1884.] Researches in Spectrum Photography. 



421 



March 13, 1884. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The following Papers were read : — 



I. " Researches in Spectrum Photography in Relation to new 

 Methods of Quantitative Chemical Analysis. Part II."* By 

 W. N. Hartley, F.R.S.E., &c, Professor of Chemistry, 

 Royal College of Science, Dublin. Communicated by Pro- 

 fessor G. G. Stokes, Sec. R.S. Received February 28> 

 1884. 



(Abstract.) 



This paper includes an introduction recording the methods which 

 have been proposed by different authors for the quantitative estima- 

 tion of various metallic elements. An account is then given of the 

 length and strength of metallic lines in solutions of definite strength. 

 Under given conditions each solution emits a characteristic spectrum. 

 In the case of magnesium, a minute description is given of the 

 spectra presented by various solutions containing from 1 per cent, to 

 0' 00000001 per cent, of the metal, but in the case of other elements 

 tabular descriptions of the spectra of solutions containing 1, 0*1, and 

 0"01, in some instances O'OOl, of metal are given together with care- 

 fully drawn maps. The substances thus treated of are magnesium, 

 zinc, cadmium, aluminium, indium, thallium, copper, silver, mercury, 

 tin, lead, tellurium, arsenic, antimony, and bismuth. 



The sensitiveness of the spectrum reaction is practically unlimited 

 when applied to magnesium compounds dissolved in water, since it- 

 was shown that with a given length of spark, y ooooooo °f a milligram 

 could easily be detected ; when, however, the strength of spark was 

 greatly increased, but the striking distance between the electrodes left 

 unaltered, the sensitiveness was increased ten thousand-fold. In point 



* For Part I see " Phil. Trans.," Part I, 1884. 



2 G 2 



