446 Mr. C. Tomlinson on some Phenomena 



flask, it could be easily arranged with the mouth downwards or 

 upwards. A globular flask containing above ten ounces of di- 

 stilled water was employed. When the mouth of the small tube 

 was downwards the phenomena were much the same as before, 

 only the tube did not rest on the bottom unless held there. On 

 removing the lamp, the tube rapidly filled and sank with its 

 mouth upon the heated bottom, which expanding the enclosed 

 vapour caused it to disgorge the water and so to rise again. It 

 did this two or three times ; it then settled and filled ; but there 

 remained a small bead of air about the size of the head 

 of a small pin. On again applying the lamp, the water boiled 

 readily; but 75 seconds elapsed before the tube became active; 

 and it was not until bubbles of vapour passed up into it and 

 displaced the water that the tube was in a condition to pour out 

 its intermittent bubbles ; and it seems to me of importance to 

 insist on this point, namely that on this as on many other 

 occasions the flask boiled, so to speak, from its own independent 

 resources, long before the little bell or the small tube came into 

 action at all; and when either of them did so it behaved simply 

 as a nucleus, increasing the amount of vapour that was given off 

 by the boiling liquid. The flask boiled first from the action of 

 the heated bottom and the presence of minute specks, probably 

 of carbon, on the surface of the bottom, the importance of which 

 I insisted on in my first paper. The air in the bell or in the 

 small tube was displaced by expansion; and if at length the 

 whole of the air was not got rid of, the reason seems to be the 

 impossibility of doing so by expansion, just as it is impossible to 

 obtain a perfect vacuum in the receiver of an ordinary air-pump. 

 The air in the receiver goes on expanding until an exceedingly 

 thin medium is left ; and the air in the tube in boiling water is 

 pumped out by expansion, and the minute portion that at length 

 remains shows, not that this speck is necessary to carry on the 

 ebullition, but simply that it is impossible to exhaust the tube by 

 expansion only. Hence I see no reason to qualify the statement 

 made in my first paper, namely that I cannot help thinking 

 that too much importance has been attached to this small 

 residual speck of air in the phenomena of boiling liquids. If a 

 speck of air be thus left in the tube, a minute portion also pro- 

 bably exists in other parts of the liquid, although I have failed 

 to detect it. Moreover by repeatedly boiling the flask at intervals 

 of five or ten minutes, and allowing the small tube to fill after each 

 boiling, the water becomes so far purged of air that the speck in 

 the tube disappears, or is so minute that I have been unable to 

 pronounce as to its existence. Of course it may have entered 

 into solution even during the observation. 



In some of the low-boiling liquids the speck rapidly dimi- 



