Moaal imtitution of CKreat 13ritain, 



WEEKLY EVENING MEETING, 



Friday, March 16, 1855. 



Sir Henry Holland, Bart. F.R.S. Vice-President, 

 in the Chair. 



Dr. AVm. Odling, F.C.S. 

 On the Constitution of the Hydro-carhons. 



Every chemical compound may be regarded in a great number of 

 different aspects. Each of the different theories that have been 

 propounded concerning the chemical constitution of bodies, is true 

 in reference to one particular aspect, — untrue in reference to all 

 others. Theories are of the highest service when they enable us 

 to look upon a larger number of bodies from a single point of 

 view, — of the highest detriment, when they prevent us from making 

 use of all other points of view. To regard a body, or a class of 

 bodies, exclusively in one aspect, or, in other words, to view all 

 compounds by the light of a single theory, is necessarily to neglect 

 a whole host of phenomena and relations. He has the most com- 

 plete knowledge of a compound, who is capable of changing his 

 position, and looking at the body from every possible point of view. 



The theory of compound radicals is of the utmost service in 

 enabling us to look upon a large class of bodies in one single aspect, 

 in affording us one of the best means of arrangement, comparison, 

 and explanation : but it has no pretensions whatever to represent the 

 entire and absolute truth with regard to the constitution of bodies ; 

 it simply exhibits them from one of many excellent points of view ; 

 it has reference less to the actual constitution of the bodies, than to 

 our particular mode of regarding them. 



In proportion to the complexity of the constitution of a body, so 

 is the number of aspects in which it may be regarded, so is the 

 number of rational theories that may be entertained concerning it. 

 All of these theories belong to the same order of truth : they differ 

 from one another only in their greater or less degree of generality. 

 The theory of the greatest generality most nearly approximates to 

 the representation of bodies, especially typical bodies, by empirical 

 formulae, as unitary molecules. 



Adopting the proportional numbers of Gerhardt, we represent 

 the two-volume molecules of muriatic acid, water, ammonia, and 

 coal-gas, by CIH, OH*, NH^, CH* respectively. In accordance 

 Vol. II.— (No. 21.) f 



