434 ,' Messpf.^ Flayfair and Joule on 



tlie gaseous state, even at very high temperatures, the im- 

 portance of discovering the law which governs the volumes of 

 these forms of matter, has long been I'ecognised, and for some 

 time past lias much engaged the attention of philosophers. 

 '(i!(The first chemist who drew attention to this subject was 

 Dr. Thomson, who published a Table*, in the year 1831, of 

 the specific volumes of certain of the metals, obtained by di^ 

 viding their atomic weights by their specific gravities. In 

 this table a remarkable coincidence of volume is observed in 

 several of the metals most nearly allied in chemical characters. 



More recently the subject has been examined in detail by 

 Kopp, Schroder and Persoz, whose researches have thrown 

 considerable light on this obscure department of physics. :> 



Koppt drew attention to the circumstance, that in many 

 cases isomorphous bodies possess the same atomic volume, 

 the law being correct when the isomorphism is strictly accu- 

 rate, but approximating only when this is not the case. He 

 admits also that perfect equality of the volume exists only at 

 particular temperatures, on account of the unequal expansion 

 of isomorphous crystals. odi iA .riou 



Schroder J made the interesting observation, that tire re- 

 mainder is the same when the primitive volume of the corre- 

 sponding member of a series of analogous compounds is sub- 

 tracted from them ; thus AO, BO and CO leave a constant 

 remainder when the known volumes of A, B and C are sub- 

 tracted respectively froHj the known atomic volume^ of the 

 compounds. .;^ oi!j ; • > doii') fli 



Kopp§ confirms this disdovery to a certain extent, belie- 

 ving, however, that the primitive volumes A, B and C must be 

 assumed in certain classes of salts to be different when in com- 

 bination with O from their volumes when isolated. He also 

 announces the discovery 1| of a great regularity in the })hysical 

 properties of analogous organic compounds, so much so, that 

 the study of the physical characters of the compounds of one 

 body enables us to predicate those of the corresponding com- 

 pounds of another substance. -^Z 



The discoveries of Schroder and Kopp, with regard to 

 ihe atomic volumes of liquid and solid bodies, do not, except 

 in a very kw instances, indicate an approach to a simple mul- 

 tiple ratio of volumes, and are therefore only in a small de- 



* Chemistry of Inorganic Bodies, vol. i. p. 14. sj' 



; lf Ppggendarff's 4\Wol^^t yflff^^l^"- > ""'^ Annnl^n c{cr Chevife, yo], xxxvi. 



X PoggendorfTs ^i^wwa/ew, vol. I. p. 554. 



§ Ueber das Spec'ifische Gewicht der Chemischen Verhindungen. Ifrank- 

 fort, 1841. 



II Annalen der Chemie, vol. xli. p. 79- 



