a mixture of oil of cloves and linseed-oil, and this was gradually raised to 110° or 115°; and the water did not burst into vapour unless it touched the sides of the vessel or the thermometer. The smallest globules of water bore the higher temperatures best: those of 10 millims. diameter were raised to 120° or 130° C.; while those of from 1 to 3 millims. were raised to 178°, when the vapour has an elastic force of 8 or 9 atmospheres*. 26. Solids brought into contact with the globules liberated vapour with a hissing noise. Porous bodies, such as wood, chalk, cotton, paper, &c., produced this effect best. A glass rod or a metallic wire did not always act in this way. A platinum wire by frequent use appeared to lose the power of causing sudden vaporizationt. Porous bodies act best because they carry down air in which the globule begins to evaporate and expand. 27. M. Dufour rejects the theory which attributes the retardation in boiling to the adhesion of the liquid to the sides of the vessel. The contact of solids may prevent the liquid from rising above its boiling-point. The real explanation is to be found in the molecular relations of liquids—in a sort of internal cohesion. When a liquid is near the boiling-point, these molecular influences act as excitants to change of state. The adhesion to the sides of a vessel also excites a peculiar molecular condition in the liquid, and it is at the sides that this molecular equilibrium is disturbed and boiling takes place. But when the aqueous globule is immersed in a fluid with which water does not mix and is raised to a high temperature, it is the contact of a solid that disturbs the mechanical structure of the globule and induces change of state. Heat alone, acting on water protected from the air, contact of solids, and other disturbers of the molecular condition, cannot produce change of state, except very much above the temperature usually recognized as the boiling-point. But M. Dufour admits that the molecular influences or disturbers unfortunately present so many irregularities, that they have hitherto escaped the controlling action of any regular law. He thinks there must be some other force besides cohesion that * I have no doubt that the globules were in the spheroidal state, as in De Luc's experiment (7, note *, p 165). More than thirty years ago I published in my Student's Manual of Natural Philosophy,' p. 553, an account of some experiments in which water, alcohol, ether, and some other liquids were gently delivered from a dropping-tube to the surface of a fixed oil heated to 450° or 500° F. The liquid drops rolled about on the surface in the spheroidal state; and in some cases, when a drop slipped beneath the surface, it exploded and scattered the oil about; but in other cases it was shot up again to the surface, where it continued to roll about as before. † Dufour says in another part of his memoir that glass is less active as a promoter of vaporization than metal. "Il semble que le fréquent usage d'une pointe de platine contribue à l'amener à cette sorte de passivité." delays the boiling of a liquid; "but these and numerous other phenomena which depend on mechanical molecularity are in a deplorable state of obscurity." He thinks that Gay-Lussac (8) uses the word cohesion in a wider sense than that which opposes the separation of particles. "We must simply conceive that the force which prevents the vapour from forming is an internal force due doubtless to cohesion of the liquid, which the vapour must overcome, and that resistance to change of state which it is more difficult to analyze." 28. In 1864 and the following year M. Dufour published two further memoirs* on the phenomena of boiling water, in which he shows that under certain conditions the retardation of the boiling-point takes place at reduced pressures and under atmospheres of hydrogen, street gas, and carbonic acid. As to the action of solids in promoting boiling, he has no doubt that it is due to the air adhering to them, and they become inactive when this air is removed by the boiling water-and that when the boiling-point of water rises by repeated boiling, the effect is due to the expulsion of air (11). Bits of dry pine-wood, paper, filaments of cotton, &c. lowered the boiling-point. "Soustraits depuis longtemps au contact de l'air, fréquemment et longuement chauffés dans l'eau, ils avaient fini par devenir absolument inactifs jamais une bulle de vapeur ne se produisait plus sur leur surface, et des retards considérables d'ébullition pouvaient se manifester" (p. 210). 29. It will be seen from these historical notices that much importance is attached to the influence of dissolved air upon the boiling of liquids, as pointed out by De Luc (7) nearly a century ago, and more recently insisted on by Donny (21) and others. It is generally admitted in our text-books (1st) that as soon as this dissolved air has been expelled by heat, liquids boil with difficulty, or produce only sudden flashes of steam; (2nd) that those liquids which have only a weak affinity for air, such as sulphuric acid, alcohol, ether, &c., boil with the greatest difficulty; (3rd) that the mutual cohesion of the molecules of the liquid, and the adhesion of the liquid to the sides of the vessel, influence the boiling-point, but the adhesion varies with the nature of the vessel and the condition of its sides as to roughness or smoothness; (4th) that the action of solid substances in promoting tranquil boiling and in preventing soubresauts is by carrying down air. 30. My reasons for dissenting from these conclusions are given in my paper published in the Proceedings of the Royal Society (21, note), to which I beg to refer. * Archives des Sciences, Bib. Univ. vol. xxi. p. 201; vol. xxiv. XXIII, On the Compounds of Ethylene-sodium and of its Homologues. By J. ALFRED WANKLYN, Professor of Chemistry in the London Institution*. THE reaction described at the end of my former paper indicates very distinctly