APPENDIX V. 131 



reflection (equivalent to metallic absorption) at 8.69 /x, curve d, is due 

 to Aschkinass.^ 



The method of selective reflection seems better for studying minerals 

 far in the infra-red. In fact it seems the proper method for making 

 an extensive study of minerals containing water of crystallization, since, 

 with few exceptions, they can not be obtained in thin films, especially 

 for minerals containing several molecules of water of crystallization. 



As already indicated, the unusual similarity of the curve of selenite 

 and the great dissimilarity of the barite and the mica curves to that of 

 water indicate that water of crystallization is not different from ordi- 

 nary water, as mentioned by Konigsberger. The present investigation 

 at 3.0 to 6 /A is additional evidence to this effect. 



The observations are of considerable significance, for,^ "in the pres- 

 ent state of our knov/ledge it is impossible to say that there is an abso- 

 lute difference between the so-called water of constitution and water of 

 crystallization, and not merely one of degree," although there is some 

 evidence that there is a difference. The above curves are so marked 

 that it is difficult to conceive how they can be one and the same thing. 



I am indebted to Prof. A. C. Gill, of the department of mineralogy, 

 for these two minerals. 



'Aschkinass: Ann. der Physik, (4), i, p. 42, 1900. 



^Encyc. Brit., 5, p. 505. See also Role of Water of Crystallization in Salts of 

 Organic Acids, by T. Salzer, Zeit. f. Phys. Chera., 19, p. 441, 1896. 



