SOLUTIONS. 



103 



The reflection band of the solid crystal does not agree with the one 

 found by Pfund at 9.05 /*, which is the mean value of the present curve. 

 In the present curve the maximum is evidently complex. Neither does 

 the maximum of the solid and that of the solution agree, which is prob- 

 ably to be expected. In fact, the study of solutions was undertaken to 

 test this very point. 



COPPER SULPHATE (CuSO4+sH*O). 



In fig. 87, curve a is for a saturated solution of copper sulphate in 

 which the maximum of reflection is very sharp at 9.15 p. For a solid 

 crystal of this material the maximum (curve c) coincides with that of the 

 solution. The reflection band found 

 by Porter at 2.3 /* really occurs at 3.3 /*. 

 The former value is due to an error in 

 computation. 



ZINC SULPHATE (ZnSO*+7H 2 O). 



The reflecting power is somewhat 

 higher than in the preceding com- 

 pound. The maximum (curve b, fig. 

 87) occurs at 9.2 /* for a saturated 

 solution of this compound. 



SODIUM SULPHATE (NaSCX+ioHiO). 



The selective reflection of a satu- 

 rated solution of this compound is 

 shown in curve a, fig. 88. The maxi- 

 mum occurs at 9.2 p, while Pfund 

 found it at 9.02 /*, using the surface of PJG 

 a mass of crystals. 



MERCURY (Hg). 



to 



HjU 



-Sodium sulphate (a) ; Potassium 

 sulphate. 



Several observations were made on the reflecting power of mercury, 

 but the present arrangement was not well adapted to determine the 

 absolute reflecting power, and no thorough examination was made. 

 The chief difficulty is in having the two surfaces at the same level. 

 Values of reflecting power as high as 85 per cent (purity not known) 

 were observed, while the computed value is 90 per cent at 12 p. 



Earth tremors had but little effect on the surface ; while, if pure dust- 

 free mercury be used, this is the best substance available to compare the 

 effect of the polish upon the reflecting power in the region of short 

 wave-lengths. In fact, the determination of the absolute reflecting 

 power throughout the spectrum would be an interesting study by itself. 



