I06 REPORTS ON INVESTIGATIONS AND PROJECTS. 



(26) Quartz and fluorite as standards of density and refractive index. H. E. Merwin. 



Am. J. Sci. (4), 31, 429- 191 1- 

 For checking the accuracy and adjustment of instruments, easily available 

 standards are desirable. Standards of density correct to ± o.ooi and of 

 refractive index correct to ±: o.oooi are particularly useful to mineralogists. 

 Quartz and fluorite in clear colorless varieties appear to be the only minerals 

 of wide distribution that are uniform enough in composition to serve as 

 standards of this accuracy. Therefore the density and refractive index of 

 these minerals at 20° have been investigated. The determined density of 

 quartz from 12 localities is 2.6495 ± o.ooi ; of fluorite from 9 localities, 

 3.180 ±0.001. By these standards the Westphal balance may be tested. 

 The refractive index, WNa, of 5 quartzes, determined by means of the spec- 

 trometer and a standardized total refractometer, was found to be 1.54425 d= 

 0.0001; of fluorite, the value found was 1.43385 ± o.oooi. These values 

 agree sufficiently closely with those of other observers. 



(27) A method for determining the density of certain solids by means of Rohrbach's 



solution having a standard refractive index. H. E. Merwin. Am. J. Sci. 

 (4)31,425. 1911. 



By means of Rohrbach's solution, so prepared that the relation of its 

 density to its refractive index is known, the density of suitable solids between 

 2 and 3.5 can be determined rapidly and accurately on the total refractom- 

 eter by finding the refractive index of the solution while fragments of the 

 solid are suspended in it. The solution saturated with mercuric iodide at 20° 

 and at the density of ordinary ortho rhombic sulphur (2.07) has, for concen- 

 trations between 2.25 and 3.4, the relation ^ = 5.39^ — 6.0865, where d is 

 the density and 11 the refractive index. 



(28) A micrometer ocular with coordinate scale. Fred. Eugene Wright. J. Wash. 



Acad. Sci., 1, 60. 191 1. 



This new eye-piece consists essentially of a hollow brass cylinder which 

 fits into the microscope tube as an ordinary eye-piece, and serves as support 

 for a positive Ramsden ocular in the focal plane of which a finely divided o.i 

 mm. coordinate scale is placed. The ocular has been designed to serve three 

 purposes: (i) that of an ordinary micrometer eye-piece; (2) that of a 

 coordinate ocular for the geometrical analysis of rock thin sections, either 

 by the Rosiwal method or by the less accurate method of percentage areas ; 

 and (3) for the measurement of the optic axial angle of mineral plates in the 

 thin section, provided that at least one optic axis appears in the field of view. 



(29) Neuere Verbesserungen am petrographischen Mikroskop. Fred. Eugene Wright. 



Centr. Min., 555. 191 1. 



A brief discussion of the principles underlying the design, construction, 

 and adjustment of the petrographic microscope, together with a description 

 of recent improvements which have been made for the purpose of facilitating 

 the accurate measurement of the optical properties of fine-grained mineral 

 preparations, especially of artificial silicate melts. 



(30) Recent progress in Calorimetry. Walter P. White. 



I. The real vs. the supposed errors. Met. Chem. Eng., ix, 202. 191 1. 

 II. Details of apparatus and method. Met. Chem. Eng. ix, 296. 191 1. 

 III. Temperature measurement and corrections. Met. Chem. Eng., ix, 449. 1911. 



A brief review of recent progress in calorimetry for the use of engineers. 



