32 I Intelligence and Miscellaneous Articles. 



with fragments of New Red Sandstone and nodular masses of 

 Dolomite. 



The author concludes by describing the mode of occurrence, in 

 the valley of the Derwent, of a marine deposit which he considers of 

 Postpliocene age, and which is found at an elevation of upwards of 

 100 ft. above the sea-level, and at a distance of from 50 to 100 

 yards from the water's edge — thus showing that the valley of the 

 Derwent and the neighbouring country had been recently upheaved. 



XXXVIII. Intelligence and Miscellaneous Articles. 



ON THE EBULLITION OF WATER, AND ON THE EXPLOSION OF 

 STEAM-BOILERS. BY M. L. DUFOUR. 



GASES, it is known, tend eminently to promote the vaporization 

 of liquids with which they are in contact. But the superficial 

 gaseous layer which adheres to solids, acting at first like gases 

 themselves, is gradually removed by prolonged and successive heat- 

 ing. When the solid surfaces are deprived of it, they no longer by 

 their contact excite changes of condition, but become indifferent in 

 the liquid. 



What confirms this view is the circumstance that, by maintain- 

 ing or producing on the surface of bodies a gaseous layer, ebullition 

 of a liquid is immediately produced if the temperature is suitable, 

 and any retardation of ebullition is avoided. The following experi- 

 ment realizes these conditions. Two platinum wires, communica- 

 ting with the outside, pass through a cork in which a thermometer 

 fits, and dip in water. They are connected with the two poles of a 

 galvanic element, and a slight disengagement of gas, due to electro- 

 lysis, takes place on their surface. Under these circumstances, and 

 so long as the current passes, it is impossible to obtain the least 

 retardation of boiling. If these wires cease to be connected with a 

 battery, after some successive heatings and by diminishing the super- 

 ficial pressure, retardations are produced similar to those mentioned 

 above. If the current is then made to pass, ebullition is imme- 

 diately produced. If the retardation is considerable (from 15 to 20 

 degrees), closing the circuit produces so abundant a production of 

 vapour as to resemble a true explosion. The vapour appears to 

 break away with an effort from the liquid mass, and the vessel experi- 

 ences concussions almost strong enough to break it. This experiment, 

 which has frequently succeeded in my hands with ordinary water, is 

 more striking in the case of slightly acidulated water, for then the 

 retardations are more pronounced. 



It is therefore, I think, a property of water to tend in most cases 

 to retain the liquid state, even when ebullition ought to take place, 

 provided the boiling-point has been reached by a diminution of the 

 superficial pressure after the liquid has been already heated, and after 

 it has been in contact for some time with the solid substances of the 

 vessel. This property is perhaps not without interest in its applica- 

 tion to the explosions of steam-boilers. This formidable phenome- 

 non is still enveloped in much obscurity. Various attempts have 



