Specific Refraction and Dispersion of Light by the Alums. 163 



Alum. 



Specific 

 gravity. 



^A' 



"G- 



d 



HG — pk 



d 



pfiA-1 



d 



Ammonium Aluminium.. 



1631 



1-4542 



1-4692 



•2784 



•0093 



252-23 



Sodium „ 



1-667 



1-4342 



1-4480 



•2604 



•0083 



238-52 



Methylamine „ 



1-568 



1.4496 



1-4636 



•2867 



•0090 



267-68 



Potassium ,, 



1-735 



1-4516 



1-4661 



•2603 



•0083 



246-81 



Eubidium „ 



1-852 



1-4513 



1-4662 



♦2437 



•0080 



253-69 



Caesium ,, 



1-961 



1-4536 



1-4682 



•2313 



•0074 



262-31 [ 



Thallium „ 



2-257 



1-4914 



1-5108 



•2177 



•0086 



278-34 



Ammonium Chromium . . . 



1-719 



1-4781 



1-4959 



•2781 



•0104 



26594 



Potassium „ 



1-817 



1-4754 



1-4931 



•2616 



•0098 



261-22 



Eubidium „ 



1-946 



1-4756 



1-4932 



•2444 



•0090 



266-69 



Caesium ,, 



2043 



1-4753 



1-4928 



•2326 



•0086 



275-50 



Thallium 



2-386 



1-5158 



1-5381 



•2161 



•0092 



286-90 



Ammonium Iron 



1-713 



1-4783 



1-4998 



•2792 



•0126 



26915 



Potassium ,, 



1-806 

 1-916 

 2-061 



1-4757 

 1-4763 

 1-4772 



1-4960 

 1-4970 

 1-4984 



•2631 



•2486 

 •2315 



•0112 

 •0108 

 •0103 



26503 

 273-21 

 275-95 



Rubidium ,, 



Caesium ,, 



Thallium ,, 



2-385 

 2-065 

 1-962 



1-5155 



1-4586 

 1-4606 



1-5411 

 1-4740 

 1-4758 



•2161 

 •2221 

 •2348 



•0108 

 •0074 



•0077 



288-85 

 269-63 

 264-43 



Rubidium Indium 



Rubidium Grallium 



Messrs. Topsoe and Christiansen* have also published the 

 refractive indices of three alums for the lines C, D, and F ; 

 and as they have given the specific gravity, their observations 

 are available for the same purpose. The index for A has been 

 calculated from these data. 



Alum. 



Ma- 



/*c- 



/iA — 1 



d ' 



pf*A-l 



d 



Potassium Iron Sulphate 



Ammonium Iron Sulphate 



Potassium Aluminium Seleniate 



1-4751 

 1-4789 

 1-4748 



1-4783 

 1-4821 

 1-4773 



•2597 



•2786 

 •2409 



261-37 

 268-56 



272-98 



How far do these figures support the former conclusion, 

 that a salt has the same specific refraction whether in a solid 

 form or in solution ? 



For this purpose determinations were made of the refraction 

 for A in aqueous solutions of the first two alums in M. Soret's 

 list. Deducting the amount due to the solvent, the following- 

 values were arrived at : — 



Dissolved. Crystallized. 



Ammonium Aluminium alum . . '2780 '2478 



Sodium Aluminium alum . . . -2(513 *2604 



* " Krystallografisk-optisk Undersoegelser," Dot K. Danske Viden- 

 skabernes Sehkabs Skrifter, 1873, p. 622. 



M2 



