[ 253 ] 



VIII. 



THE ACTION OF HEAT ON THE ABSORPTION SPECTRA AND CHEMICAL 

 CONSTITUTION OF SALINE SOLUTIONS. By W. N. HARTLEY, F. R.S., 

 Royal College of Science, Dublin. (Plates XVII. to XXII.) 



[Eeacl Febeuaet 21, 1900.] 



CONTENTS. 



PAGH 



Introduction, 253 



Early experiments of Schoenbein, von Babo, and SchifF, 



on the constitution of Saline Solutions, . . . 254 



Researches of Gladstone, Bunsen, Melde, Burger, H. W. 

 Vogel, Landauer, Morton and Bolton, and Russell, 

 on the Absorption Spectra of Solutions, . . 254 



Method of Experimenting, ...... 256 



Part I. 



The Absorption Spectra of Nickel and Copper Salts 

 described and measured, ..... 258 



Spectra of Anhydrous Substances and Salts not 

 dehydrated at 100° C 259 



The molecular weight of Anhydrous Haloid Salts 

 determined by Beckmann's method, . . . 261 



The Composition of the Hydrates of Nickel Bro- 

 mide and Iodide determined 262 



Part II. 



Spectra of Cobalt Salts described, . . .267 



Method of photographing the Absorption Spectra in 



the region of Coloured Rays, .... 268 

 Varying limits of accuracy in the measurements of 



Absorption Spectra, 269 



Cobalt Salts form Oiychlorides, Oxybromides, and 



Oxyiodides, ....... 278 



Evidence that the Haloid Salts are not Hydrolysed, 278 



Part III. 



The action of heat on the Absorption Spectra of 

 Chromium Salts. Measurements of Spectra, . 279 



Change in the Chemical Constitution of Chromium 

 Salts when their solutions are heated, . .281 



The experiments of Schrotter, Kruger, and Loewel 

 discussed, 283 



Thermo-chemical researches of Recoura on the 

 Constitution of Chi-omium Salts, . . . 286 



Chromoxalates and Chromo-sulphates, their con- 

 stitution, 287 



Lapraik's investigation of the Spectra of Chromium 

 Salts, anil evidence of the existence of two 

 Chromoxalio Acids, ..... 287 



Pabt IV. 



Spectra of Salts of Uranium, Didymiiun, and Per- 

 manganates described, ..... 287 



Measurements of Spectra of various Didymium 

 Salts, . ._ ._ 288 



Reference to the investigation of Bunsen and of 

 H. Becquerel 289 



FA6E 



Photographed Spectra of Didymium Sulphate, 

 Praseodym Ammonium Nitrate, and Neodym- 

 ammonium Nitrate, ...... 290 



Recent experiments of Muthmann and Stiitzel on 

 Neodym and Praseodym Salts, and of Ostwald 

 on Permanganates discussed, .... 292 



Deductions and Conclusions, .... 293 



The Spectrum of Potassium Permanganate de- 

 scribed and measured, 294 



Part V. 



The Molecular Constitution nnd Dissociation Fheno- 

 mena of Saline Solutions. 



The action of different Solvents, . . . .296 



The effect of heat on the Absorption Spectra. 



Conclusion I., 297 



Reactions of Salts in solution at different tempera- 

 tures, 298 



Conclusion II., 298 



Crystallized Hydrates generally dissolve in cnld 

 water without dissociation of the Molecule. 

 Conclusion III., . . . . . .298 



Dehydration of a Crystalline Hydrate in an Aqueous 

 Solution by Alcohol and the recrystallization of 

 the original Salt on Evaporation, . . . 300 



No evidence of Alcoholatcs being formed. Experi- 

 ments of Potilitzin on Cobalt Chloride, . . 301 



Tabulated statements of the changes in colour of 

 Aqueous Solutions of Salts, &c., . . . 302 



Evidence of several Hydrates of the one Salt 

 being simultaneously present in the same Solu- 

 tion, 303 



Remarkable behaviour of Cupric Bromide, . . 303 



Conclusions IV. and V., ..... 304 



The colour relations of" Solid Salts to those of the 

 same substances in Solution, .... 304 



The most stable Hydrates in concentrated Solutions 

 ol^ Cupric Chloride and Bromide, and Nickel 

 Bromide and Iodide, ..... 306 



Evidence of the Compounds formed in some 

 Aqueous Solutions, ..... 306 



Reference to Riidorflf's, De Coppet's, and Thomsen's 

 experiments on the formation of Liquid Hy- 

 drated Salts, 307 



Conclusion VI 307 



Conclusion VII., and references to Ostwald's and 

 Ewan's Observations on the Absorption Spectra 

 of very Dilute Solutions, ..... 307 



Summary and General Conclusions, . . 308 to 312 



Introduction. 



In the years 1874-75 the Secretary of the Royal Society (now Sir George Gabriel 

 Stokes) did me the honour of presenting for publication two papers with the 



TEANS. KOr. PtJB. SOC., N.8. VOL. VII., PAET VIII. 



2N 



