solidified again, showing the formation of a compound of higher melting point than either. This was found to be but sparingly soluble in most ordinary solvents, such as alcohol, ether, benzene, &c. After previously washing well with ether to remove phenol, it was recrystallised from glacial acetic acid, as this solvent seemed to be the best. A large quantity of acetic acid was required. After a second recrystallisation, the carbamate was obtained in beautiful crystalline tables. These were washed with ether many times to remove acetic acid, dried, and finally submitted to analysis. Calculated for Found. N..... 6.60 6.84 The melting point was about 240°, but was difficult to determine with precision, as the substance decomposes with evolution of gas at about the same temperature. Metatoluylenediamine, CH,C,H,(NH2)2, was next treated with phosgene metatoluylene diisocyanate, CH,(CH3)(NCO), = [1 : 2 : 4], was thus obtained. Toluylenediamine hydrochloride was treated with phosgene in an exactly similar manner to that described for obtaining diphenyl dicyanate, viz., successively in benzoic acid and diphenylamine vapour-baths. The toluylene dicyanate passed over as a paleyellow liquid, which solidified to groups of needles almost perfectly white. The needles were smaller than those of diphenylene dicyanate. The compound as thus collected was almost pure, although contaminated to a slight extent with hydrochloric acid, which conld not be readily removed. The melting point was 94°. On distilling the substance, it lost hydrochloric acid, and though it passed over mainly unchanged, was in part decomposed, the melting point being considerably lowered. N Calculated for Found. It was soluble in ether, and possessed the strong and unpleasant odour of phenyl cyanate, especially noticeable on gently heating. Thus, in all its properties this compound corresponds to, and is evidently identical with, that described by Lussi (Ber., 7, 1263, and 8, 291). He obtained in the first place the corresponding urethane, by treating toluylenediamine with ethyl chlorocarbonate, and then distilled this urethane with phosphoric anhydride. In order to confirm the identity, a portion of the cyanate, as prepared by me, was boiled with alcohol, and on allowing it to stand, white silky needles separated. These were soluble in ether, and melted at 135°. These VOL. XLIX. T properties agree with the description of the urethane given by Lassi. For complete control, a small quantity was prepared as described by him from ethyl chlorocarbonate and metatoluylenediamine, recrystallising the product from alcohol. I thus obtained exactly similar lustrous needles, melting at 135°; they gave the following results on analysis: N...... Calculated for Found. 10.53 10.64 Lussi states the melting point to be 137°. I converted another portion of the cyanate into the phenol carbamate. Diphenyl-loluylene Dicarbamate, CH3(CH1)(NH·COOC6H3)2= Metatoluylene isocyanate, as prepared above, was heated with an excess of phenol in an oil-bath at from 130° to 150° for half an hour. A gelatinous mass was obtained, which when boiled with ether to remove phenol, became changed into a gray powder. This was recrystallised from hot glacial acetic acid in which it readily dissolved. Clusters of white needles separated on cooling. These were collected, well washed with ether to remove excess of acetic acid, and dried at 105°. The compound was slightly soluble in alcohol and ether and melted at 147.5°. N.... Calculated for 7.73 Found. 7.87 The next attempt which was made was to treat orthotoluylenediamine with phosgene. I did not succeed, however, in obtaining any cyanate in this case. It was recently noticed by Gattermann and Wrampelmeyer, that whilst para- and meta-phenylenediamine are each converted respectively by phosgene into the corresponding cyanates, orthophenylenediamine is not. Their experience and my own may probably be explained by the suggestion that the orthodiamine is first converted into an ortho-substituted carbamide, and that then the NH-groups are held so firmly by the CO-group as not to permit of further decomposition by phosgene. Thus, in the above case, the reaction is probably NH2 C.H.(CH)<NH NH. + COC12 = 2HCl + CH3(CH)<>co. But the compound refuses to be further converted into the corre sponding dicyanate, as is the case when the NH-groups are attached to carbon-atoms further apart in the benzene-ring. The corresponding urethanes which would result from the action of alcohol on these cyanates, can, however, be prepared by the action of ethyl chlorocarbonate on the amines. Orthophenylene-diurethane, CH,(NH·COOC2Hs)2 = [1:2], was prepared in this way. Orthophenylenediamine was heated with an excess of ethyl chlorocarbonate at 130°, the unaltered ethyl chlorocarbonate distilled off, and the residue washed with water and hydrochloric acid. By recrystallisation from alcohol, after previously boiling the solution with charcoal, lustrous needles melting at 88° were obtained. The dried compound was submitted to analysis. N .... Calculated for 11.11 Found. Orthotoluylenediamine also reacted with ethyl chlorocarbonate, and crystals separated from the alcoholic extract of the product. I have not as yet purified and analysed this compound. Lastly phenylhydrazine was treated with phosgene. The latter was conducted over phenylhydrazine hydrochloride, heated at 220° to 230° in a paraffin-bath. Towards the close of the operation, the temperature was allowed to rise to 250°. A pale-brown oil distilled over, and solidified on cooling to a pasty mass. The product of the reaction possessed the powerful odour of phenyl cyanate, and the vapour strongly attacked the eyes. On heating it in a fractional distillation flask, hydrogen chloride was evolved, and a portion sublimed in splendid long needles. Pressed out on porcelain, it gradually but entirely sank into the plate. Instead of the reaction taking place