or manganese salt, a colloïdal precipitate of the insoluble phosphate is at first formed, and there is considerable absorption of heat, but after some minutes the precipitate becomes crystalline and a large quantity of heat is developed. The heats of formation of the colloïdal and crystallised phosphates are given in the following table: Colloïdal. Barium phosphate.. 68.4 Crystallised. Strontium phosphate Calcium phosphate Manganes phosphate .. In the case of barium phosphate, the sodium phosphate must be added to the barium chloride, and not vice versa, otherwise the change to the crystalline state is too rapid. The phenomena now described explain the discordant results obtained by Louguinine and the author for the heat of neutralisation of phosphoric acid by baryta, and also the differences observed by Blarez (this vol., p. 7) between the heats of formation of barium phosphate and barium arsenate. In the case of strontium also, the change to the crystalline condition is extremely rapid, if the strontium solution is poured into that of the trisodium phosphate. Calcium phosphate was obtained only in the colloïdal form. The heats of formation of the colloïdal insoluble phosphates do not differ to any great extent from the heat of formation of an equivalent quantity of trisodium phosphate, 33.6 × 2 cal. In other words, the precipitate in its initial condition corresponds closely with the soluble salt from which it has been derived, a further example of the tendency of systems which are undergoing transformation to preserve their molecular type. On the other hand, the new phosphates may be dissociated by water to a greater extent than the soluble phosphate from which they have been formed; and this dissociation will be accompanied by an absorption of heat. This absorption is practically nil with barium phosphate, which approximates closely to the alkaline phosphates, but it is very distinct with magnesium phosphate, which is more readily dissociated. In dissolved trisodium phosphate, the third and even the second equivalents of the base are less intimately combined with the acid than the first atom, and are partially separated from it by the dissociating action of the solvent. There can be little doubt that this imperfect state of combination also exists in the colloïdal insoluble phosphates, the formation of which is due to a polyalcoholic rather than an acid function of the phosphoric acid. The combination, however, soon becomes more intimate, and the alcoholic function changes to an acidic function comparable with that of ordinary tribasic acids, the change being accompanied by development of heat and crystallisation of the phosphates. The actual development of heat is much greater than can be supposed to be due to the mere physical change from the colloïdal to the crystalline condition, even if the change were accompanied by combination with water. As a matter of fact, the crystallised phosphate contains less water than the colloidal phosphate. In their new condition, the heats of formation of the insoluble phosphates become practically treble that of the ordinary monophosphates, or in other words, the three acid functions become equivalent to one another, and to this change is due the greater proportion of the heat developed in the passage from the colloïdal to the crystalline form. C. H. B. Heats of Neutralisation of Homologous and Isomeric Acids. By H. GAL and E. WERNER (Compt. rend., 103, 806-809).-The author has determined the heats of neutralisation of isobutyric, isopropylacetic, trimethylacetic (pivalic), caproic, isobutylacetic, and sorbic acids, and his results, together with the heats of neutralisation of the lower acids of the acetic series, as determined by Berthelot, Louguinine, and others, are given in the following table. Heat of solution of isobutyric acid, directly+0.973 cal., indirectly + 1.012 cal.; isopropylacetic acid, directly +1.167, indirectly + 1.030. Isobutyric acid, CHMe, COOн.. Normal valeric acid, CH,Me CH2 CH2COOH. Isopropylacetic acid, CHMe, CH2COOH . Trimethylacetic acid, CMe, COOH Normal caproic acid, CH,Me CH2 CH2 CH2COOH . Heat of neutralisation. 13.3 13.4 14.3 14.4 13.9 14.4 14.4 13.674 14.689 14.5 Omitting formic and acetic acids, the heat of neutralisation of the other acids, with the exception of isobutyric and trimethylacetic acids, is practically constant, and varies between 14:3 and 146. Isobutyric acid is a secondary acid, and trimethylacetic acid is a tertiary acid, and it would seem therefore that the heat of neutralisation of primary acids is greater than that of secondary acids, whilst that of tertiary acids is somewhat smaller still. The heat of neutralisation of sorbic acid, which is regarded by Menschutkin as a tertiary acid, is 12-945. C. H. B. Heats of Neutralisation of Malonic, Tartronic, and Malic Acids. By H. GAL and E. WERNER (Compt. rend., 103, 871-873).