Chemistry and Physics. 



157 



foil was used. The electrodes* were Ceylon graphite as in other 

 experiments, the sole impurity in which was a trace of magnesium. 

 The following tabulated statement gives the wave-lengths of 

 the lines, together with a description of the spectra photographed 

 from solutions of different strengths : — 



Strength of Solutions or Degrees of Dilution shown 



by per cent 



of Beryllium. 



Beryllium 



^W 1 Per cent. 



scale). 



0-1 p. c. 



01 p. c. 



A(lA , AAAA1 0-00001 



0001 p c. 0-0001 p. c. , 

 1 per cent. 



000001 

 per cent. 



3322-3 Continu- 



Half of 



Very 



Faint in-; Extinct Extinct 



Extinct 



ous line 



line much 

 weakened 



short fine 



dication 







3130-3 ; 



Continu- 



Half of 



Half of Line 



Half line 



Nearly 





ous line 



line 



line wea-' one-half still 



one-half, 







weakened 



kened shorter i strong 



1 



still 

 strong 



•2649-8 I " 



Half of 



Very 



Very Dot Dot 



Dot 





line weak- 



short line 



short line merely 





. 



ened 





Very Dot, 



Dot, 



2493-6 "' 



u 



u 



« 



faint dot scarcely 

 visible 



scarcely 

 visible 



2478-1 " 



Continu- 



Short line 



Very fine Very Fine 



Fine 





ous line 





short line short line short line 



1 1 



short line 



The actual length of the line 2478-1, as rendered by solutions 

 of 0*00001 per cent and 0-000001 per cent strength, is, in the for- 

 mer, 0*07, and, in the latter, 0*05. of an inch. The normal length 

 of the line at this part of the spectrum is 0*22 of an inch. The 

 quantity of substance yielding this spectrum is equivalent to 

 one-millionth of a milligram of beryllium. As I have pointed out 

 in the case of magnesium,! so also is it with beryllium, that the 

 sensitiveness of the spectrum reaction may be increased ten thou- 

 sand-fold by using a larger coil and more powerful condenser, but 

 leaving the striking distance between the electrodes unaltered. 

 The coefficient of complete extinction was therefore practically 

 not attainable for all the lines, or, in other words, the sensitive- 

 ness of the reaction is almost without limit. 



It will also be seen from my description of the spectra, which 

 have been quite recently re-examined, that the coefficient of 

 extinction of the two lines /C 3130*3 and 2478-1 had not been 

 reached by the dilution specified. 



A number of thin sections of the Dublin granite containing 

 microscopic crystals of hexagonal form were examined some 

 years ago. The crystals were supposed to be apatite, but a very 

 carefully executed analysis disclosed the fact that the proportion 

 of phosphoric acid contained in 20 grams of the rocks was almost 



* Phil. Trans.. 1884, Part I, p. 49. 

 f Phil. Trans.', 1884, Part II, p. 325. 



