EECEXT PEOGRESS IN RELATIOX TO THE THEORY OF HEAT. 239 



of a pound of water. This datum of experiment serves as a basis for all caleula- 

 tions relating to the mechanical fheon/ of heat. 



Here, tben, there is a source of heat whose importance cannot escape our 

 attention. Consider the innumerable falls of water which exist upon the earth, 

 the waves of the ocean which resemble immense cataracts, incessantly renewed, 

 and if we would represent to ourselves the (Miornious (]Tiantity of heat they prct- 

 duce, take as an example the falls of the Rhine at Schaffhausen. It has been 

 calculated that this single water-fall creates in a day the heat required to melt 

 12,000 tons of ice. 



Nor is heat created by the impact of heavy bodies alone. When any force 

 has put a body in movement, it often happens that this movement is afterwards 

 annihilated, that is to say, it stops without being communicated to other bodies, 

 and heat becomes apparent. This is seen in the well-known experiment of the 

 fire syringe. ATe exert a muscular effort on a piston ; this compresses the air, 

 and our force seems fruitlessly expended. But if it is not employed in commu- 

 nicating motion, it serves to produce heat ; the compressed air is heated suffi- 

 ciently to kindle gun-cotton. We will lay it down then as a principle that heat 

 may arise from the destruction of movement. 



Our habitual sources of heat are chemical combinations. I take sulphuric 

 acid, diluted with Avater, in which I have immersed a small balloon containing 

 ether; I put zinc in this acid ; a lively chemical action is produced, and the mix- 

 ture is sufficiently heated to throw the ether into ebullition. The jet of vapor 

 rushes out by a slender tube, and may be made more conspicuous by kindling it. 

 The solution of zinc in an acid is therefore accompanied by a disengagement of 

 heat. 



The heat disengaged in a chemical reaction is often sufficiently intense to pro- 

 duce incandescence, and when the vivacity of action is very great, an explosion. 

 I shall cite some examples recently discovered, without going however into detail. 

 A leaf of paper is moistened with pyroligneous acid ; we touch it with a glass 

 rod coated withamixture of sulphuric acid and hypermanganate of potassium, and 

 the paper immediately takes fire. Again, we let fall some drops of the essence 

 of anise on the same mixture placed in the bottom of a glass ; there is now both 

 incandescence and exph)sion. 



To manifest to my auditors the connection which exists between the heat cre- 

 ated by impact and that created by chemical action, I take an exami)le, well 

 known, but on account of its simplicity, serving better than the preceding for the 

 purpose of explanation. The powdered iron, suitably prepared, takes fire when 

 exposed to the air. What is it that occurs in this phenomenon f One of the 

 elements of the air, oxygen, combines with the iron and forms a brown powder, 

 which is called oxide of iron. If the iron be weighed before and after the com- 

 bination, it will be found to have increased in weight ; this proves the fixation 

 of the oxygen in the iron. Now, we shall very well represent to ourselves tlie 

 mechanism of the combination, ])y imagining that the particles of oxygen have 

 been precipitated on the iron and become fixed, just as the stone which falls on 

 the earth remains fixed to the soil. Heat, then, has been created by the impact, 

 and the connection we sought is established. 



The chemical sources of heat are so important in the arts, that I shall more 

 particularly dwell upon them, with a view to point out the recent improvements 

 of which they have been the object. It was only the combustion of charcoal, 

 accelerated by the insufflation of a considerable quantity of air, which for a long 

 time was made use of in industry ; such is the fire of the smelting furnace, which 

 can melt iron, but is incapalde of melting platina. This metal, as precious as 

 gold, could be melted by no known chemical process until quite recently, when 

 the means were devised by M. II. Hainte-Claire Deville. At present we melt It 

 very easily by the combustion of illuminating gas with pure oxygen. In this pro- 

 cess the oxygen contained in a gasometer issues by a copper pipe terminated by 



