March 15, 1888] 



NATURE 



471 



The apparatus which I constructed several years ago 

 makes it possible to bring bodies to a temperature 

 approaching that of the fusion of platinum, whilst main- 



taining them in a gaseous atmosphere, of which the 

 nature and pressure may be varied at will. 



This apparatus (Fig. 2) is composed of a mass of steel 



Fig. 



-Apparatus of M. Cailletet. a, mass of steel wuh cylindrical bore, with its stopcock b (see the details in Fig. 2) ; G, mirror permitting the reaction 



to be seen ; M, manometer ; l, amperemeter. 



A, in which there has been hollowed out a cylindrical 

 space of about a quarter of a litre capacity. This species 

 of test-tube may be closed by means of a metallic stop- 



FiG. 2. — Explanatory figure :— (1) Arrangement for obtaining the electrical 

 arc. The insulated charcoal is shaped in the form of a crucible, (z) 

 Arrangement with v^fire of platinum rolled spirally. 



cock, B, furnished with screw. Two copper wires are 

 fixed to this movable portion ; the one, c, is insulated, 

 whilst the other, D, is in contact with the metal. At the 



ends of these two wires there is fixed, according to the 

 requirements of the experiment, either a sheet of platinum 

 moulded into the form of a crucible, or a wire of platinum 

 rolled spirally, a kind of receptacle for the body experi- 

 mented on, and which is brought to the desired tempera- 

 ture by the passage of an electric current. Two or three 

 accumulators are sufficient for these experiments. A 

 fragment of gold, placed in the spiral, melts in a few- 

 seconds. When it is desired to maintain the temperature 

 long, the exhausted accumulators are replaced by others 

 in readiness, simply by use of a commutator. The high 

 temperature developed by the electric arc may also be- 

 turned to account ; in that case two charcoal rods are 

 arranged, of which one, movable, is fixed to the extremity 

 of a screw, D, capable of being adjusted from the outside 

 in order to place it in communication with the other 

 charcoal rod, E, insulated and shaped in the form of a 

 crucible. 



The block of steel is pierced by an orifice, F, connected 

 by a metallic capillary tube with the reservoir which con- 

 tains the compressed gas. A window furnished with a 

 thick glass, G, allows the phases of the experiment to be 

 followed by looking in an inclined mirror, so as to be 

 secure from all danger in case of the glass breaking. 

 Lastly, the gases contained in the apparatus may be col- 

 lected, by means of a stopcock at the screw H, in cases 

 where it is desirable to analyze them. 



The gas used for the experiments is compressed 

 previously in a holder by means of the mercurial pump, a 

 description of which I have already published ; it is also 

 easy to employ the carbonic and sulphuric acid furnished 

 by commerce. 



A metallic manometer fixed to the apparatus renders \t 

 possible to ascertain that the pressure of the gases exer- 

 cises an energetic cooling influence upon the bodies which 

 are heated by the electric current. 



Thus, the current which causes the fusion of the wire 

 or sheet of platinum produces only a sombre red temper- 

 ature when the pressure is sufficiently great. I have beea 

 able to lessen this cause of cooling, by placing the body 

 on which I was experimenting in a small test-tube, whiel* 

 resists the motion of the gases, and which is not repre- 



