3t KNOVv'LEDGE Of the distribution of energy in the visible spectrum of an acetylene flame has become important within the last few years through the use of this flame, in cylindrical form, in investigations of the visibility of radiation. It can be shown by computation that the data on acetylene published by Coblentz form a curve in the visib!e spectrum which will not agree with that of a black body at any temperature to better than 7 or 8 per cent. As this would mean that no color-match could be obtained and as previous experience of the authors had led to the conclusion that the energy curve of acetylene differed in shape from that of a black body only in the extreme red, a short investigation was undertaken to verify this conclusion.
Tungsten lamps whose current color-temperature relation was carefully determined in this laboratory were sent to the Eastman Kodak Company and to the Bureau of Standards with the request that they be compared with the acetylene flame and the current for color match be found. The results gave an average value of 236o: K. ยฑ IO ยฐ K., and neither laboratory reported any difficulty in obtaining a match in color. However, the Bureau of Standards reported a difference amounting to about 75ยฐ K. between the flame as given by the Eastman standard burner and that given by the " Crescent Aero " burner, the latter being higher.
The spectral distribution of the flame was measured by means of a speetrophotometer and a spectral-pyrometer and the results gave a curve agreeing within the limits of error with that of a black body at 236o ยฐ K. In the extreme red, beyond o.7o/, there was indication of a higher emissivity for the acetylene. A photographic method gave results corroborating those just mentioned.
A test of the sensibility of the color match method to show differences in the spectral energy curve, showed that if two spectral curves matched at o.5/. and o.7/. and differed by as little as * Communicated by the Director.