CONDUCTIVITY OF SODIUM HYDROXIDE IN AQUEOUS SOLUTION. 259 



obtained in a clean condition by drawing it up into a short-nosed pipette (previously 

 warmed over a flame to prevent the sodium from solidifying in the tube), and then 

 squirting it into a porcelain basin containing melted paraffin wax. By allowing the 

 wax to solidify, the metal could be kept in a very convenient form, without under- 

 going any further oxidation. The most convenient method of weighing the metal 

 was to draw it up into a weighed pipette, in which the air had t>een freed from 

 oxygen and moisture by displacing it through a U-tube containing chips of metallic 

 sodium ; in this way it was possible to obtain a known weight of untarnished metal, 

 but in a form in which it could not readily be converted into the hydroxide. We were 

 therefore obliged to modify the method by transferring the melted sodium, before 

 weighing it, from the pipette into a bomb-shaped flask with short narrow neck, in 

 which the air had been freed from moisture and oxygen by suspending in it a 

 fragment of sodium during some hours before the flask was used. In taking the 

 sample of sodium from under the melted paraffin wax, purified air was blown through 

 the pipette to prevent the entrance of paraffin, and after the metal had been sucked up, 

 the outside of the pipette was wiped before allowing the metal to flow into the bomb. 



The flasks, which had a volume of about 200 cub. centims., were nearly filled with 

 the molten metal, closed with a small paraffined cork, allowed to cool, and weighed, 

 after momentarily loosening the cork in order to avoid a partial vacuum in the flask 

 during weighing. When required for use the metal was again melted, and poured, 

 at a temperature of about 150 C., into the silver cradle used in converting it into 

 hydroxide. When cold, the flask was again weighed, after momentarily loosening 

 the cork ; the difference gave the weight of sodium transferred minus the weight 

 of any oxygen absorbed by the metal in the flask during the operation. 



In checking the weight of sodium in the cradle, the metal was protected from the 

 air by a thin cover of silver foil, rapidly cooled by dipping the cradle into cold water, 

 and weighed as quickly as possible. The increase in weight of the cradle gave the 

 weight of metallic sodium plus that of any oxygen absorbed by the metal in the 

 transfer. The two weighings of the sodium differed, therefore, by an amount that was 

 dependent on the sum of the oxidations in the flask and in the cradle. Usually the 

 difference amounted to 10 milligrammes or 15 milligrammes, and only on one occasion 

 rose to 30 milligrammes in consequence of steam produced during the cooling of the 

 cradle obtaining access to the metal under one edge of the silver cover. As the 

 quantity of metal weighed was about 150 grammes, and the oxidation product was 

 not more than 15 milligrammes, the mean weight of the sodium was probably correct 

 within 1 part in 20,000. The error due to oxidation was certainly less than that 

 caused by uncertainty in the value of the atomic weight of the metal. 



It may be of interest to mention that in pouring the sodium from the bomb into 

 the cradle, the metal always flowed through a thin tube of oxide, reaching from the 

 mouth of the flask to the surface of the metal, and that even if the bomb had 

 contained a considerable quantity of oxidised metal, this could not have been poured 



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