274 



MR. W. R. BOUSFIELD AND DR. T M. LOWRY ON THE ELECTRICAL 



PART III. INFLUENCE OF TEMPERATURE ON THE DENSITY OF AQUEOUS 

 SOLUTIONS OF SODIUM HYDROXIDE. 



In order to be able to correct the conductivity measurements for changes of 

 concentration produced by alterations of temperature, it was necessary to know not 

 only the density of the solutions at 18C., but also the variation of density over the 

 whole range from C. to 100 C. The only statement that we have been able to 

 find with reference to the density of caustic soda at temperatures other than 15 C. 

 is a note by HAGER to the effect that the correction for temperature amounts to 

 0'00045 per degree centigrade from 50 per cent, to 40 per cent., 0'0004 from 

 29 per cent, to 30 per cent., O'OOOS from 29 per cent, to 20 per cent., and 0'0002 

 from 19 per cent, to 10 per cent. NaOH. The measurements of the variation of 

 density with temperature, originally undertaken on account of their bearing on the 



measurements of conductivity, proved to be of some interest 

 on their own account, and were therefore carried consider- 

 ably further than was originally intended. 



No special difficulty was encountered in measuring the 

 density at temperatures up to about 60 C., but at higher 

 temperatures the operation became somewhat troublesome, 

 and the measurements made at the boiling-point were found 

 to be subject to much larger errors than those made at 

 lower temperatures. For the mere purpose of correcting 

 the conductivities for the changes of concentration produced 

 by expansion it would have been sufficient to know the 

 density to three places of decimals, but the fourth place 

 was always determined, and, although the values obtained 

 at the boiling-point were occasionally erratic, we believe 

 that the smoothed values are accurate within a few units 

 in the fourth place. 



For this series of density measurements we employed a 

 type of density-tube very similar to that described by 

 Dr. PERKIN ('Trans. Chem. Soc.,' 1884, 45, p. 444), the actual 

 form being represented in fig. 4. The bulb is necessary in 

 order to allqw for the expansion of the liquid when deter- 

 mining the density at temperatures below that of the 

 atmosphere, but it is also useful at higher temperatures. 

 Only in the case of the most dilute solutions at tempera- 

 tures in the neighbourhood of the boiling-point was 



difficulty encountered from the distillation of moisture into the bulb. The tubes used 

 in some of the earlier experiments had a volume of only about 8 cub. centims., but 



Fig. 4. 



