NICHOLS. — THE VISIBLE RADIATION FROM CARBON. 89 



of this gas, according to Le Chatelier,* would be, when burned in air, 

 2100° to 2420°. Measurements with Le Chatelier's pyrometer, on the 

 other hand, made by V. B. Lewes,! g^ive temperatures lower than those 

 of ordinary gas flames. Lewes found for the obscure zone 459,° for the 

 edge of the luminous zone 1411,° and for the region near the summit of 

 the luminous zone 1517°. Sraithells, | upon the appearance of the data 

 given by Lewes, described a series of experiments for the purpose of 

 showing that the temperature of the flame reaches, in point of fact, very 

 much higher values than those given by that author, and that in many 

 portions it is higher than the melting point of platinum. 



It can be easily shown by inserting wires of platinum into the flat 

 acetylene flame obtained from any one of the forms of burner usually 

 employed, that while the thicker wires remain unmelted, those of very 

 small diameter are readily fused. I found, for example, that a wire 

 havine a diameter of 0.0<»82 cm. became fused at the end with the for- 

 mation of a distinct globule, before the metal had penetrated the outer 

 luminous layer of the flame, whereas wires of 0.01 cm. or of larger 

 diameter remained unmelted. The experiments of Waggener § show 

 that there are portions of the flame of the Bunsen burner in which it is 

 possible to melt platinum, while MacCrae, 1| working with a platinum- 

 rhodium element, found for the hottest region in the Bunsen flame 1725°. 

 It will be seen from the experiments to be described in this paper, that 

 MacCrae's determination, which was made with wires having a diameter 

 of 0.02 cm., is not incompatible with the observations of Waggener and 

 others. Smithells, in the paper just cited, describes the melting of 

 platinum wires having a diameter of 0.01 cm., in various parts of the 

 outer sheath of a flat flame of illuminating gas. Pellissier, 1[ in com- 

 menting upon Lewes's measurements, refers to experiments in which 

 minute wires of platinum, made by Wollaston's method of silver 

 plating, drawing, and subsequent dissolving of the silver coating, when 

 thrust into the flame of a candle, melted instantly. I have not been able 

 to find other printed reference to these observations and do not know 

 with whom they originated. An attempt to repeat the experiment with 

 a Wollaston wire having a diameter of 0.0011 cm. resulted in the ready 



* Le Chatelier, Comptes Rendus CXXL 1144 (1S95). 



t Lewes, Chem. News, LXXI. 181 (1805). 



J Smithells, Journal of the Chemical Society, LXIX. 1050 (1895). 



§ Waggener, 1. c. 



II MacCrae, Wiedemann's Annalen, LV. 97. 



t Pellissier, L':fcclairage a I'ace'tylene (Paris, 1897), p. 186. 



