﻿166 Mr. C. Tomlinsorr's Historical Notes on some 



la fois et de la propriete conductive pour le calorique et du poli 

 des surfaces/'' When a flask half full of water is in a state of 

 ebullition, a peculiar noise shows that the boiling goes on with 

 difficulty; large bubbles of steam proceed from certain points 

 only of the surface, and a thermometer plunged into the water 

 shows frequent variations. In a tinned-iron vessel, on the con- 

 trary, the bubbles of steam are not so large, but they are more 

 numerous, the variations of the thermometer are less consider- 

 able, and the boiling point is not so high. If, however, water 

 be boiled in a glass vessel and a few pinches of iron-filings be put 

 into the vessel, the boiling instantly goes on as in a metal vessel. 

 In the absence of this aid, the quantity of steam formed is pro- 

 portional to the excess of the temperature of the water over that 

 of its boiling-point. The temperature falls to 100° C. with a 

 sort of explosion, the steam having to overcome the cohesion of 

 the liquid and its resistance to change of state. This cohesion, 

 or viscosity of the liquid, must exert a great influence on its 

 boiling-point, since the steam has to overcome not only the 

 atmospheric pressure, but also the cohesion of the liquid mole- 

 cules. Then, again, the adhesion of the liquid to the vessel 

 must be a force analogous to its viscosity. The conducting- 

 power of the vessel for heat and the nature of its surface must 

 also exert considerable influence on the boiling-point of water. 

 Water boils more easily in a glass vessel into which powdered 

 glass has been thrown, than in a glass containing nothing but 

 water. 



9. Gay-Lussac illustrates the greater or less ease with which 

 steam escapes from boiling water by referring to the readiness 

 with which carbonic acid escapes from fermented liquors, such as 

 beer or champagne, especially when a bit of paper or a crust of 

 bread, &c, is introduced, or simply by stirring. Carbonic acid is 

 mostly disengaged from the sides of the vessel, and especially from 

 parts containing asperities. The bubbles increase in size in traver- 

 sing the liquid, because they establish in it a solution of continuity 

 which is very favourable to the disengagement of the gas. It is 

 easy to explain by these facts the phenomena of soubresauts or 

 "jumping ebullition," or "kicking-." When the liquid is above 

 the boiling-point, it is in a forced state; and in an instant a 

 burst of steam is formed, the liquid is thrown out, and the vessel 

 itself raised. This is especially the case in distilling sulphuric 

 acid ; but if some pieces of platinum wire be put into the retort, 

 the distillation then becomes easy. 



10. It is impossible to read this paper without being struck 

 with the large amount of suggestion contained in it. Indeed 

 Gay-Lussac's imagination was so lively that it seldom left him 

 satisfied with one explanation when he had to discuss some new 



