142 CARNEGIE INSTITUTION OF WASHINGTON. 



(6) Das Studium der Mineralschmclzpunkte. Arthur L. Day. Fortschritte Min., 4, 115- 



160 (1914). 



A critical review of the work of recent years in the determination of the 

 melting temperatures of the minerals, in which an effort has been made to clear 

 up some of the confusion which now prevails in this field of research. Some 

 attention has been given to the applicability of the laws of solutions to the 

 change of state of minerals and to the criteria available for the definition and 

 experimental measurement of those changes of state which can be competently 

 studied with the methods and apparatus thus far developed. The effect of 

 disturbing factors, such as viscosity and inertia, which frequently intervene to 

 delay or prevent the establishment of equilibrium in the system, and so compel 

 the use of methods of approximation, has also been considered, together with 

 the effect of admixtures of minor mineral components in natural mineral types. 

 A sharp distinction is drawn between the characteristic properties of single 

 minerals and of groups of two or more in solid solution. The failure to recog- 

 nize and properly to appraise this distinction appears to have been the cause 

 of a considerable part of the confusion alluded to above. 



Following these general considerations, several pages are devoted to the 

 description of the apparatus now in use in the various laboratories for the 

 determination of mineral melting-points, together with the limitations en- 

 countered in its application to such studies and to the interpretation of the 

 results obtained with it. The effect of pressure upon the change of state in 

 minerals is also considered. 



The closing chapter contains a table of all the melting temperatures of record, 

 in which appropriate attention has been given to the chemical purity of the 

 specimen studied. 



(7) Einige neue Doppelkompensatoren. Walter P. White. Z. Instr., 34, 71-82; 107-113; 



142-151 (1914). 



This paper deals with the construction of potentiometers possessing the 

 high precision needed for accurate work with thermo-elements. Two general 

 features of value are: (1) The use of the partial deflection method, where the 

 quantity to be measured is largely compensated or balanced, and the out- 

 standing small difference read directly by some deflection instrument. Such 

 methods usually combine all the precision of null methods with almost the 

 quickness of straight deflection methods. (2) The use of neutral ("anti- 

 thermoelectric") contacts, especially in the switches. This renders it possible 

 to dispense with the very low contact resistance required in many existing 

 instruments, and also brings other advantages. Neutral contacts are easily 

 secured by simply using thin leaves of metal, adding blocks of the same metal 

 in dial switches. 



Various electrical arrangements for high-precision potentiometers, sug- 

 gested by Wolff, Waidner, Hausrath, Diesselhorst, Wenner, and the present 

 writer, are examined in detail. The preference is given to a "split-circuit" 

 potentiometer (embodying features due to Wenner and White) somewhat 

 different from previous split-circuit designs, and to a new type, the "combina- 

 tion potentiometer" (features due to Hausrath, Diesselhorst, White), which 

 requires two batteries, but is otherwise remarkably simple and free from 

 sources of error. 



One advantage of the potentiometer is the ease with which it can be adapted 

 to almost simultaneous readings of different electrical quantities. A poten- 

 tiometer with two sets of switches is especially effective in this respect, and 

 practically does the work of two instruments. The two sets of dials are con- 

 trolled either by a master switch or by sliding two sets of switch arms over a 



