112 Dr. Carnelley on the Influence of Atomic Arrangement 



solidification supervened ; while the analogous structure de- 

 veloped by the desiccation of homogeneous masses of moist 

 clay, mud, or starch appears to be produced by a similar strain 

 consequent upon shrinkage from loss of moisture. In a 

 similar manner, the tense superficial capillary film of the 

 water, when it experiences the sudden molecular impulse due to 

 the emergence of the elastic pulse, is ruptured along lines more 

 or less symmetrically disposed on the surface of the water ; 

 and the* liquid beneath is projected through these lines or 

 points of least resistance. 



Berkeley, California, Oct. 25, 1881. 



XIII. Chemical Symmetry, or the Influence of Atomic Arrange- 

 ment on the Physical Properties of Compounds. By Thomas 

 Caenellet, D.Sc, Professor of Chemistry in Firth College, 

 Shefeld*. 



TWO years ago I published in this Magazine (Oct. 1879) 

 a paper on the Influence of Atomic Weight, in which 

 I endeavoured to trace the connexion between the atomic 

 weights of the elements and their properties and those of their 

 compounds. In the present paper I wish to consider this sub- 

 ject from a different point of view, viz. the influence which 

 the atomic position or arrangement has on the properties of 

 compounds. 



This is a subject which has lately absorbed a great deal of 

 attention, more especially as regards the connexion between 

 the refractive indices of compounds and the arrangement of 

 their constituent atoms in the molecule; and it will be my 

 object to give as brief and as clear a sketch as possible of the 

 chief results which have been obtained up to the present, tra- 

 cing the influence which atomic arrangement has on (1) the 

 melting-point, (2) the solubility, (3) the heat of formation, 

 (4) the heat of combustion, (5) the action of polarized light, 

 (6) the specific refraction, and (7) the tinctorial properties of 

 chemical compounds. For this purpose I shall necessarily 

 limit myself entirely to Ae consideration of carbon compounds, 

 and to those which are isomeric with one another. 



Those compounds are said to be isomeric which, though 

 having the same percentage composition and the same mole- 

 cular weight, have very different physical and chemical pro- 

 perties. This difference in properties must evidently depend 

 on the different arrangement or linking together of atoms in 

 the molecules of the several compounds. Thus, acetic acid 



* Communicated by tlie Author, being the Opening Address of the 

 Session to the Owens "College Chemical Society, Nov. 18, 1881. 