that the absolute ethylate of sodium got by heating the well-known crystals is in reality hydrated oxide of ethylene-sodium, the substances arising from the action of the ethers on this compound being the different salts of the new organo-metal ethylene-sodium. ((C2 H4)" Na")'=Ethylene-sodium (radical). (C2 H4 Na)' HO-Hydrated oxide of ethylene-sodium. (C2H4 Na) C2 H3 O (C2 H4 Na)' O=Acetate of ethylene-sodium. C5 H900=Valerianate of ethylene-sodium. (C2 H4 Na)}O=Benzoate of ethylene-sodium. C7 ((C5 H10)" Na"")'= Amylene-sodium (radical). (C3 H1o Na)' } O=Hydrated oxide of amylene-sodium. H (C5 H10 Na)' C2 H3 OS C5 H10 Na C5 H9 O O-Acetate of amylene-sodium. O=Valerianate of amylene-sodium. The foregoing is a list of the formulæ of such compounds of ethylene-sodium and of amylene-sodium as have been already produced, to which are added the formulæ of the radicals themselves. Ethylene-sodium and Amylene-sodium (radicals). It will of course be understood that should these radicals be capable of existing in an isolated state, their formulæ in that state must be double of that which represents them in a state of combination. Thus we should have: (C2 H4 Na)' (C2 H4 Na)' free ethylene-sodium. Very great difficulties will have to be overcome before the free radicals can be actually prepared. Passing in review the history of the isolation of the organo-metallic radicals, it will be Communicated by the Author. Phil. Mag. vol. xxxvii. p. 117. * understood that the methods which have answered in the instances already known are not likely to answer in the present case. Kakodyle was obtained from chloride of kakodyle by driving out kakodyle by means of zinc. Supposing, however, that I had got the chloride of ethylene-sodium, what metal could I expect to be capable of driving out ethylene-sodium? Zincethyle was obtained by the distillation of the double zinccompound of iodine and ethyle, when, as is well-known, zincethyle distils over. The non-volatility of ethylene-sodium is a bar to the establishment of a parallel process. The only hope which I have at present of isolating the new radical is the hope of finding it among the products of the destructive distillation of the double compound of sodium-ethyle and zinc-ethyle, not, however, in the distillate, but in the residue, along with the finely divided zinc and sodium which results from the destructive distillation in question. With respect to the chemical constitution of ethylene-sodium, there are two modes of representation which will commend themselves to the chemical mind, viz. : ((C2 H4)" Na')', and ((C2 H4)" Na"")'. Against the first, and in favour of the second formula (that to which I have given the preference) may be urged the fact that sodium appears to be a trivalent metal; and also that the first method of representation would necessitate the assumption that in the hydrated oxide there existed oxygen not in direct union with sodium, whilst the second formula represents the sodium as directly combined with oxygen. Another reason for giving the preference to the second formula will be mentioned on a future occasion. In support of the statement that sodium is a tri-valent metal, a statement which will be looked upon as a chemical heresy in certain quarters, I would bring forward the cases of the double zinc-sodium-ethyle and of sodium-triacetyle. The analysis of the first of these compounds led to the empirical formula (Na C2 H3+Zn (C2 H5)2), as will be seen on reference to my paper on the subject. It will also be remembered that I altogether failed to effect a separation between the sodium-ethyle and the zinc-ethyle. The real constitution of the compound is : Na""-C2 H5 C2 H5 * Na=23, Zn=65. Sodium-triacetyle, as I pointed out at the last Meeting of the British Association (vide also the January Number of Liebig's Annalen), is obtained by the action of sodium on acetic ether. Although its formula may be represented in another way, still the most elegant representation is Na"" (C2 H3 Oj3. In the common sodium-salts I regard the sodium as having united with itself; thus common salt is looked upon as being Na""-Cl Na"-Cl In fine, I regard sodium as being an analogue of nitrogen and arsenic rather than of hydrogen. Hydrated Oxide of Ethylene-sodium. This compound was described in my last paper under the name of the absolute ethylate of sodium, and is obtained by heating the well-known crystals which are the product of the action of sodium on alcohol. It is also formed by the action of sodium on the ethyle-ethers of the fatty acids. It is a snow-white amorphous solid, non-fusible, and of remarkably low specific gravity. There are difficulties in the way of taking its specific gravity with great precision. It appears to be lighter than ether, in which it swims. There is just the possibility that this extreme lowness of specific gravity may be to some extent simulated, and that the floating in ether may be due to adherent gas (hydrogen). Whether or not the specific gravity is lower than that of ether must be determined by further experiment; but that the specific gravity does not exceed that of water has been shown by a determination. As has already been described, this substance possesses the property of withstanding a very high temperature without decomposition. It will bear being heated to 290° C.; possibly it will bear a much higher temperature; but, as might have been expected, it will not bear a low red heat without carbonizing." In contact with excess of water, it gives caustic soda and alcohol, the latter, as I showed in my last paper, being obtained in the theoretical quantity from product which had undergone heating to 200° C. Heated with an insufficient quantity of water to convert all of it into caustic soda and alcohol, the reaction is still of the same kind, a quantity of water liberating an equivalent of alcohol, thus: 2. C2 H4 Na · -O +2 H2 O = 2C2 Ho O +Na2 (HO)2. Phil. Mag. S. 4. Vol. 37. No. 248. Mar. 1869. N |