82 REPORTS ON THE STATE OF SCIENCE. J 



It will be noted that the changes during the last three years are 

 very small. 



Silver Voltameter and Standard Cell. — Although the actions which 

 take place when a current passes through a solution of silver nitrate 

 as in a silver voltameter are now well understood, the effects of septa 

 — such as silk, filter paper, and porous porcelain — are by no means 

 clear, and experiments have, therefore, been made to decide whether 

 any septum at all should be used in a voltameter. Such experiments 

 were suggested at the Washington Meeting in 1910. The results of 

 the experiments made at the National Physical Laboratory indicate 

 that a septum of any kind is usually a source of trouble, and may 

 produce secondary reactions during the electrolysis which affect the 

 weight of the silver deposit. Fortunately, voltameters have been de- 

 signed which render a septum unnecessary, and these may be useful 

 not only in precise current measurements with the silver voltameter but 

 for the deposition of metals other than silver. 



The reproducibility and constancy of the Weston normal cell are 

 still being carefully examined. The chief anomaly is the hysteresis 

 effect mentioned in last year's Eeport : for this effect we have no 

 explanation although one is much needed, as probably it would enable 

 cells to be made so as to remain even more constant in e.m.f. than at 

 present. It is necessary to point out that while the effect is called a 

 hysteresis one, the e.m.f. does not lag behind the temperature. Briefly 

 put, with ascending temperatures the e.m.f. changes in close agree- 

 ment with the temperature — e.m.f. formula, but with descending tem- 

 peratures the e.m.f. changes too rapidly, corresponding to values at 

 temperatures lower than the temperature of the cell, by from 3° to 15°. 



The Committee had hoped to have made this their last Eeport, but 

 in view of the fact that the republication is not complete they ask for 

 reappointment, with Lord Rayleigh as Chairman and Dr. R. T. Glaze- 

 brook as Secretary. 



The Study of Isomorphous Sulphonic Derivatives of Benzene. — Report 

 of the Committee, consisting of Principal Miers (Chairman), and 

 Professors H. E. Armstrong (Secretary), W. J. Pope, and W. P. 

 Wynne. 



In the previous report it was stated that the crystallographic study of 

 the various derivatives of 1 : 4 di-derivatives of benzenesulphonic acid 

 containing halogens had been carried so far that it had been possible 

 to publish the results obtained in the case of twenty-nine such com- 

 pounds and that these results found a ready interpretation in the Bar- 

 low-Pope theory correlating molecular structure with crystalline form. 



During the past year considerable progress has been made with the 

 morphological study of other benzenesulphonic derivatives. Many 

 derivatives of benzenesulphonic acid have been examined crystallo- 

 graphically, including the anilide and several toluidides and xylidides. 



In addition, a number of the derivatives of benzenesulphonic acid 



