SCIENCE— ADVERTISEMENTS 



STANDARDS OF SELF 



IINDUCTAINCB 



Wound on Bakelite, these standards of Inductance are very con- 

 stant in form and do not change with age and use. Their time 

 constant is higher than usually offered. The wire used is finely 

 divided stranded wire, the individual strands of which are insu- 

 lated from each other. The construction renders these units ac- 

 curate, permanent and constant for all frequencies up to the tone 

 of radio frequencies. Supplied in various values from 1 milli- 

 henry to 1 henry. 



BROOKS' VARIABLE SELF AND MUTUAL INDUCTOR 



constructed in ranges up to 100 millihenrys. It is astatic, has a high time constant and prac- 

 tically a linear scale. The coils will dissipate a very considerable amount of heat. The moving 

 element is made of Bakelite. 



Bulletin No. 10 treats of " Secondary Standards of Inductance." 

 We will gladly mail you a copy. 



PYROLECTRIC INSTRUMENT CO. 



PYROMETRIC AND ELECTRICAL PRECrSION INSTRUMENTS 



636-640 EAST STATE STREET TRENTON, N. J. 



E. F. NORTHRUP, PRESIDENT AND TECHNICAL ADVISER 



HYDROGEN ION CONCENTRATIONS 



Acidity or alkalinity of a solution is easily de- 

 terminable without titration or indicator. 



Actual reaction is proportional to ionic con* 

 centration. 



Ionic concentration determines the electrical 

 conditions in a solution. 



Accurate information as to these conditions 

 may therefore be quickly obtained with appro- 

 priate electrical instruments. 



Experience and experiment show that the 



TYPE K POTENTIOMETER 



is an appropriate and highly convenient instrument for this purjHjse in laboratories of Chemistry, 

 Biology, Bacteriology and Physics. 



Catnlogue S70 tells about this instrument and its accessories 

 It awaits your request 



LEEDS AND NORTHRUP COMPANY 



ELECTRICAL MEASURING INSTRUMENTS 



4901 Stenton Avenue 



PHILADELPHIA 



