308 



Intelligence and Miscellaneous Articles. 



Parallactic Equality, subjects which are not sufficiently developed 

 in Astronomical treatises. The author clearly explains some points 

 in these lunar irregularities which the student may find a diffi- 

 culty in thoroughly understanding, and clears up some apparent 

 paradoxes with which the subject is beset. 



On the whole, this little work will be found of great assistance 

 to students of mathematical astronomy, and we can strongly 

 recommend it to their attention. J. E. Gore. 



XXXI. Intelligence and Miscellaneous Articles. 



AN EXPERIMENT WITH SOLID CARBONIC ACID. 

 BY PROF. K. PRYTZ. 



INCITED by the interesting account by Prof. Bleekrode (Phil. 

 Mag. xxxviii. pp. 81-89, 1894) of his experiments with solid 

 carbonic acid, I wish to describe an experiment which I have made. 

 A quantity of solid carbonic acid being compressed in a wooden 

 cylinder, I cut the block of the substance in pieces small enough 

 to be put into a stout glass tube r 1*5 centim. wide. 

 When the tube was filled with the pieces of carbonic 

 acid, it was connected with a manometer M, the 

 cock h being open. On closing the cock the index 

 of the manometer rises slowly until the pressure is 

 as much as 5 atm. The index then stands completely 

 still for a tolerably long time ; at the same time we 

 see pieces of carbonic acid sink down on melting : 

 only when the whole is melted, and consequently 

 fills the bottom of the tube, does the index suddenly 

 rise again, and now much faster than before. 



When the index has reached 10 atm. the cock is 

 opened a little : the melted carbonic acid then 

 evaporates quickly, the pressure diminishes, the index 

 goes back to 5 atm. : there it suddenly stops again, 

 and is stationary until the carbonic acid is again 

 solid, whereupon it slowly goes back to 1 atm. 



The experiment is very instructive. It shows better than any 

 other that I know of the fixity and the identity of the melting 

 and solidifying points : it shows that solid carbonic acid only 

 melts under pressure, and it indicates the great difference between 

 the solid and the liquid carbonic acid in respect of conductivity 

 for heat. 



I usually place the glass tube in water ; the transparent ice 

 crust then formed shows the cold inside the tube. 



The Physical Laboratory of the 



Polytecknieal School at Copenhagen. 



KJ 



