Chemical Constitution of Saline Solutions. 265 



Composition and Formula. 



Calculated for Found. Erdmann's 



Nil2-7H«0. Per cent. Analysis.* 



Ni, . . . 13-38 13-29 (mean) 



Nil, 72-82 



I, . : . 57-86 58-02 ■' 



HoO, . . . 28-75 28-80 (meau) BH^O, . . 27-18 



99-99 100-11 10000 



These numbers agree so very closely with the composition of a salt of the 

 formula NiL'THoO that I have no hesitation in assigning it that formula, though it 

 is usually stated to be a hexahydrate. 



It is completely dehydrated by standing over sulphuric acid and by heating to 

 100° C. When dried without the action of heat, it is a black amorphous powder. 



These salts were prepared in my laboratory, and analysed by Mr. J. A. 

 Cunningham, B.A., A.R.C.Sc.I. 



PART II. 

 Spectra of the Second Kind. 



The salts of cobalt for the most part present spectra characterised by broad 

 absorption bands. The bands are readily weakened in intensity by diluting 

 saturated solutions. In this respect the spectra differ widely from those of uranium 

 salts, salts of (didymium) praseo- and neo-dymium, all of which exhibit absorption 

 bands of the third kind and have been closely studied. 



The differences arise from differences in the constitution of the spectra, and 

 may best be exemplified by stating that not only are they greatly modified by 

 dilution, but very slight differences in the thickness of the layer of liquid present 

 very different spectra. While in the case of uranium compounds and didymium 

 salts, a small difference in thickness of liquid or even great dilution does not alter 

 the intensity or the width of the absorption bands in a proportionate degree. 

 This is best shown by integrating the spectra, taking for ordinates the proportional 

 thickness of liquid, and for the abscissae the wave-lengths or oscillation-frequencies 

 of the rays absorbed. The curves so obtained differ so very widely in the two or 

 three classes of salts that they cannot be reproduced as suitable illustrations. 

 There can be no doubt, when all the chemical evidence available is taken into 

 consideration, that the spectra belong to substances quite differently constituted. 

 H. W. Vogel| examined a number of inorganic coloured substances, such as 



* Jour, fiir priikt. Chem., vol. 7, p. 254. 



f Ueber die Versohieclenlieit der Absorptionspectra eines und desselbeu StofPs. Ber., vol. xi., p. 913, 

 1878. 



