350 Scientific Intelligence. 



as well asTiore accurate to employ short swings of from about 

 1/4 to one or two divisions on each side of the center, such as the 

 balance gives very easily. h. l. w. 



5. Volumetric Analysis for Students of Pharmaceutical and 

 General Chemistry; by Charles H. Hampshire. 12mo, pp. 

 124. Philadelphia, 1921 (P. Blakiston's Son & Co. Price, $1.45 

 net). — This little book, which is of British origin, now appears in 

 a third edition. It presents a very good general introductory 

 course including the principal standard methods. The exercises 

 for practice are numerous, systematically arranged and clearly 

 presented. More than a single method is frequently applied for 

 a determination ; for instance, three methods are given for find- 

 ing the strength of bleaching-powder. Sections of the book in 

 small type give a large number of determinations based on the 

 requirements of the British Pharmacopoeia. h. l. w. 



6. Etalon Interferometer. — The homogeneity and reproduci- 

 bility of the lines in the spectra of argon, krypton, and xenon 

 make them useful as secondary standards of wave lengths. 

 Scientific Paper 414 of the Bureau of Standards contains the most 

 recent measurement of the stronger lines of these spectra which 

 are probably correct to one part in several million. The elegance 

 and precision of the interferometer methods for wave length 

 comparisons are demonstrated by the close agreement between 

 values obtained by different observers and also by the constant 

 frequency dift'erences of many of the lines belonging to combina- 

 tion series. 



This publication is now ready for distribution by the Depart- 

 ment of Commerce as is also the table of contents to Vol. 16 of the 

 above mentioned series of papers. f. e. b. 



7. The Wehnelt Interrupter. — The form of electrolytic inter- 

 rupter using sulphuric acid as described by Wehnelt is subject to 

 several faults which seriously impair its operation as a current 

 break for an induction coil. The liquid often reaches the boiling 

 point when the current ceases entirely. The platinum wire 

 slowly disintegrates when used as anode and is likely to melt 

 when it functions as cathode. Also the fumes and spraying of 

 the acid are very objectionable. 



A new form devised by F. H. Newman gives much more sat- 

 isfactory results. For the electrolyte he uses ammonium phos- 

 phate in an aluminum vessel which serves as cathode. The anode 

 as usual is a platinum rod which may be protruded from a por- 

 celain sheath. On account of the lower current densitj^ the 

 cumulative heating does not reach a point where it stops the 

 operation of the break. The latter functions steadily even at 

 90° C. The current passes practically only in one direction so 

 that the apparatus may be introduced into an alternating current 

 circuit. 



