100 REPORTS ON INVESTIGATIONS AND PROJECTS. 



(15) The calibration of copper-constantan thermoelements. Walter P. White, H. C. 



Dickinson, and E. F. Mueller. Phys. Rev., 31, 159. 1910. 



Through the courtesy of the Director of the U. S. Bureau of Standards, 

 some thermo-elements from the Geophysical Laboratory were calibrated at 

 the Bureau and afforded a favorable opportunity for the study of the general 

 properties of these thermo-elements in direct comparison with resistance- 

 thermometers for low-temperature measurements of great precision. The 

 result of the calibration is given here. Some of the advantages and disad- 

 vantages of thermo-elements for this work have been outlined in the preced- 

 ing abstract (14). 



A pair of copper-constantan thermo-elements for use in calorimetric work 

 was calibrated by comparison with standard resistance thermometers to an 

 accuracy of 0.004 . It is probable that the accuracy of the calibration could 

 be considerably increased if need be. A cubic equation represents the rela- 

 tion between the temperature and electromotive force, in the interval o° to 

 ioo°, with an accuracy of 0.005 or better. The resistance thermometers 

 were read to 0.001 and the thermo-element to 0.003 , the difference in sen- 

 sitiveness being practically due to the difference in the galvanometer used. 



(16) The thermal dissociation of calcium carbonate. John Johnston. Journ. Am. Chem. 



Soc, 32, 938- 1910. 



In all previous measurements of the equilibrium pressure of the reaction 

 CaC0 3 ^~^ CaO -f- C0 2 , the errors have been due mainly to a lack of defi- 

 niteness in the temperature of the reacting system. In the experiments de- 

 scribed in this paper, which extend over a temperature range of about 300 , 

 this difficulty was obviated by the use of an improved form of apparatus, 

 which, with a total vapor space of not more than 5 cc, required only 0.1 

 gram of substance. With this arrangement, the temperature of the charge 

 was easily kept uniform, and was determined with an accuracy of ± 2° at 

 900 C. The results of these measurements are well reproduced by the 

 equation : 



\ogp = — 9340/T-l- 1.1 log T — 0.0012 T -f- 8.882 



where p is the equilibrium pressure (expressed in millimeters of mercury) 

 at the absolute temperature T. The pressure reaches one atmosphere at 

 898 C. The above formula was deduced from thermodynamic considera- 

 tions ; accordingly it may be used with some confidence for obtaining the 

 pressures corresponding to temperatures above 900 C, the extrapolated 

 values being more reasonable than those obtained by the use of the formulas 

 previously proposed by others. 



(17) A new occurrence of plumbojarosite. W. F. Hillebrand and Fred. Eugene 



Wright. Am. Journ. Sci. (4), 30, 191. 1910. 



A brief description of the crystals of this mineral from American Fork, 

 Utah. Its observed optical and chemical properties agree well with those of 

 plumbojarosite from Cooks Peak, New Mexico. 



(18) The transmission of light through transparent inactive crystal plates. Fred. 



Eugene Wright. Am. Journ. Sci. (In press.) 



An investigation into the influence of the boundary surfaces of inactive 

 transparent crystal plates on transmitted light-waves. The problem of re- 

 fraction and reflection of light on crystal plates was first solved successfully 

 in a general way in 1835 by F. E. Neumann in Germany and by J. MacCul- 



