Royal Institution. 231 



phenomenon was even more strikingly exhibited by pinching the 

 rushing stream with the finger and thumb, the heat resulting there- 

 from being insupportable. 



The varied effects thus exhibited in the "rapids" neutralize one 

 another at a short distance from the orifice, leaving however a small 

 cooling effect, to ascertain the law of which and its amount for 

 various gases, the present researches have principally been insti- 

 tuted. A plug of cotton wool was employed, for the purpose at once 

 of preventing the escape of thermal effect in the rapids, and of me- 

 chanical effect in the shape of sound. With this arrangement a 

 depression of o, 31 Cent, was observed, the temperature of the dry 

 atmospheric air in the receiver being 14°'5 Cent., and its pressure 

 34*4 lbs. on the square inch, and the pressure of the atmosphere 

 being 14*7 lbs. per square inch. 



ROYAL INSTITUTION OF GREAT BRITAIN. 



May 27, 1853. — "On the Formation of Hydrogen and its Ho- 

 mologues," by B. C. Brodie, Esq., F.R.S. 



In what is termed mineral chemistry, chemical substances are 

 classified according to the different nature of the elements of which 

 they consist. But in organic chemistry this distinction is no longer 

 available. Organic substances were formerly defined as triple com- 

 pounds of carbon, hydrogen and oxygen ; and this, with the state- 

 ment of the relative proportion of these elements in any given com- 

 pound, was all that was attempted to be made out as to its consti- 

 tution. But this class of bodies is more numerous possibly than all 

 the other chemical substances taken together with which we are 

 acquainted, and some further distinction was necessary for the pur- 

 poses of science. The sagacity of certain chemists at length disco- 

 vered a relation which was capable of becoming the basis of a truly 

 rational and natural classification. It was perceived, that in the 

 long series of chemical changes of which these bodies were suscep- 

 tible, the whole of the substance did not change, and that in these 

 combinations certain groups of elements had the same persistent 

 character and fulfilled the same chemical function as the simple 

 elements themselves in other bodies. These constant groups have 

 been named radicals. Among these, those hydrocarbons termed 

 the homologues of hydrogen are of special interest. TEthyle, a 

 group consisting of 2 atoms of carbon and 5 of hydrogen, C' 2 H 5 , is 

 one of these bodies. Assuming water as 2 atoms of hydrogen and 

 1 of oxygen, HHO, alcohol is composed of 1 atom of sethyle, 1 of 

 hydrogen, and 1 atom of oxygen, (C 2 H 5 ) HO. Hydriodic acid, 

 the iodide of hydrogen, consists of an atom of hydrogen combined 

 with an atom of iodine, HI. The iodide of sethyle consists of an 

 atom of sethyle combined with an atom of iodine, (C 2 H 5 )I. It is 

 from these, and other like analogies between hydrogen and aethyle, 

 that the idea arose of the similarity in their chemical function. 



Certain chemists, however, conceived these views to be mere fan- 



