308 Mr. G, Owen 07i Condensation Nuclei j^Toduced in 



The gas in the bulb thus suffers a sudden expansion. By 

 opening D the plunger will rise again to the same height. 

 The expansion can be increased by exhausting a little air out 

 of the bottle F through the tube E, the tap D being open at 

 the time. Smaller expansions can be obtained by allowing 

 some more gas to enter the apparatus through the U-tube S, 

 or (and this method was Aery often employed) by manipulating 

 the tap D so that the plunger does not ascend as far as it 

 would go. In the latter case, by noting the pressures of the 

 gas in the bulb before and after expanding, the value of the 

 expansion is easily calculated. 



If B be the height of the barometer, and tt the pressure of 

 water-vapour at the temperature of the experiment, then, 

 allowing the plunger to ascend as far as it will, the pressure 

 of the gas before expansion is 



Pl = B-,r, 



neglecting weight of plunger ; the pressure after expansion is 



P2 = B-7r-79, 



where p is the height of the mercury in the tube M above the 

 surface of the mercury in F. 



If vj = initial volume of the gas, and V2 = its final volume, 

 then the expansion is 



Vi ~ P2 ~ B — ir^p' 

 If the plunger be not allowed to rise as far as it would, and 

 pi = height of mercury in M before expanding 



i?2= 5 J ?5 



J7 



afte 



then ''? = PJ = |Z1^=&. 



Vi Fg B — TT— P2 



The U-tube S was used, as it afforded a very convenient 

 method of cutting off communication between the experi- 

 mental bulb and the atmosphere or the gas-generating 

 apparatus. 



To prevent the water-vapour condensing on the glass in 

 small drops, and so obstructing a clear view of the interior of 

 the cloud-chamber, the latter, after the insertion of the wire 

 in it, was well washed with nitric acid, or with chromic acid, 

 and then rinsed out with distilled water. This washino- 

 would also remove any dirt that might be on the wire. But 

 the latter was subjected to a further cleaning process by 

 being raised to a high temperature, yellow heat, for some 

 hours after the bulb had been fixed to the expansion apparatus. 



