Regulariti) in the Properties of analogous Compoimds. 187 



billing wilh another in several proportions, does not always 

 retain the same atomic volume, although these cases appear 

 to be of less frequent occurrence than those in which it always 

 retains one and the same atomic volume. 



The above is a short abstract of Dr. Kopp's most import- 

 ant researches on the specific weight of chemical compounds ; 

 at the same time he published another work on the specific 

 gravities of arbitrary mixtures, in which there are some im- 

 portant considerations with regard to the hydracid theory. 

 Should the above abstract meet with the favour of British 

 chemists, I may perhaps be induced to attempt something 

 similar with the last-mentioned work. 



January 11th, .1842. HenkY Croft. 



35 Upper Gower Street, London. 



XXVIII. On a great Regularity in the Physical Properties of 

 analogous Organic Compounds. By Dr. Hermann Kopp, 

 Lecturer at the University of Giessen*. 



TN a recent publication on the Specific Weights of Chemical 

 A Compounds f, I endeavoured to show how the atomic vo- 

 lumes of analogous groups of such combinations might be 

 very simply explained by means of certain general admissions, 

 and how the specific weight of any compound belonging to such 

 a group might be determined a priori with considerable ac- 

 curacy. This work was confined to inorganic compounds: I 

 have since then extended my researches to the organic com- 

 binations, and have likewise arrived at very simple results. 



In organic chemistry there are proportionally more liquid 

 compounds than in the inorganic, and the existence of dimor- 

 phism, which frequently renders the discovery of the laws for 

 the specific weight difficult in this latter branch, is of rarer 

 occurrence. The determinations of the densities of fluids are 

 in general easier, and the statements respecting them more 

 accurate than is the case with solid bodies. On the other 

 hand, fluids have a greater expansibility by heat than solids, 

 and as long as it remains unascertained at what temperature 

 a comparison of the specific volumes of various bodies can 

 properly be made, this stronger expansibility, which varies in 

 different compounds, appears to lay great difficulties in the 

 way of our aniving at correct results from a comparison of 

 s})ecific volumes. 1 have not hitherto been able to devote 

 any special attention to this subject, on account of the several 



• Communicated liy the Author. 



t Vide preceding abstract by Mr. H. Croft. 



