1 66 



NATURE 



{Dec. 13, 1888 



temperature. Attention was directed to the difficulties students 

 generally experience on finding the dimensions of the same 

 electrical quantities to be difierent, according as they are ex- 

 pressed in electro-static or electro-magnetic measure, and that 

 different quantities may have the same dimensions. The ano- 

 malies are shown to be due to the suppression of the dimensions 

 of specific inductive capacity and permeability, each being called 

 unity in air. By retaining K and /« in the dimensional equations, 

 the author thinks that many difficulties will be avoided, the 

 methods of transformation of units will be generalized, and the 

 limits of our knowledge kept more clearly in view. Though 

 the dimensions of K and ^u cannot be determined, it is easily 

 shown that those of the product K^ i^ are L'^ T. Mr. Blakes- 

 ley, in commenting on thermal units, strongly protested against 

 the use of the word " therm " as a name for the unit of heat. 

 If used at all, it should be reserved for the unit of temperature. 

 Referring to the choice of fundamental units, he reminded the 

 Society that the dimensions of quantities expressed in the elec- 

 tro-static or electro-magnetic systems become identical if the 

 unit velocity be the velocity of light, and by choosing the unit 

 of time as a suitable decimal part of a day, the relations between 

 electrical and practical mechanical units could be simplified. Prof. 

 Carey Foster, after discussing the effect of defining specific heat 

 as a ratio, or as a quantity of heat as the dimensions of temper- 

 ature, pointed out that, as quantity of heat = temperature x 

 entropy, the dimensions of temperature would be determinate 

 if those of entropy were found. Prof. S. P. Thompson con- 

 sidered that part of the difficulties of dimensional equations arose 

 from the fact that no distinction was made between scalar and 

 vector quantities. Thus the dimensions of work and moment of 

 a force are given as ML-T"-, whereas the true representation 

 for the latter would be ML^T"- V— i, because the line by which 

 the force is multiplied is at right angles to the force. By similar con- 

 siderations, Ampere's rule for the force between two parallel current 



elements can be derived from the magnetic equation 



-f> 



for, replacing m and vt by equivalent current elements, i . ds and 

 i . ds\ the equation becomes — 



/ = 



i . ds . V ■ 



I i . ds 



i^ds . ds' 



Referring to the use of " therm," Dr. Thompson concurred with 

 the remarks of Mr. Blakesley, and thought the word "calorie" 

 answered all requirements. He also considered that thermal 

 equations were greatly simplified by always expressing specific 

 heat in ergs. Prof Ayrton was of opinion that students ex- 

 perienced much greater difficulty in dealing with electrical units 

 than with thermal ones, and thought part of this was due to the 

 vague way in which some of the standard text-books treated the 

 subject. With reference to the force exerted by quantities of 

 electricity. Prof. Perry and himself had pointed out that specific 

 inductive capacity must be taken into account, for, contrary to 

 Faraday, they had found it to be different in different gases. In 

 reply, Prof Riicker said he often explained the identity of the 

 dimensions of work and moment of a force, by considering 

 moment as measured by the work done in rotating through unit 

 angle, the dimensions of angle being zero as regards L, M, and 

 T. He also pointed out that, in Bayne's " Thermodynamics," 

 specific heats are always expressed in ergs. In thanking Prof. 

 Riicker for his interesting paper, the President expressed his 

 conviction that, by paying attention to the points considered, 

 the difficulties arising from the two systems of units would be 

 considerably diminished. 



Chemical Society, November 15. — Mr. W. Crookes, F.R.S., 

 in the chair. — The following papers were read : — The principles 

 of thermo-chemistry, by Mr. S. U. Pickering. The author 

 rejects the thermo-chemical principles enunciated by Thomsen, 

 Naumann, and Berthelot, not only on special grounds, but on 

 the more general ground that they depend on an impossible dis- 

 tinction between chemical and physical actions. A satisfactory 

 explanation of all known theraio-chemical facts is derived from the 

 recognirion of the laws of dissociation and the hydrate theory of 

 dissolution. Every act of combination must be accompanied by the 

 evolution of heat, and in interactions where heat is absorbed 

 this absorption must be due to the fact that, one or more of the 

 agents being partially dissociated at the temperature of the inter- 



action, the removal of one of the products of the dissociation 

 necessitates a further decomposition of the agent. The heat 

 evolved must also be a direct measure of the affinities saturated ; 

