250 Mr. C. Tomlinson on the Action of Solid Nuclei [Jan. 21, 



far above the surface. As in the case of charcoal and coke, the liberation 

 of vapour is confined to the solid nucleus, no part of the flask giving off 

 visible vapour. The following data show the influence of the solid upon the 

 temperature. Five ounces of distilled water in a clean flask boiled at 213^-g . 

 A small lump of platinum sponge was held in the flame of a spirit-lamp and 

 then put into the flask. The temperature subsided to 212^-°, and re- 

 mained so for some time. A second small piece of sponge was similarly 

 heated and put into the flask ; it was as active as the former piece in libe- 

 rating vapour, but there was no further depression of temperature. The 

 water was now allowed to get cold ; and on again applying the spirit-lamp 

 there was a good deal of loud explosive bumping, until the water was near 

 200°, when the platinum sponge began to give off steam and the boiling be- 

 came soft and regular. 



I have not the command of apparatus for determining the volume of 

 vapour absorbed by platinum sponge, charcoal, &c. at given temperatures ; 

 but it would not be difficult to do so by one or other of the contrivances 

 made by Dalton and Gay-Lussac in determining the elasticity of the va- 

 pours of liquids at the boiling-point. It would also be interesting to study 

 the action of nuclei on liquids heated above the pressure of one atmosphere. . 



Meerschaum is also an active nucleus. A bit of this substance was thrown 

 into a tube filled about one-third with newly distilled oil of turpentine 

 which boiled at about 310°. The whole tube became filled with bubbles; 

 and long after the lamp was removed the nucleus continued to liberate nu- 

 merous streams of bubbles, an effect that is common to all porous bodies 

 tried in these experiments, but more remarkable in some cases than 

 others*. 



A fine-grained pumice-stone cleaned in nitric acid, and another piece not 

 cleaned, were both very active in giving off vapour from liquids. As in the . 

 case of charcoal and meerschaum, they soon sank to the bottom of the ves- 

 sel, unless buoyed up by the steam while the lamp was burning under the 

 flask, and continued to pour off vapour so long as the liquid was at or near 

 the boiling-point. When the water was below 100°, the flask was put under 

 the receiver of an air-pump and the air exhausted ; the water soon boiled, 

 and the pumice was as active as before in liberating vapour. 



Chalk, plumbago, and platinum balls are all active promoters of vapori- 

 zation. 



In the absorption of gases by charcoal, Saussure found that, if a piece of 

 charcoal impregnated with one gas were introduced into another gas, a por- 



* Illustrations were frequently afforded in these experiments of the different action 

 of a clean as compared with an unclean surface. In the experiment in hand, in order 

 to take the temperature of the boiling turpentine, the thermometer-bulb and part of the 

 stem were made chemically clean ; but having on one occasion to leave the thermometer 

 in the tube, its bulb was made to rest on the bottom, so that about an inch and a half 

 of the stem that had not been made chemically clean became immersed. This portion 

 was instantly covered with minute beads of vapour, so as t o give it a frosted appearance, 

 exactly distinguishing the clean from the unclean portion. 



