276 Hartley — The Action of Heat on the Ahsnyption Spectra and 



At 50'^, the solution is quite opaque. 



The best way to prepare this solution in small quantities is to let the anhy- 

 drous salt slowly deliquesce. Thin wedge, gas-light. 



At 20°, very little light transmitted at X 585. 



At 50°, the solution is quite opaque. 



Dilute cobalt iodide, solution, red. This contains a hydrated compound with 

 a greater number of molecules of water than CoIj-GHjO. Thin v/edge, gas-light. 



At 20° to 40°, rays transmitted from X. 685 to 557. 



At 100°, from X 683 to 560. 



Dilute solution of cobalt iodide in glycerine. 



At 20°, red. Rays transmitted from X 561 to 545. 



At 100°, unchanged. 



Cobalt Iodide, CoIa'OHaO. — Solution in alcohol. Amber brown in colour. 

 Thin wedge, oxygen-gas light. 



At 20°, brown. Rays transmited from X 581 to 536 



At 50°, green rays transmitted from X 627 to 503. 



In order to ascertain whether heating an aqueous solution to 100° would yield 

 tbe same compound in solution as would be produced in the dry state by heating 

 the crystallized salt, 5 c.c. of cobalt iodide solution were evaporated down at 100°, 

 and mixed with absolute alcohol till 5 c.c. in volume. This solution was green, 

 and in the thin wedge, with gas-light, the only measurement made at a temperature 

 of 20° was at X 503. When the cobalt iodide in the original aqueous solution was 

 heated to 100° and examined, the transmitted rays were measured at X 588. Both 

 liquids were green, but there was a tinge of a reddish hue transmitted by the 

 aqueous solution. Allowing for the different action of the two solvents, it is 

 quite evident that the same substance was present, but that dissociation had not 

 been complete in the aqueous solution. 



When 55 c.c. of the solution were rendered anhydrous by drying at 160°, 

 alcohol dissolved it readily with, at first, a splendid blue tint, which afterwards, 

 became somewhat greenisli. The salt crystallized out of this solution as a bluish- 

 green substance. This was apparently a solution of the anhydrous salt, for, on 

 placing it in a desiccator over oil of vitriol, it returned to the anhydrous black 

 compound, C0I2. 



Cobalt Sulphate, C0SO4. — An aqueous solution of a red colour. Thin wedge, 

 oxygen-gas light. 



At 20°, spectrum commences at X 715; all rays more refrangible were not 

 interrupted by an absorption band sufficiently strong to obscure the cross-wires. 



\ 

 At 100° C. . Spectrum begins at . . . . . 715 



Absorption Band, 549 to 473 



Spectrum ends at 413 