as I hoped, according to the equation— CHNHANH, + COCl = CH NH NCO + 2HC, a solid combination of phenyl cyanate and hydrochloric acid had been formed. That phenyl cyanate has the property of dissolving large quantities of hydrogen chloride to form a solid mass is mentioned by Hentschel (Ber., 17, 1285, and 18, 1178). That this curious combination had taken place in this case was shown by the evolution of hydrogen chloride on heating the product; by the continued characteristic and unpleasant odour of phenyl cyanate, which was so unbearable that it could not be worked with for longer than a few minutes consecutively, and lastly by its conversion into carbanilide. This was effected by simply boiling with water in a flask provided with a reflux condenser until the odour of phenyl cyanate had disappeared. The crystalline needles thus formed, after recrystallisation from alcohol, were shown to have the same melting point and percentage of nitrogen as carbanilide. Phenyl cyanate, as is well known, is readily converted into carbanilide by the action of water. The experiment did not allow me to determine whether phenylhydrazine was at first decomposed, yielding aniline, which, together with phosgene gave phenyl cyanate, or whether the cyanate, C.H, NH-NCO, I had expected to obtain was first formed, but then decomposed, yielding phenyl cyanate. I have much pleasure in taking this opportunity to express my best thanks to Dr. Gattermann, for valuable counsel afforded by him to me during the course of the work above described. Chemical Laboratory, University of Göttingen. XXIX.-The Influence of Temperature on the Heat of Chemical Combination. By SPENCER U. PICKERING, M.A., Professor of Chemistry at Bedford College. OUR knowledge of the influence which temperature exerts on the heat of chemical combination is at present of the most rudimentary character. It has been established as one of the fundamental principles of thermochemistry that the total heat evolved in the combination of two substances at different temperatures, together with that necessary to reduce the systems in the two cases to the same initial and final temperatures, is a constant quantity-that where Q and Q' represent the actual heat evolved during the combination of A with B at T and T', we shall have· T), T) Q' (C1 + CB) (T' Q-CAB(T' T) AB = CA, CB, and CAв being the specific heats of A, B, and the compound which they form, respectively. Where the specific heat of the compound is equal to the sum of those of its components, the heat which these develop in combining will be a constant quantity independent of temperature. The labours of Kopp have shown that such a condition exists to a certain extent in the case of most solids, but we are still in ignorance as to whether it is absolutely or only approximately true, whether those variations which have in many cases been observed in the specific heats of solids are regular in their nature, whether, in fine, the compound AB at T is in every respect the same substance as AB at T'. The present investigation shows that this is not the case. It will appear that the relation between the constituent portions of the molecule of a complex solid undergoes a series of modifications as the temperature changes, the result of which is that the variations exhibited in the heat of combination, and consequently in the specific heat also, being conditioned by a different order of circumstances at different temperatures, exhibit irregularities of a very marked cha racter. As no methods have yet been devised for obtaining very accurate measurements of specific heats through small, or indeed through considerable ranges of temperature, the heat of combination appeared to be the only available means of investigating the subject; in order, however, to invest the determinations of it with a degree of accuracy which would promise any chance of success, it was necessary to confine them within the limits of ordinary atmospheric temperatures, a small range of 25° C. only being thus available. Substances which would be most likely to exhibit any variation in the heat of their formation within these narrow limits would be those in which the energy of combination was small. Hydrated salts afford many instances of such a nature, and, consequently, they were chosen as the subjects of this investigation; the heat of hydration presents, moreover, one other material recommendation for the present purpose, in that the number of operations necessary for a determination of it is very limited, and the nature of these is very simple. Whatever may be the complexity of the reactions occurring when a salt is dissolved in water, it is generally accepted that the difference between its heat of dissolution in the anhydrous and hydrated state gives the heat of combination of the salt with its water of crystallisation, provided we first subtract from the second of the above-named quantities the heat absorbed in the conversion of the solid water present into liquid water, for every fact which bears on the question supports the view that in a solid hydrated salt the water is present as a solid, and in the solution of such a salt as a liquid. The heat of fusion of ice at temperatures other than 0° never having been determined experimentally, it must be calculated by means of the specific heats of water and ice; the latter of these has also never been determined for temperatures above 0°, and, consequently, some doubt must be felt as to the correctness of the values calculated for the heat of fusion. The present experiments themselves, however, will be found to afford considerable evidence as to the accuracy of these calculated values, and, moreover, any error in them will not affect the main conclusions drawn from this work, This can only be so if the heat of combination of the various atoms composing the salt molecule is unaffected by the combination of that molecule with the water. |