1876.] 



Absolution- Spectra of Iodine, 



49 



without causing it either to be dissipated in vapour or to run together. 

 The liquid iodine appears to be more transparent than the solid ; 

 for a layer which appears a deep red colour by transmitted light when 

 hot, sometimes becomes perfectly opaque on cooling. "WTien hot it 

 is also of a deeper red than when cold ; and the spectroscope shows that 

 while the less-refrangible rays of the spectrum are freely transmitted, 

 there is more absorption of those of mean refrangibility than is the case 

 with solid iodine. 



rig. 3 shows the absorption-spectrum as deduced from five observations. 

 Just as is the case with solid iodine, light of a wave-length of about 650 

 suffers the least amount of absorption during its passage through a layer 

 of iodine. 





1 1 • 





1 





r t 1- I — 1 — I T , — 1 — I — 1 



Iodine in Solution. 

 As I have before mentioned, the liquids in which iodine is soluble may 

 be divided into two classes : first, those with which it forms brownish-red 

 solutions, as alcohol, ether, ethyl bromide, Dutch liquid, benzole, glycerine, 

 potassium iodide in an aqueous solution, hydrogen chloride, &c. ; second, 

 those with which it forms violet solutions : this latter class is less nume- 

 rous, and as far as I have hitherto been able to ascertain by actual experi- 

 ment, only consists of the following substances — the bisulphide, tetra- 

 chloride, and monochloride of carbon, chloroform, phosphorous terchloride, 

 tin tetrachloride, and under certain circumstances, as will be hereafter 

 mentioned, hydrogen sulphate. In "Watts's ' Dictionary of Chemistry,' 

 vol. i. p. 881, it is stated that the solution of iodine in chloral has a purple 

 colour. 



In order to obtain solutions of iodine of a known strength, some of 

 the liquids in which it is soluble being very volatile, a small ghass weigh- 

 ing-tube closed mth a cork was nearly filled with iodine which had been 

 crushed small with the edge of a platinum spatula. A stoppered flask 

 holding 2o c. c. was filled with the liquid in which the iodine was 

 to be dissolved ; and the tube having been weighed, a small quantitv of 

 iodine was shaken out of it, and the tube again weighed, and so on, 

 till the desired amount had been added to the liquid. 



In this way solutions of iodine in bisulphide and tetrachloride of carbon, 

 VOL. XXV. E 



