Chemical Compounds. 



15 



14 



13 



12 



11 



10 



9 



8 



■ 7 



6 



5 



• 4 



3 



625-6 

 624-2 

 617-8 

 616-3 

 611-7 

 610-0 

 606-8 

 605-1 

 602-6 

 600-2 

 598-8 

 595-4 

 594-1 



Differ- 

 ence. 



1-4 

 6-4 

 1-5 

 4-6 

 1-7 

 3-2 

 1-7 

 2-5 

 2-4 

 1-4 

 3-4 

 1-3 



-3 



-2 



-1 



+ 1 



+ 2 



3 



4 



5 



6 



7 



8 



9 



10 



594-1 

 591-4 

 590-8 

 587-5 

 583-5 

 580-1 

 576-5 

 573-0 

 569-1 

 565-8 

 562-2 

 558-8 

 555-5 



Differ- 

 ence. 



2-7 

 0-6 

 3-3 

 4-0 

 3-4 

 3-7 

 3-5 

 3-9 

 3-3 

 3-6 

 3-4 

 3-3 



447 



Differ- 

 ence. 



+ 10 555- 



11 552- 



12 550- 



13 547- 



14 545- 



15 543- 



16 541- 



17 539- 



18 535- 



19 533- 



20 532- 



21 529- 



22 527" 



2-7 

 2-4 

 2-8 

 2-4 

 2-2 

 2-0 

 1-6 

 3-6 

 2-0 

 4-6 

 3-0 

 1-4 



In order that the whole of these lines should be observed, it 

 was necessary to vary the thickness of the absorbing layer. 

 For this purpose the bromine vapour was contained in a 

 wedge-shaped glass vessel ; the light was allowed to pass 

 through the thicker part when observations were made in the 

 red, and through the thinner part when observations were 

 made in the blue. 



At a temperature of about 20°, the lines from — 1 near D 

 to +22 in the blue were recognizable with a bromine layer 

 10 millims. in thickness. By increasing the thickness of the 

 layer the whole of the lines became more intense, and the lines 

 — 2, —3, to —14 in the red gradually appeared. The fine 

 lines appearing as shading in the blue gradually became more 

 apparent, extending towards the red until the space between 

 any two lines became equally dark; continuous absorption 

 thus spread slowly towards the red. 



With a layer 10 millims. in thickness the spectrum between 

 the lines — 1 and + 22 was observed. 



With a layer 6 millims. in thickness the spectrum between 

 the lines — 6 and +12 was observed. 



With a layer 8 millims. in thickness the spectrum between 

 the lines —11 and +8 was observed. 



Increasing the thickness of the layer thus produced an equal 

 (intensifying) effect upon all portions of the spectrum, but did 

 not cause changes in special parts of the spectrum. Increasing 

 the thickness of the absorbing layer, then, only caused the 

 spectrum to become more marked in its character. 



Observations on the absorption-spectra of iodine and of ni- 

 trogen tetroxide confirmed those made with bromine. 



Alteration of temperature produces different effects upon 

 different parts of the spectrum. 



