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



determine with special care the density of a series of solutions prepared from weighed 

 quantities of metallic sodium and to construct tables, by reference to which it was 

 possible to determine the percentage of sodium hydroxide in any solution with an 

 error amounting to little more than O'Ol per cent. The approximate values pre- 

 viously obtained by titration were then found to be incorrect to the extent of 0'2 per 

 cent, to 0'3'per cent. 



The quantitative conversion of sodium into sodium hydroxide was first undertaken 

 on a small scale in order to obtain a reliable standard alkali with which to compare 

 our unknown solutions by titration. But it soon became obvious that a closer 

 approach to purity and accurate standardisation would be attained if we could pre- 

 pare the whole of the material required for the investigation from weighed quantities 

 of metallic sodium. Quantities of sodium amounting to 50 grammes or 100 grammes 

 were therefore fused and poured into a weighed silver mug ; the mug (which we found 

 must be provided with silver baffle-plates to stop the spray) was placed in a shallow 

 dish of water, covered with a glass shade, and exposed to an atmosphere of steam 

 produced by gently warming the dish. The action proceeded quietly, and the rate at 

 which the sodium was acted upon was indicated by the escape of bubbles of hydrogen 

 from the glass shade. This arrangement proved, however, to be unstable, for 

 ultimately the metal, which had become covered with a layer of caustic soda, floated 

 to the top of the solution and caught fire in the steam, in one case after action had 

 proceeded during about 6 hours, and in a second case after about 30 hours. 



In order to avoid this result it would have been necessary to prolong the action 

 during many days. We were therefore led to devise forms of apparatus in which the 

 sodium was suspended in such a way that the caustic soda produced was allowed to 

 flow from the metal, thus maintaining a clean surface and uniform conditions 

 throughout the action. In this way we succeeded, for the first time, in converting a 

 bar of sodium directly into caustic soda, though the method involved the risk that 

 the sodium might become sufficiently heated to melt and flow, with disastrous 

 results, into the water or soda beneath. We were also able to carry out the 

 operation quantitatively, though in a somewhat risky manner, by suspending a 

 weighed quantity of metal in a silver cradle at the top of a large platinum test-tube 

 over a quantity of water which was distilled on to the metal, under reduced pressure, 

 by gently warming the tube. This method was completely successful, but was some- 

 what tedious in the later stages, owing to the great reduction of vapour-pressure 

 caused by the dissolution of caustic soda in the water. This difficulty was overcome 

 by distilling the water into the platinum tube from a flask, of which the neck was 

 drawn out and bent so as to enter the cover of the tube ; in this form the apparatus 

 was used for preparing some two litres of standard 50-per cent solution. 



Some of the details of the method may now be described. 



(1.) Purifying and Weighing the Sodium. In order to get rid of oxide and other 

 superficial impurities, the sodium was melted under xylene or paraffin oil, and was 



