204 Harritny— The Action of Heat on the Absorption Spectra and 
above title, one was a preliminary notice,* the other a detailed account of the 
spectra of a number of metallic salts, together with the conclusions arrived at as 
to their chemical constitution when dissolved in water. 
The bare conclusions were published in the Proceedings as an abstract of the 
Paper.t 
The greater part of the memoir was withheld for a time merely for the 
purpose of reducing arbitrary measurements of the spectra to wave-lengths, and 
of inserting Fraunhofer’s lines in the diagrams. It happened that in consequence 
of an illness, and other circumstances which intervened, the experimental details 
here recorded were put aside and overlooked, but the results obtained twenty- 
four years ago have quite recently been confirmed in several particulars. 
The following passage appears in the original communication and is still of 
some interest :— 
‘‘ When a substance is dissolved in water, it is at present an unsolved problem 
what the exact constitution of the resulting liquid really is. If the salt be 
anhydrous like common salt, if may possibly combine with a portion of the water 
to form a more complex molecule, which in its turn is dissolved, or the whole of 
the water may combine with the salt to form a still more complex liquid mole- 
cule. Inthe case of this latter alternative, such solutions are chemical compounds. 
On the other hand, if the substance is one in which water forms an integral part 
of the molecule of the salt, it may be dissolved without the molecule undergoing 
any chemical change, or the salt may be separated from its water of crystalliza- 
tion, and be dissolved as an anhydrous or partially dehydrated substance.” 
There are many observed phenomena connecting the absorption spectra of 
saline solutions with the molecular constitution of the dissolved salts which have 
not yet been published, and at the present time are perhaps of greater interest 
than at any earlier date. 
Scheenbein,= von Babo, Schiff,§ and others have observed the darkening of 
both solids and solutions by the action of heat.|| Gladstone’s{] experiments show 
rather that haloid salts are not decomposed by solution in water, as was formerly 
supposed, and furthermore that cupric chloride in solution, on addition of further 
quantities of water, forms differently hydrated compounds.** 
In 1857, Dr. Gladstone published his well-known Paper ‘On the use of the 
Prism in Qualitative Analysis.”++ The effect of heat on coloured liquids was also 
* Proc. Roy. Soc., vol. xxii., p. 241. + Proc. Roy. Soc., vol. xxili., p. 372. 
+ Jahresbericht, 1852, p. 8301; 1853, p. 312; 1857, p. 72; 1889, p. 58. 
§ Ann. Ch. Phar., ex., p. 203. 
|| Gmelin’s ‘‘ Handbook of Chemistry,” English edition, vol. 5, p. 337. 
q Jour. Chem. Soc., vol. 7, p. 211. *% See also Jour. Chem. Soc., vol. 18, p. 206, 1875. 
tt Jour. Chem. Soc., vol. x., p. 79; Phil. Mag., vol. xix.; Proc. Roy. Soc., vol. ix., pp. 66-74, 1859 ; 
Jour, Chem, Soce,, vol, x1., pp. 36-40, 1859, 
