278 The American Naturalist. [March, 
wies” as microscopic crystals, A mixture of 65 parts SiO, + 3Aq, 
44 parts Al,O, + 3Aq, and 33 parts gypsum, heated in a platinum 
crucible with an excess of Glauber’s salt, yielded tiny cubes and dode- 
cahedra of hauyne or sodalite. When heated with an excess of Na, 
SO, + Na Cl a substance was obtained that is supposed to be an iso- 
morphous mixture of the two minerals above mentioned, and in addi- 
tion some sodalite crystals were produced. When heated with Na Cl 
alone sodalite only resulted. 
Methods and Instruments.—A simple method for determining 
the value of the optical angle in thin sections of minerals is described 
by Lane.” It consists essentially of the measurement of the angular 
distance between the hyperbolas of the biaxial interference figure by 
means of the sub-staye mirror. 
A cheap form of crystal refractometer constructed on the same prin- 
ciples as the larger Zeiss instrument has been made by Czapske.” The 
height of the complete instrument is only 25 cm. It is suitable for 
all ordinary refraction work. 
` An Appendix to the ‘‘Gems of North America.’’—Mr. 
Kunz has issued an appendix to his valuable ‘Gems and Precious 
Stones of North America’™ that brings the volume up to date. Most 
of the material in the appended chapter has appeared in the journals, 
but some of the information it contains is new. The author states that 
the sapphire gravels of Ruby Bar, Montana, and the turquoise mines 
of New Mexico are now being worked by companies that expect their 
outlay of capital justified by a goodly yield of gem material. The 
turquoise company has already taken from their diggings about a 
hundred thousand dollars worth of gems. 
Neues. Jahrb. f. Min., etc., 1892, II, p. 139. 
6Science, Dec. 23, 1892, p. 354. 
2™Neues. Jahrb, f. Min., etc., 1892, I, p. 209. 
**Cf., AMER. NATURALIST, Dec,, 1891, p. 1119. 
