240 KECENT PEOGEESS IN EELATION TO THE THEOEY OF HEAT. 



a tip of platina. This pipe is in tlie axis of a second and larger pipe of cop- 

 per, wliose extremity is also of platina. The illuminating gas issues forth, fill- 

 ing the interval comprised between the two pipes. We have thus a jet formed 

 by a mixture. We kindle this jet and introduce it into a furnace composed of lime ; 

 the flame whirls with resonance in the midst of the furnace, heats it intensely, and 

 issues by a lateral opening. It is by this opening that we introduce the platina 

 under the form of tliin lamina?. Each lamina disappears as if swallowed up, 

 and a s])arkling liquid trickles to the bottom of the furnace. 



We stop the jet of flame and uncover the furnace; the liquid platina is so 

 dazzling that we may extinguish the gas burners in the hall, and we are iUu- 

 minate<l as b}'^ the electric light. We pour the liquid in a vase of limestone, 

 and can see its perfect fluidity. By degrees it grows cool in the air, and finally 

 becomes a solid ; but it is so heated that it will remain a long time luminous. 

 When there is need -but of a moderate heat, the combustion of illuminating 

 gas by the ordinary air is often preferalde to that of coal, and the construction 

 of apparatus for wanning by gas is at present carried to great perfection. The 

 principal improvement is due to the distinguished German chemist Bunsen, who 

 has devised an excellent arrangement for completel}'' burning the gas. 



The Bunsen burner is essentially formed of two concentric pipes ; the gas 

 is conducted into the inner one ; the external pipe being open at the two extrem- 

 ities, the atmospheric air naturally enters, mingles with the gas, and it is this 

 mixture which is kindled. The flame is but slightly luminous, but very hot; if 

 we prevent the access of air, the flame becomes brilliant, because the carbon of 

 the gas is not immediately burned by the oxygen of the air, and it remains for 

 some time as a solid dust raised to a very high temperature. It is the presence 

 of the free carbon which enables the flame to be illuminative ; the form of the 

 burner for giving light is such that the carbon is not burned so soon as the hydro- 

 gen of the gas, while in the bunier of Bunsen it is burned at the same time. A 

 single one of these burners, of a suitable size, is sufficient to melt silver. 



At present the Buneen burners are of the greatest service in our laborato- 

 ries; they are employed for heating the tubes for chemical analj'sis, and quite 

 recently an arrangement has been contrived which secures for this mode of heat- 

 ing the greatest regularity. The mixture of air and gas issues by some sixty 

 small holes pierced in a cylinder of fire-proof earth, and all these small flames 

 raise the cylinder to a red heat, in such sort that the caloric is uniformly difluscd 

 in all directions. Some hundred jets of this sort, suitably disposed around a 

 glass tube, raise all its points to the same temperature without risk of fracture 

 or distortion of the tube. Is it possible to attain a temperature sufficient for the 

 fusion of platina by burning simply a mixture of air and coal-gas ? It is the 

 presence of nitrogen, an element of' tlie air altogether inert, Avhich hinders the 

 temperature of combustion of such a mixture from being as high as that of the 

 mixture of gas and i)ure oxygen. The nitrogen appropriates a part of the heat 

 created by the chemical combination, and moreover it embarrasses the contact of 

 the oxygen and the combustible. The employment of air Avould nevertheless 

 be much preferable to that of pure oxygen, wdien an industrial interest is in ques- 

 tion, on account of the dearncss of tlie latter and the difficulty of its prepara- 

 ration. Hence it has been sought to solve this problem ; and, by applying to 

 the blow-pipe of j\I. Schlpesing the principle of the ventilator of M. Demontdesir, 

 M. Wiesnegg has succeeded in melting platina by means of a mixture of air 

 and coal gas. 



In the blow-pipe of M. Wiesnegg, as in that of M. Schlsesing, compressed air 

 arrives by a small orifice at the bottom of a tube, and the gas penetrates into 

 this tube by a lateral tubulure in advance of the jet of air. The mixture is 

 kindled at the outlet from the tube. But in the blow-pipe of M. Wiesnegg, the 

 air being very strongly compressed, issues w'ith great velocity ; it briskly draws 

 in the gas, and holes being })ierced around the orifice of efflux, the atmospheric 



