88 abstracts: physical chemistry 



PHYSICS. — Einige neue Doppelkompensatoren. Walter P, White. 

 Z. Instrumentenkunde, 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 outstanding small difference read directly by some de- 

 flection instrument. Such methods usually combine all the precision 

 of null methods with almost the quickness of straight deflection methods. 

 (2) The use of neutral C '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 sim- 

 ply using thin leaves of metal, adding blocks of the same metal in dial 

 switches. 



Various electrical arrangements for high-precision potentiometers, 

 suggested 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 chfferent from previous spht-circuit designs, and to a 

 new type, the "combination potentiometer" (features due to Hausrath, 

 Diesselhorst, White), which requires two batteries, but is otherwise re- 

 markably 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 quaii- 

 tities. A potentiometer with two sets of switches is especially eft'ective 

 in this respect, and practically does the work of two instruments. The 

 two sets of dials are controlled either by a master switch or by sliding 

 two sets of switch arms over a single set of central blocks. This latter 

 arrangement is easily secured in the "gridiron" potentiometer, by means 

 of a new and simple type of switch construction. 



Instruments now in use in the Geophysical Laboratory are described 

 which iUustrate the above types of design and construction. 



' W. P. W. 



PHYSICAL CHEMISTRY.— r/ie ternary system CaO-AWiSiO^. G- 

 A. Rankin; with optical study by Fred. E. Wright. Am. Jour- 

 Sci. (4), 39: 1-79. 1915. 

 The purpose of this investigation was to ascertain the stability rela- 

 tions in the ternary system CaO-Al203-Si02, not only from a purely sci- 



