ELECTROMOTIVE FORCES IX PYRIDINE 55 



tion a fractionating column was used and only that middle por- 

 tion which passed over between 77.9° and 78° (uncorr.) was 

 used. 



Methyl Alcohol. — Kahlbaunrs best grade of alcohol was fur- 

 ther purified in the same manner as the ethyl alcohol, except that 

 the treatment with quicklime was omitted. Only that distillate 

 passing over between 64.9° and 65.1° (uncorr.) was used. 



Pyridine. — The best grade of pyridine obtainable was allowed 

 to stand over fused potassium hydroxide for two weeks. It was 

 then decanted and distilled. That portion passing over between 

 115.3° and 115.4° was collected and preserved in dry glass-stop- 

 pered bottles, protected during distillation by a train of phos- 

 phorus pentoxide and calcium chloride tubes. Because of its 

 great absorptive power for water, extraordinary care was used 

 in handling the pyridine. 



Silver Nitrate. — Baker's ''Analyzed'"' silver nitrate was re- 

 crystallized by the rapid cooling of a hot saturated solution of 

 the salt in conductivity water. The crystals were filtered on a 

 Buchner funnel, washed with ice-cold conductivity water, sucked 

 dry, and then heated for several hours in a toluol bath at 109°. 

 The salt when thoroughly dry was kept in dark bottles further 

 protected by dark cloths, 



Potassium Chloride. — Baker's "Analyzed" potassium chloride 

 was further purified by precipitating a saturated solution by 

 hydrogen chloride gas. The precipiate was filtered on a Biich- 

 ner funnel, washed with conductivity water, heated to dryness 

 in an air bath at 110° and the crystals preserved in a desiccator 

 over phosphorus pentoxide. The salt was always strongly heated 

 before using. 



Mercury. — The mercury was repeatedly washed with dilute 

 nitric acid and the acid removed by repeated washing with con- 

 ductivity water. It was then distilled under reduced pressure 

 in a current of air. 



Calomel. — Kahlbaum's best grade of mercurous chloride was 

 repeatedly washed with a 0.10 N potassium chloride solution 

 after which it was preserved under a fresh sample of the same 

 solution in dark bottles. 



Solutions. — All solutions were prepared by direct weighing, 

 or by the suitable dilution of freshly prepared solutions. They 



