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



began to seethe audibly, and it continued to give off vapour during more 

 than two minutes, the paper pellet resting during the latter part of the 

 time on the top of the cage. Similar good results were also obtained with 

 oil of turpentine. The cage was also lowered into naphtha, and some of 

 the other low boiling liquids, and whenever there was an escape of vapour, 

 it could always be referred to some unclean portion of the cage. Care is 

 required in lowering the cage, so as to expand trie air ; for unless this be 

 properly done, there may be a violent burst of air when the cage is near 

 the bottom of the tube. 



It really does seem to me that too much importance has been attached 

 to the presence of air and gases in water and other liquids as a necessary 

 condition of their boiling. Cold water dissolves only one-fiftieth of its 

 volume of nitrogen, and one twenty-fifth of its volume of oxygen, and these 

 small quantities must be reduced to an almost inappreciable amount in hot 

 or boiling water ; and yet some observers represent boiling water purged 

 of air as reabsorbing it eagerly while still boiling, The only function I 

 should assign to air would be that of diminishing somewhat the cohesive 

 force of the liquid molecules. If the tube be of narrow bore and chemi- 

 cally clean, or becomes so by the action of the liquid, adhesion has some 

 influence in raising the boiling-point. But the mode of heating the liquid 

 is of still greater importance in this respect, as is evident in De Luc's ex- 

 periments, and was well brought out in Bostock's. In the latter case 

 ether in a matrass over a spirit-lamp, boiled at 1 1 2°; but in a test-tube in hot 

 water at 150° and even 1 75° F. The difference in the conditions of heating 

 has doubtless been regarded as too evident to be insisted on ; and yet it is 

 of great importance in studying the conditions under which the boiling- 

 point of a liquid becomes raised. When the vessel is placed over a flame, 

 that part in contact with the flame is heated, or tends to become heated, 

 much more strongly than the rest of the vessel. This produces active 

 convective currents, the effect of which is to loosen the cohesion of the 

 particles, and so allow vapour to form more easily. When the water once 

 begins to assume the elastic form, it does so from the overheated part of the 

 vessel in contact with the flame. In a clean glass vessel containing distilled 

 water placed over a spirit-lamp, no air-bubbles form, either on the sides or on 

 the clean thermometer. They appear on the bottom surface only, playing 

 about and disappearing upwards until the water is at about 160°. At 

 about 180° small steam -bubbles are given off from the bottom heated sur- 

 face with a crackling noise ; they rise rapidly, expand, and disappear before 

 reaching the surface ; and until they succeed in doing so, the convective 

 currents are active. When the bubbles reach the surface and discharge 

 steam into the air, the whole column in broken up, cohesion is overcome, 

 and the boiling is maintained, while the liquid gradually disappears. Such 

 is the process of boiling in a vessel heated by a flame from below. When, 

 however, all that part of the vessel (such as a test-tube) that contains 

 liquid is put into a hot bath, the whole column is equably heated, or 



