Chemical Science. 201 



degree. One gas only forms an exception to the above statement, 

 namely, hydrogen, which was always heated more than the others, 

 namely, to 6.6 degrees in the five minutes. This effect is con- 

 sidered as due not to any difference in specific he*ti ]Mit»t4^)ia differ- 

 ence in conducting power. '■, <■')[■ .,',<\ pijd 71 



Experiments were then made with dilated gase& to ascertain 

 whether dilatation caused any change in capacity, and it was found 

 to diminish slowly but regularly with the diminution of pressure. 

 These results, with a third which is also interesting, have been thus 

 generally expressed by the authors at the end of their memoir. 



i. All gases in equal volumes, and at the same pressure, have 

 the same specific heat. 



ii. Other circumstances being the same, the specific heat of gases 

 diminishes with diminution of pressure, and equally for all the 

 gases : the progression converges slightly and in a ratio much less 

 than that of the pressures. 



iii. Each gas has a different conducting power, i.e., all the gases 

 have not the same power of communicating or receiving heat. — 

 Ann. de Chimie, xxxv. b» ,j.. -. .<!., 



2. On the Incandescence and Light of Lime. — The* experiments 

 made by Lieutenant Drummond upon the light of lime and other 

 earths when highly ignited, with the highly interesting application 

 which he has made of that emitted from lime, to the purpose of 

 geodesical surveys, has induced M. Pleischel to repeat and vary the 

 results. He states that the utmost light is given by lime; the earth 

 being pulverised and exposed on burning charcoal to the heat ex- 

 cited by a jet of oxygen falling upon it. He endeavours to account 

 for the effect, by supposing a kind of pulverulent atmosphere disen- 

 gaged from the lime at the high temperature used, and considers 

 that the substances which are competent to emit molecules only in 

 the gaseous state, cannot produce this intense ligli^^^—^^fil^hrift 

 far Physik, &c. ,,4^. . ^j^ lo siiH^.^.^ ' 



3. Evolution of Heat during the Compression of Water. May 

 14, 1827. — M. Arago announced to the Academy of Sciences, that 

 M. Despretz had ascertained experimentally, that the compression 

 of water by a force equal to 20 atmospheres, caused the disengage- 

 ment of one sixty-sixth part of a degree of heat. 



4. On Electrical Excitation. — M, Walcker affirms positively from 

 experiments made with great care, that three bodies of different 

 exciting power are necessary in every case of excitation of electri'^ 

 city by contact, and that all the phenomena of this kind are subject 

 to this condition. If, for instance, two portions of the same metal 

 being put in contact, electricity is produced, it is because there are 

 three different states of temperature brought into play, one being 

 the result of the other two, and a mean between them. One fact 

 which more than any other sanctioned this idea, was, that the elec- 



