374 



MESSRS. V. H. VELEY AND J. J. MANLET ON 



This method of standardisation, though tedious, probably eliminates the errors due 

 to a lag of the mercury thread to a greater degree than a more rapid process. It 

 was not thought necessary to apply the corrections for variations of atmospheric 

 pressure, or others adopted by the Bureau International, as the methods of deter- 

 mining the electric conductivity of a highly decomposable electrolyte are not 

 susceptible of such a degree of accuracy that such corrections would materially affect 

 the result. 



CALIBRATIONS OF ELECTROLYTIC CELL. 



In order to determine the mean cross-sectional area of this apparatus, two methods 

 were adopted : (i.) that described by BUNSEN (Gasometrische Methode), namely, by 

 pouring in equal volumes of mercury and reading the different levels .by a telescope, 

 the absolute volume of the measuring tube being subsequently ascertained by two 

 independent weighings of mercury at the temperature of the observation ; (ii.) by 

 pouring in from a funnel such a weight of mercury as would fill the burette for every 

 tenth graduation in cubic centimetres, the temperature being noted at the time. 

 The following results are given to illustrate the concordance obtained by the 

 two methods : 



TABLE II. 



The mean values were accepted as the true volumes. 



In order to measure the different lengths so as to deduce the cross sectional 

 areas, a pair of slide callipers was used, reading to '01 centim. and compared with a 

 standard metre. The highest and lowest value for the area within the limits of 

 observation were 4'4732 and 4'3839 sq. centims. respectively, so that the burette 

 was of a fairly uniform bore. 



KESISTANCE COILS. 



The resistance coils, supplied by Messrs. ELLIOT BROS., and marked as true ohms 

 at 16 were standardised by Mr. E. H. GRIFFITHS as against his coils, which had been 



