blum: determination of aluminium 421 



stants of this group of 20 shunts (ranging from 0.1 ohm to 0.00025 

 ohm) at the Bureau of Standards are known to an accuracy 

 of 1 or 2 X 10 -7 second. With a frequency of 60 cycles and an 

 uncertainty of 2 X 10 ~ 7 second in the time-constant the phase 

 angle between the voltage and current is uncertain by about 

 15 seconds of arc. 



Further measurements were made on other types of shunt 

 and also on the effect of stray magnetic fields on the apparent 

 time-constants of the shunts. 



In the design of shunts for use with alternating currents it 

 appears that the liability to error can be minimized by so locat- 

 ing the potential leads that the inductive effects in them com- 

 pletely neutralize the inductance of the resistance material it- 

 self so that the shunt as a whole is strictly non-inductive. The 

 type in which the resistance material forms one or both of 

 two concentric tubes lends itself very readily to this form of 

 compensation. 



A study of the phase defects of mutual inductances of large 

 current capacity showed that this source of error was by no 

 means negligible and that it was particularly large in cases 

 where the secondary was wound in several layers. Errors from 

 this source can be minimized by making one of the windings, 

 preferably the secondary, in the form of a uniformly wound 

 closed toroid of fine wire, in which case the other winding may 

 be of large cross-section. 



CHEMISTRY. — The determination of aluminium as oxide. 1 

 William Blum, Bureau of Standards. 



From observations made with a hydrogen electrode and with 

 suitable indicators, it has been found that the precipitation of 

 aluminium hydroxide by ammonium hydroxide is complete when 

 [H + ] = 10 -6 5 to 10 -7 - 5 — points which are approximately de- 

 fined by the color changes of methyl red and of rosolic acid. 

 From a study of the various factors, the following conditions 

 are recommended for the determination of aluminium. To 



1 To appear in detail as Bur. Stds. Sci. Paper No. 2S6 (Bull. Bur. Stds., vol. 

 13). 1916. 



