( 668 ) 



the wlieel until tho })()iiit of the triangulai' opening of the piece E 

 just reaches above the niercut-y. This will be observed at once as a 

 cnrrent of air and mercury then passes from B towards H. If for 

 some reason the division of air and mercnrv does not take place at 

 once, a tapping' of B is sufficient to etfect this. The mercurv which 

 is carried oxer, is thrown forcibly against the side of //, l)ut this 

 being constructed as a trap, no mercury can be carried over with 

 the escaping air through / or K. 



If the desired pressure is not yet attained, ^1 is turned lower or 

 higher, should the pressure be still too great or too small. But once 

 the required pressure attained, it will remani constant as air is 

 being continuously admitted through B. 



Suppose, for instance, that, owing to ijicipient decomposition, badly 

 condensable gases are formed dnring the distillation, the mercury 

 falls in ^1 ; the additional mercurv now arriving in the mercnrv 

 vessel renders the i)art of the /\ shaped o[)ening, which projected 

 above the mercury, smaller and in conseqnence less air can proceed 

 from B to H \ unless the powei- of the waterpnmp is exceeded the 

 original pressure will be maintained. If such is not the case the 

 original pressure must be again restored by nio\ ing A. 



Instead of the barometer and the manometer tube a shortened 

 j)ressure gange with movable scale (like the gauge of an airpnmp) 

 may be em[)loyed ^). 



Physics. — ''Methods and apparatus used in the cryogenic lahora- 

 tonj VI. TJte met hy /chloride circidation ." By Prof. H. Kamkr- 

 T,iNGH OxNES. (Comm. X". 87 from the physical Laboratory at 

 Leiden). 



(Communicated in the meeting of June 27, 1903). 



§ I. 71ie methi/Ichhride boiling vessel In Comm. N'^ 14 Dec. 

 '94 in the descri]>tion of the cascade of circulations which produces 

 the permanent bath of liqind oxygen for different measurements, I 

 have mentioned that the methylchloride refrigerator used there left 

 much to be desired. At the time when I arrajiged the cryogenic 

 laboratory at Leiden, the use of liquefied ethylene in a circulation 

 to obtain an efficient circulation of liquid oxygen was an untouched 

 scientific problem. As a result my attention was ju-incipally concen- 

 trated — besides on the question of obtaining a permanent bath of liquid 



1) The apparatus may be obtained from the Ned. Instrumenten Fabriek. Utrecht. 

 Holland. 



