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mmm THE CHEMICAL NEWS, Vol. I. No. 18.—April 7, i860. SCIENTIFIC AND ANALYTICAL CHEMISTRY. Notes on Boiling-Points, by Arthur H. Church, F.C.S. One great difficulty besets all attempts at drawing cor rect conclusions concerning the boiling-points of homo- logues, isomers, ruetamers, &c., the determination of boiling-points being of necessity referred to an arbitrary barometric pressure. The alteration in boiling-point, consequent upon an alteration of pressure, is by no means the same for all liquids. Then, too, the determination is often made somewhat carelessly: perhaps the pressure is not noted at all, or the thermometer is incorrect, or the presence of moisture is not guarded against; or maybe the substance itself is not pure; finally, oxidation of the substance may occur from the action of the atmospheric air in the heated vessel. From time to time, however, some very interesting relations between the boiling-points of various organic, substances have been pointed out, chiefly by Kopp. One thing is certain, that under a pressure of 760 mm. the elevation in boiling-point for an increment of GIL, is not the same for all homologous series, and it seems probable that it is not of equal value in different parts of the same series. It is remarkable that the substitution of 1 eq. of methyle for the 1 eq. of basic hydrogen in the series of acids of which formic acid is the first member, reduces the boiling-point by about 63° 0. for this substitution is really the addition of GH 2 . If for the basic hydrogen of formic acid we substitute ethyle, the boiling-point is lowered 4q°7, or 63°—18°'3. A similar relation may be observed between water (hydric acid, or hydrate of hydrogen) and its ethyle derivatives, alcohol and ether : Boiling-point. Difference. Water, H, IIO . . . ioo 0, o, 0 Alcohol, © 2 II,, H© . . 7 8°’5J ' * 21 ‘ S Ether, G 2 CLh,© . . 35°'S } ' ' 215x2 Here the substitution of G 2 H_ for II in water (really the addition of 20H 2 ), reduces the boiling-point 2i 0- 5, while the substitution of a second eq. of H. by a second eq. of 0„H., which is the introduction of another 2GH„ lowers the boiling-point by twice that amount. Also, where 1 eq. of II in hydrate of ethyle is replaced by methyle, the boiling-point is lowered about 63°. Re placement of the II of HC1, and of Nil,, types of other classes of chemical compounds by organic groups, in stead of reducing the boiling-point raises it. On careful collation of all the boiling-points of organic substances which have been accurately determined, it seems that a difference in composition of GIT,, however caused, is indicated in homologues by a difference of boiling-point which seldom or never exceeds 27, and is scarcely ever less than 9 degrees centigrade. Whatever the reason, the actual numbers for the various series ex hibit considerable fluctuations, as the following instances show: — Radicals Hydrates Cyanides Nitrates Formiates Acetates Butyrates Valerates Oxalates Acids of the formic series . . 2o 0, o; Anhydrides „ . . 12 - j Benzole series . . . . 22 '3 But it is perhaps among the boiling-points of com pounds containing nitrogen, and especially among the organic bases, that we find the most singular relations. On comparing the cyanides of ethyle, butyle and amyle, we find that the difference in boiling-point for GH, is as much as 21 0 : — Boiling-point. 82° 1 . .46° j Cyanides of • Ethyle Amyle Butyle Amyle 125 I i+6° J And in the series of bases of which pyridine is the first term nearly the same values for GH, are obtained. Pyridine Picoline I.utidine . Collidine Parvoline Boiling-point. 1 55 . 178° 198° Aniline Boiling-p 182° Methylaniline • • l 93° Ethylaniline 204° Propylauiline 215 0 ' Toluidine . 198°. Methyltoluidine . . . 208°) Etbyltoluidine . 2i8°’5' The mean here is about zoV But in the aniline series, which is isOtneric with that of pyridine, the highest value assignable to GH, is 16°, and if reliance may be placed upon the boiling-points given as those of the higher terms of the series, the increment as we ascend is reduced as low as 12 0 . As aniline and its homologues constitute the starting-point of numerous other homologous series, such as those of methyl-aniline, methylrtoluidine, &c, we may expect that the boiling- points of the various members of these series, if accu rately determined, will afford us some light as to the influence on the boiling-point of the various forms in which the increment GH, has been introduced. On comparing the methyle and ethyle derivatives of aniline and toluiSine, and also of piperidine, a tolerably regular increment of ll° for each addition of GH, is observ-