8 John White 



To obtain the crystals in a form suitable for analysis, they 

 were collected on a Witt filter and washed by the aid of the 

 pump with a wash liquid prepared by mixing together in 

 approximately equal volumes dry ethyl "acetate and strong 

 alcohol in which a small quantity of sodium acetate had been ' 

 dissolved; the latter was found to be necessary to prevent 

 (drive back) the dissociation of the double salt, which invar- 

 iably happens as soon as the excess of sodium acetate has been 

 washed out. After washing, the crystals were immediately 

 transferred to a watch glass, placed in a vacuum desiccator, 

 and dried in a vacuum over strong sulfuric acid, which 

 requires onl}^ a short time. The yellowish tint can be removed 

 by shaking them up in a stoppered flask with dry ethyl acetate, 

 letting them stand for twenty-four hours or longer. The 

 crystals become somewhat opaque and white, while the ethyl 

 acetate assumes a yellowish hue. Comparative analysis made 

 with the slightly yellow and the washed crystals shows that 

 there was practically no difference in theni ; the color is prob- 

 ably due to a very slight superficial decomposition with forma- 

 tion of lead iodid. 



The iodin in the salt was determined by dissolving with the 

 aid of heat in water, slightly acidulated with nitric acid, and 

 then precipitating as silver iodid. To estimate the lead and 

 sodium, the solution in very weakly acidulated water was 

 saturated with hydrogen sulfid, thus precipitating the lead. 

 The lead sulfid was collected on a filter, dried, the paper 

 burned, and the sulfid oxydized in a porcelain crucible by 

 fuming nitric acid, the excess of acid evaporated off, a drop 

 of strong sulfuric acid added, evaporated over a small flame, 

 ignited gently, and weighed as sulfate. The filtrate from the 

 lead sulfid was evaporated in a platinum dish on the water 

 bath, filtered to remove the trace of lead sulfid, transferred 

 to a weighed platinum crucible, evaporated to dryness, a drop 

 or two of strong sulfuric acid added, and evaporated over a 

 small flame, after addition of ammonium carbonate. The 

 sodium was eventually weighed as the sulfate. The results 

 proved very satisfactory. The carbon and hydrogen were 



314 



