RECENT PROGRESS IN RELATION TO THE THEORY OF HEAT. 2-11 



air is itself drawn in, and penetrates into the blow-pipe, which considerably aug- 

 ments the total quantity of air mingled with the gas. In order to evince this 

 fact of the aspiration of the suiTounding air, Ave kindle the jet and direct it into 

 a small furnace of brick, analogous to the fiu'nace of lime, which has served us 

 for melting platina. The flame issues with resonance by a small aperture, and the 

 walls of the furnace are rapidly raised to a red heat. We now let fall powder 

 w)f iron around the holes of the blow-pipe; this powder becomes heated in the 

 furnace and issues with the flame in brilliant sparks. The necessar}' accessory 

 of the blow-pipe consists in a powerful 1)ellows, which impels the jet of air under 

 a pressure of two atmos})hcrcs. For this purpose a pump compresses the atmos- 

 phere in a reservoir, while a tube of resistant caoutchouc conveys the compressed 

 air from this reservoir into the blow-pipe. 



In this way the inconveniences of the nitrogen contained in the air are lessened. 

 In the blow-pipe of M. Wiesnegg, the air is so intimately mingled with the 

 gas that the inertia of the nitrogen ofiFers the least possible opposition to the 

 rapidity of the chemical combination. Now", it is on this rapidity that depends 

 the temperature of the flame. The more rapid the molecular movements which 

 create heat, the higher the point to which the temperatiu-e is raised ; because the 

 environing bodies have not time within a certain limit to absorb that heat. 



I limit myself to these applications of the chemical som'ces of heat, and pass 

 to a source of quite another kind — to that which lias furnished us the highest 

 known temperatures, and which can reduce to vapor the diamond itself. None 

 of the preceding methods enable us to modify this substance ; it is the n;ost 

 refractory of whicli we have any knowledge. 



Conceive a sheet of zinc and one of copper plunged into sulphuric acid, diluted 

 with water. We know that the zinc combines with the elements of the liquid, 

 producing heat. If we unite the two sheets by a metallic wire, the latter becomes 

 heated, which indicates that it is the seat of a peculiar modification. The cause 

 of this modification we name electricity, and we say that the assemblage formed 

 of the acid, the metals and the wire, is traversed by the electric current. Now, 

 if we measure the heat produced in the acid and in the wire, Ave find it to 

 be, for a certain Aveight of zinc dissolved, the same as if the metal Avere simply 

 dissolved in the acid Avithout the wire, Avhich gives passage to the current. The 

 sole diflcrence Avhich exists betAvecn these two modes of operating consists in 

 the heat being difi'erently distributed ; in the act of the dissolution of the. zinc 

 in the acid Avithout an electric current, the heat is only produced at the place of 

 the chemical action ; Avhen there is a current, this heat is produced simultane- 

 ously in all the parts of the circuit traversed by the current. In order to exhibit 

 the heat disengaged in the electric circuit, a battery has been arranged outside 

 of the apartment occupied bA' my audience ; that battery being an assemblage of 

 sheets of zinc and aciduhiled Avaierin Avhich the chemical combination is eiFected, 

 Avhile the metallic Avire Avhich serves to close the* circuit extends to myself for 

 the peiiormance of the ex])criments. At this moment the Avire is divided, and I 

 hold in my hand its two extremities ; I touch Avith them the two ends of a fine 

 wire of platina, 50 centimetres in IcJigth, so that the circuit is now closed. The 

 cun'ent passes, and we see that the Avire of i)latina is heated to a Avhitc red ; it 

 in fact melts, and no doubt therefore can remain of the disengagement of heat 

 which I announced. The two wires Avith Avhich I touched tlie platina were of 

 Copper, and their diameter Avas about two millimetres; these also Iuia'c become 

 heated, l)ut the elevation of their temperature Avas slight, simply because of their 

 thickness. 



I shall not seek on this occasion to ex])lain how electricity effects the distribu- 

 tion of heat in the circuit of the battery ; 1 propose merely to mention this means 

 of producing heat, the discovery of which avc owe to V«jlta, and which dates l)Ut 

 a half centmy ago. It has been seen that this source of heat is of chemical 

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