102 



CHEMISTRY. 



tion, while depolymerization is a homogeneous 

 disintegration. These two forms of the chemi- 

 cal process are respectively metamorphosis by 

 condensation and by expansion. As between 

 unlike species they constitute heterogeneous 

 integration and heterogeneous disintegration, 

 or chemical metagenesis, and give rise to 

 species differing in centesimal composition 

 from the parents. The chemical species to 

 those agencies which do not effect its disinte- 

 gration, is a complete entity or integer. This, 

 in the case of homogeneous integration of gases 

 and vapors, is generated by the condensation 

 into a single volume of two or more volumes 

 of less condensed species ; as where the atoms 

 H + H became the molecule IP. A number 

 of substances are named which are double or 

 dyad integers at normal temperatures, while 

 others, tryad, tetrad, hexad, etc., at ordinary 

 temperatures become dissociated by intense 

 heating into equivalent numbers of dyads. As 

 the specific gravity is known to vary with 

 the equivalent weight in the case of gases and 

 vapors, so a similar direct relation is indicated 

 in liquids and in solids ; and the hardness and 

 chemical indifference of solid species are in like 

 manner functions of their atomic weights. 

 Further, the author advances that the gas or 

 vapor of a volatile body constitutes a species 

 distinct from the same body in its liquid or 

 solid state, the chemical formula of the latter 

 being some multiple of the first; and the liquid 

 and solid species (probably al ways) constitute 

 two distinct species of different atomic weights, 

 whence it follows that all condensation of gases 

 and vapors by cold or pressure, and all fusion, 

 solidification, and vaporization, are chemical 

 metamorphoses. This is in accordance with 

 Henri Sainte-Claire Deville's views on disso- 

 ciation. It is also in harmony with a sugges- 

 tion by Prof. J. P. Cooke, that certain alloys 

 are to be regarded in part as examples of a 

 progressive series of isomorphous compounds of 

 antimony and zinc of high equivalent, differing 

 from each other nZn a . This term is not to be 

 considered a deviation from the law of definite 

 proportions, but " only an expression of that 

 law in a higher form." 



Chemical Physics. In his report on the subject 

 of solution made to the meeting of the British 

 Association, in 1885, Prof. W. A. Tilden particu- 

 larly referred to the question whether the phe- 

 nomena of that name are to be considered 

 chemical or mechanical. At what point in the 

 curve of the evolution of heat which takes 

 place during the process of solution can we set 

 up a distinction between the effect due to 

 chemical combination and that due to other 

 causes, such as the change of volume conse- 

 quent on dilution, or the possible loss of energy 

 from the adjustment of the motion of the mole- 

 cules of the constituents to the conditions req- 

 uisite for the formation of a homogeneous liq- 

 uid, or the decomposition of the compound by 

 the water? In the action of the solution of 

 solids in water, the volume of the solution is 



always, with the exception of some ammoni- 

 um salts, less than the sum of the volumes of 

 the solid and its solvent. Similarly, the ad- 

 dition of water to a solution is followed by 

 contraction, which may be due to mechanical 

 fitting of the molecules of the one liquid into 

 the interspaces between those of the other ; or 

 to a readjustment of molecular motion. The 

 heat evolved or absorbed during the admixture 

 of any substance with water is a continuous 

 function of the quantity of water added. Simi- 

 larly, the contraction which ensues on diluting 

 an aqueous solution proceeds continuously, and 

 the molecular volume of a salt in solutions of 

 different strengths is continuously greater the 

 larger the amount of salt present. So that no 

 indication is observed of the formation of com- 

 pounds of definite composition distinguishable 

 by characteristic properties. As to the question 

 whether the solvent and the substance dissolved 

 in it, or any portion thereof, exist independently 

 of one another the view seems preferable that 

 save, perhaps,in excessively dilute solutions, the 

 dissolved substance is attached in some way 

 to the whole of the water. As to what deter- 

 mines the solubility of a substance, the follow- 

 ing propositions seem to be true : Nearly all 

 salts which contain water of crystallization are 

 soluble in water, and for the most part easily 

 soluble ; insoluble salts are almost always des- 

 titute of water of crystallization, and rarely con- 

 tain the elements of water. In a series of salts 

 containing nearly allied metals, the solubility 

 and capacity for uniting with water of crystal- 

 lization generally diminish as the atomic weight 

 increases. The fusibility of a substance has 

 much to do with its solubility. Neither fusi- 

 bility alone nor chemical constitution alone 

 seems sufficient to determine whether a solid 

 shall be soluble or not, but it may be taken as 

 a rule that when there is a close connection 

 in chemical constitution between a liquid and a 

 solid, and the solid is at the same time easily 

 fusible, it will also be easily soluble in that 

 liquid. Salts containing water of crystalliza- 

 tion may be considered as closely resembling 

 water itself, and these are, for the most part, 

 both easily fusible and easily soluble in water. 

 No definite explanation of supersaturation has 

 been generally accepted. In the opinion 

 of the speaker it is identical with superfusion. 

 The conclusion seems inevitable that chemical 

 combination is not to be distinguished by any 

 absolute criterion from mere physical or me- 

 chanical aggregation; and probably chemical 

 combination differs from mechanical combina- 

 tion called cohesion or adhesion chiefly in 

 the fact that the atoms or molecules of the 

 bodies concerned come relatively closer togeth- 

 er, and the consequent loss of energy is greater. 

 From experiments on more than forty ele- 

 ments, Mr. James Blake supposes that the action 

 of inorganic substances upon living matter de- 

 pends on their isomorphic relations, and that 

 all substances belonging to one and the same 

 isomorphous group give rise approximately tc 



