58 M. W. Feddersen on Thermo diffusion of Gases. 



In this example, therefore, between 9 h 25 m and 9 h 35 m the 

 oil drop on the hot side removed 190 millims. from the heated 

 part; while that on the cold side moved 155 millims. nearer 

 to the cold end of the palladium. 



Gypsum. — In a tube of 12J millims. internal diameter was a 

 plug of gypsum 70 millims. in length, which, after its pouring- 

 in, had remained some time and become air-dry. The glass 

 tube was encased in sheet copper over one end of the plug; and 

 by a feebly burning spirit-lamp placed beneath, that part was 

 heated to about 200°*, while it was protected from draughts as 

 much as possible by pasteboard walls. The other end of the 

 plug was exposed to the temperature of the room (8°), and mani- 

 fested, when touched, a very slight warming. On stopping the 

 accessory tubes, 3J millims. in diameter, with mercury, no 

 movement made its appearance even after fifteen hours. When 

 afterwards sulphuric hydrate was taken for the liquid stop, I ob- 

 tained the following displacements in the direction from the cold 

 to the hot side : — 



Time. 



Cold side. 



Hot side. 



Observed. 



Calculated for 

 10 minutes. 



Observed. 



Calculated for 

 10 minutes. 



h m h m 

 10 15 to 10 45 



10 45 „ 11 30 



11 30 „ 12 15 



12 15 „ 1 15 

 1 30 „ 2 



millims. 

 tube wanting. 



52 

 52 

 20 



millims. 



i'i : 5' 



87 

 6-7 



millims. 

 60 

 87 

 45 

 32 

 23 



millims. 

 200 

 19-3 

 100 



5 3 



7-7 



The aqueous vapour developed from the gypsum, at first in 

 large quantity, and at last only sparingly, did not disturb the 

 direction of the phenomenon. 



Charcoal. — Instead of gypsum the tube had, under otherwise 

 like conditions, a plug, 90 millims. in length, of coarsely pow- 

 dered and recently heated fir charcoal. After the setting-up 

 the drop of sulphuric acid did not at first move at all on the 

 heated side, while on the cold side it moved briskly toward the 

 charcoal. 



* The temperature was measured, as the bulb of a thermometer rested 

 on the copper sheath ; above, it was somewhat protected from radiation by 

 a loose-lying piece of pasteboard. As is seen, the determination is very 

 closely approximative. The temperature, however, was preserved pretty 

 constant. 