— Malonic Acid.-Heat of solution at 10°-4.573 cal. Heat of neutralisation by soda: 1st equivalent, 13.342 cal.; 2nd equivalent, 13.778 cal.; total, 27·120 cal. Tartronic Acid.-Heat of solution at 12° = -4·331 cal. Heat of neutralisation by soda: 1st equivalent, 13 711 cal.; 2nd equivalent, 11.856 cal.; 3rd equivalent, 0·0 cal.; total, 25-567. Malic Acid.-Heat of solution at 20° = −3·148 cal. Heat of neutralisation by soda: 1st equivalent, 12.730 cal.; 2nd equivalent, 12-189 cal.; 3rd equivalent, 0-0 cal.; total, 24.919. The heat of neutralisation of oxalic acid is 28.1 cal. (Berthelot and Thomsen); of succinic acid, 264 cal. (Chroutschoff); and tartaric acid, 253 cal. (Berthelot). It is evident from these values that the heat of neutralisation diminishes as the molecular weight increases. The introduction of the OH group into oxalic, malonic, and succinic acids lowers the heat of neutralisation by about 2 cal. A similar difference has previously been observed between propionic and lactic acids, and between benzoic and the hydroxybenzoic acids. C. H. B. Thermochemistry of Reactions between Magnesium Salts and Ammonia. By BERTHELOT (Compt. rend., 103, 844-848).— When magnesium sulphate solution is mixed with an equivalent quantity of sodium hydroxide solution, there is an immediate develop ment of +0.18 cal., but the development of heat gradually slackens, and at the end of 10 minutes is + 114 cal. The successive developments of heat are due to the fact that a basic salt is first formed, which is afterwards decomposed by the soda, and also to the hydration, contraction, &c., of the precipitate. Magnesium chloride and sodium hydroxide behave in like manner. At first there is an absorption of 0.32 cal., and afterwards a development of +0.32 cal., the final result being nil. It is evident, as the researches of Thomsen, Favre and Silbermann, Ditte, and others have already indicated, that the heat developed by the action of acids on magnesium hydroxide approximates closely to that developed by their action on potash and soda. The action of ammonia on magnesium sulphate is accompanied by an absorption of -0.24 cal, whereas if the magnesium were completely displaced, 30 cal. should be absorbed. The difference is due to the formation of double salts or oxides, the production of which is accompanied by a development of +28 cal. With magnesium chloride, the difference between the calculated and observed values is +2.2 cal. If magnesium sulphate is mixed with 2 mols. of ammonium chloride, +0-32 cal. is developed, and if an equivalent quantity of ammonia is now added, there is a further development of +0.26 cal., the total development of +0.58 cal. being due to the formation of a complex oxide, the heat of neutralisation of which is 0-58 cal. higher than the sum of the heats of neutralisation of magnesium oxide and ammonia separately. When magnesium chloride is mixed with ammonia, there is an absorption of -0.48 cal., and if ammonium chloride is then added there is a development of +0.56 cal., the sum being 0.08 cal., from which it follows that the heat of neutralisation of the complex oxide by hydrochloric acid is practically identical with that of magnesium oxide. If magnesium sulphate or chloride solution is mixed with sodium. hydroxide, and ammonia then added, the greater part of the precipitate redissolves, but there is no sensible thermal disturbance, a result which indicates that the heat of solution of the precipitate is identical with its heat of combination with the solvent. If, on the other hand, magnesium sulphate is first mixed with ammonia, and the sodium hydroxide added afterwards, there is a development of +1.90 cal., probably due to the fact that, the order of admixture being reversed, the liquid requires a much longer time to attain the same condition. The difference between the observed thermal disturbance and the development of heat resulting from the action of soda or magnesium sulphate alone is a further proof of the formation of complex compounds. If magnesium sulphate is mixed with 2 mols. of ammonium chloride and sodium hydroxide then added, +364 cal. are developed, and some permanent precipitate is formed. The thermal disturbance is greater than that which would correspond with the displacement of ammonium by sodium, and the difference indicates the combination of magnesia and ammonia with formation of ammonio-magnesium sulphate. If 4 mols. of ammonium chloride are added at the begin |