300 abstracts: engineering 



The Diphenylamine test for nitrates and the Iodide test for nitrites 

 were found to be wholly unreliable. It was found impossible to es- 

 timate nitrates in the presence of nitrites; the "Hydrostrychnique" 

 and the Brucine test reacted with nitrites in the same way as with 

 nitrates so that the results of these methods must be expressed in 

 terms of nitrates and nitrites. In the absence of iron, the "Hydro- 

 strychnique" or a modification of the Brucine test is recommended. 

 In the presence of iron, only the original Brucine test may be used. 



It was found that nitrites could be estimated in the presence of 

 nitrates and best by the Dimethylaniline method. L- B. S. 



PHYSICAL CHEMISTRY. — Hydrogen ion concentration in dry cells. 

 H. D. Holler and L. M. Ritchie. Bur. Standards Sci. Paper 

 364. Pp. lo, figs. 3. 1920. 



The potentials of electrodes consisting of mixtures of Acheson graphite 

 with three different manganese ores and a chemically prepared oxide 

 were measured in ammonium chloride solutions of different hydrogen 

 ion concentrations. The potential of the electrodes containing the 

 ores was found to be a logarithmic function of the hydrogen ion con- 

 centration, while the potential of electrodes containing the chemically 

 prepared oxide was found to be independent of hydrogen ion concentra- 

 tion. The potential of the ores was found to decrease in acid solution 

 and to increase in alkaline solutions. The relation found between 

 the potential of the manganese dioxide electrode and hydrogen ion 

 concentration, explains variations in open-circuit voltage of dry cells 

 containing a given ore, and also accounts for a portion, at least, of the 

 polarization of dr\- cells on discharge. H. D. H. 



ENGINEERING. — The accuracy of commercial electrical measure- 

 ments. H. B. Brooks. Advance Paper, Trans. A. I. E- E. 

 1920. Presented February 20, 1920. 



The paper discusses the accuracy required in commercial electrical 

 measurements, and the means of obtaining it, namely, proper choice, 

 installation, use, and maintenance of instruments. The effect of room 

 temperature change is discussed in detail, with special attention to fea- 

 tures and methods of design which will minimize this effect. The effect 

 of stray magnetic field is discussed from the same viewpoint. 



Considering electrodynamic instruments as reducible to a pair of coils 

 capable of relative motion, it is shown experimentally that the errors 



