D. CHEMISTRY AND METALLURGY. 215 



this term the action of electricity, is raised. In pursuing an- 

 other line of research, namely, the connection between the 

 molecular construction of vapors and their densities, Profess- 

 or Lockyer states that he has recently attempted to bring 

 the spectroscope to bear upon the question. As an example 

 of the behavior of vapors under different temperatures, the 

 observations of the spectrum of dry hydrogen contained in 

 an iron tube whose ends are closed by a plate of glass may 

 be mentioned. The temperature reached by the furnace may 

 be conveniently divided into five stages: First, when the 

 continuous spectrum of the tube extends to the sodium line 

 D, this line, however, not being visible ; second, when the con- 

 tinuous spectrum extends a little beyond D, this line being 

 visible as a bright line; third, when the spectrum extends 

 into the green, D being very bright ; fourth, when the spec- 

 trum extends beyond the green, and D becomes invisible as 

 a line, and the sides of the furnace are at a red heat ; and, 

 fifth", when the tube has, by a special arrangement of Pro- 

 fessor Roscoe, been heated to a white heat. From the ex- 

 amination of twelve or fourteen different substances, Lockyer 

 shows that if similar spectra be taken as indicating similar 

 molecular conditions, then the vapors, the densities of which 

 have been determined, have not been in the same molecular 

 condition among themselves. 12 A, X., 155. 



ASSAYING WITH THE SPECTROSCOPE. 



Some interesting experiments have recently been made in 

 the Assay Department of the United States Mint at Phila- 

 delphia, by Mr. Alex. E. Outerbridge, to ascertain the practi- 

 cability of assaying metals used in coinage by means of the 

 spectroscope. The earliest experiments in this direction were 

 made by Mr. W. C. Roberts, of the London Mint, in 1872, in 

 connection with Mr. Lockyer; the distinguished spectroscop- 

 ist,but with unsatisfactory results. Mr. Outerbridge's experi- 

 ments, as detailed in a paper read before the Franklin Insti- 

 tute October 21, 1874, seem to establish the apparent paradox 

 that the spectroscopic method is in one respect far too sensi- 

 tive and minute, and, in another respect, far from being mi- 

 nute enough to serve the uses of assay. The problem to be 

 solved is, simply stated, to utilize the spectroscope as a means 

 of quantitative as well as qualitative analysis. The cxperi- 



