CHEMISTRY. 



By H. Carkington Boi/ion, Pb. D., 



Professor of Clie'inislry, Trinity College, Hartford. 



GENERAL AND PHYSICAL. 



Present Aspects of the Theory of Chemical Action. — lu his presidential 

 address to the chemical sectiou of the British Association for the Ad- 

 vaucemeiit of Science, at the Aberdeen nieetinj^-, Prof. Henry E. Arm- 

 strong- considered, amonjj^ other things, the present aspects of the theory 

 of chemical action. He said : Chemical action may be defined as being 

 any action of wliich the conseqnence is an alteration in molecular con- 

 stitution or composition; the action may concern molecules which are 

 of only one kind — cases of mere decomposition, of isomeric change, and 

 of polymerization; or it may take place between dissimilar molecules 

 — cases of combination and of interchange. Hitherto it a])pears to 

 have been commonly assumed and almost universally taught by chemists 

 that action takes place directly between A and B, producing AB, or 

 between AB and CD, producing AC and BD, for example. This, at all 

 events, is the impression which the average student gains. Our text 

 books do not, in fact, as a rule deign to notice observations of such 

 fundamental importance as those of De La Eive on the behavior of 

 nearly pure zinc with dilute sulphuric acid, or the later ones of Faraday 

 {Ex2J. Researches, Series vii, 1834, 803 et seq.) on the insolubility of 

 amalgamated zinc in this acid. Belief in the equation Zn4-H2S04=^ 

 H2+ZnS04, hence, becomes a part of the chemist's creed, and it is 

 generally interpreted to mean that zinc will dissolve in suli)huric acid 

 forming zinc sulphate, not, as should be the case, that when zinc dis- 

 solves in sulphuric acid it produces zinc sulphate, &c. 



In studying the chemistry of carbon compounds we become ac- 

 quainted witli alarge number of instances in which a more or less minute 

 quantity of a substance is capable of inducing change in the body or 

 bodies with which it is associated without apparently itself being altered. 

 The polymerization of a number of cyanogen compounds and of alde- 

 hydes, the ''condensation" of ketonic compounds and the hydrolysis of 

 carbohydrates are cases in point, l)ut so little has been done to ascertain 



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