 and, of two possible interactions, that which evolves more heat 

 must occur to the exclu.sion of the other. The cases of endo- 

 thermic changes which present difficulties are those in which 

 liquids and solids are concerned. The heat absorbed when many 

 .colids are dissolved in liquids cannot be explained by the fusion, 

 but only by the volatilization of the solid. A mass of water 

 contains some fundamental molecules posjssinT an energy of 

 10,000 cal greater than the average molecular aggregates con- 

 stituting the mass. These can therefore combine with the salt, 

 and effect its volatilization with an evolution of heat, even if the 

 heat of volatilization be nearly 10,000 cal. ; other water aggre- 

 gates then dissociate to supply the place of the free molecules 

 thus removed from the sphere of action. From theoretical con- 

 siderations the author arrives at the conclusion that BerthoJlet's 

 theory as to the division of a base between two acids is correct, 

 and argues that the facts observed are in accordance with these 

 conclusions, and are entirely opposed to the existence of the 

 so-called "avidity" or "affinity" constants advocated by 

 Ostwald and others. In the discussion which followed the 

 reading of the paper. Prof. Ramsay. F.R.S., said that he did not 

 believe in the universal presence of cojiplex molecules in liquids 

 and solids, nor did he exclude the existence of such ; the re- 

 searches of Prof. Young and himself, he thought, conclusively 

 established the absence of a complex molecular structure in such 

 liquids as ethyl alcohol and ether, whilst, on the other hand, 

 Henry's arguments testified to the complexity of the molecules of 

 certain oxides, such as silica. With regard to water, which 

 specially formed the subject of Mr. Pickering's remarks, it was 

 to be noted that, whilst the vapour-density pointed to molecular 

 simplicity, other arguments drawn from its behaviour when 

 examined by Raoult's method were in favour of moderate mole- 

 cular complexity. Prof. Armstrong, F.R. S., remarked that by 

 taking into account the action of water, Mr. Pickering had ad- 

 vanced what appeared to be a rational explanation of many facts 

 which hitherto had appeared paradoxical. — Note on the mixture 

 of propyl alcohol and water, by Prof. Ramsay, F. R, S., and 

 Prof. Young. The authors have determined the vapour-pressures 

 of a' mixture of propyl alcohol and water in the proportions 

 CsHgO : HgO, and like Konowalow, arrive at results adverse to 

 the conclusion that a definite hydrate exists. Chancel found 

 that this mixture distils over to the last drop at 87°"5 under 

 738 mm. pressure, but the authors find that the composition of 

 the mixture of constant boiling-point varies with the pressure 

 under which distillation takes place. — Note on the action of 

 nitric acid on ammonium chloride, by Dr. F. E. Matthews. 

 The principal gaseous product' of the action of nitric acid on 

 ammonium chloride in solution is nitrous oxide, and not nitrogen, 

 as has been previously stated ; the gas is mixed with small quan- 

 tities of chlorine and oxychloride of nitrogen. — Ethylic cinnamyl- 

 diethacetate, by the same. — The isomeric sulphonic acids of 

 i3-naphthylamine, by Mr. A. G. Green. Three acids — the a-, 

 j3-, and 7-acids — are known to be formed when yS-naphthylamine 

 is sulphonated with ordinary sulphuric acid at 100°, but the 

 author finds, as was to be expected, that the 8-acid is also 

 present. The analogous behaviour of hydroxy- and amido-com- 

 pounds makes it probable that ^-naphthol on sulphonation gives 

 four isomeric sulphonic acids, although two only have hitherto 

 been isolated, and the author's experiments confirm this view, inas- 

 much as he has succeeded in isolating a third acid — corresponding 

 to the )8-naphthylamine-5-sulphonic acid— from the product 

 formed on sulphonating /8-naphthol at 100°. In the discussion 

 which followed, Prof. Armstrong, F.R.S., and Mr. W^ynne 

 pointed out that the formula adopted by Mr. Green as repre- 

 senting the constitution of the /8-naphthylamine-o-sulphonic acid 

 was at variance with the views put forward by Cleve and others, 

 and could not be accepted ; Mr. Green, in reply, defending his 

 view that the o-acidis an ortho-compound, mainly on the ground 

 that it and the corresponding fl-naphtholsulphonic acid differed 

 so greatly in properties from their isomerides. — The constitution 

 of the dichloronaphthalenes, especially the a;8-com pounds, by 

 Prof. Armstrong, F.R.S., and Mr. W. P. Wynne. The three 

 possible oa- and the two possible heteronucleal )33 dichloro- 

 naphthalenes are known, and formulas have been ascribed to 

 them which almost certainly are correct expressions of their 

 constitutions. The authors point out that the four possible 

 oj8-dichloronaphthalenes are also known, and draw attention to 

 the somewhat discrepant statements on record relating to the so- 



