i8 



INFRA-RED TRANSMISSION SPECTRA. 



All have found water extremely opaque to infra-red radiation, so that 

 the film had to be reduced to a few thousandths of a millimeter in order 

 to be able to study it at all. In fig. i are given the absorption curves 

 of water is found by Aschkinass. His values of the maxima are slightly 

 greater than those found by others, but this is simply due to a fault in 

 his calibration. The curves for the different thicknesses (0 = 0.05; 



90 % 



O I 2 3 4 5 6 



FIG. 2. Selenite (a and c) ; Anhydrite (b). 



b = o.oi mm.) illustrate very well what we are to expect in the case of 

 minerals containing several molecules of crystal water. For a very 

 much thinner film (curve c = 0.001 mm.) by the writer 1 the absorption 

 band at 4.75 //, has entirely disappeared. 



SELENITE (CaSO4+2H 2 O) ; ANHYDRITE (CaSO). 



(Figs. 2, 3, and 4. Selenite: Monoclinic, cleavage parallel to b; t = 0.648 mm. 

 Anhydrite: Orthorhombic, cleavage piece parallel to c; t 0.656 mm. From 

 Stassfurt, Germany.) 



Of all the minerals studied containing water of crystallization these 

 two are the most conspicuous for demonstrating the effect of the presence 



1 Phys. Rev., 20, p. 257, 1905. 



