PETROLOGICAL ABSTRACTS AND REVIEWS 531 



origin, but thinks until they have been seen to fall, that their source is 

 to be found only in the conditions under which they occur. 



A. J. 



Merwin, H. E. "A Method of Determining the Density of 

 Minerals by Means of Rohrbach's Solution Having a Standard 

 Refractive Index," Amer. Jour. Sci., XXXII (191 1), 425-28. 

 After making specific-gravity determinations by means of Rohr- 

 bach's heavy solution, the writer determines the density of the latter by 

 means of its refractive index. A comparative table of values of density 

 at 20° C. and corresponding refractive indices is given. 



A.J. 



Merwin, H. E. "Quartz and Fluorite as Standards of Density and 

 Refractive Index," Amer. Jour. Sci., XXXII (191 1), 429-32. 

 Quartz and fluorite from different parts of the world were compared 

 and it was found that at ordinary room temperature the density of pure 

 quartz is 2 . 6495=*= . 0010 and of pure fluorite 3 . i8o=t= . 001. By sodium 

 light the refractive index (e) of quartz was found to be i . 5443 — i . 5442, 

 and of fluorite, 1.4338+ and 1.4338 — . 



A. J. 



Merwin, H. E. "Media of High Refraction for Refractive Index 



Determinations with the Microscope; Also a Set of Permanent 



Standard Media of Lower Refraction," Jour. Wash. Acad. Sci., 



Ill (1913), 35-40. 



To fill the gap between fluids having refractive indices from 1.33 to 



1 . 80 and from 2.1 to 2.4, Merwin proposes solutions of iodoform, tri- 



iodide of arsenic, tri-iodide of antimony, tetra-iodide of tin, and sulphur 



in methylene iodide. With various proportions dissolved in 100 parts 



of methylene iodide, fluids of refractive indices between i . 764 and i . 868 



are obtained. Fluids from i . 74 to 2.28 were obtained by dissolving 



arsenic trisulphide in methylene iodide near its boiling-point. Merwin 



also prepared resin-like substances with indices between i . 68 and 2.10 



by dissolving tri-iodides of arsenic and antimony in piperine. For media 



between 2 . i and 2 . 6, he used mixtures of amorphous sulphur and arsenic 



trisulphide. Other media were mixtures of piperine and rosin for 



indices between 1.546 and 1.682, and mixtures of rosin and camphor 



for 1. 5 10 to 1.546. 



A. J. 



