Processes for Potassium. 63 



my former paper, be attended to. The heat should not be carried 

 beyond full redness, otherwise it will carry over a portion of carbon, 

 rendering the metal impure ; whenever this occurs, the process is at 

 an end ; for the tube is clogged, and all the metal, subsequently subli- 

 mated, is condensed over the carbonaceous deposit, requiring a full 

 red heat to separate it. Hence, when we redistil, care is necessary 

 as to the proper temperature. If the tube should chance to be clog- 

 ged, from too high heat, the only remedy is to remove the apparatus 

 from the fire, unscrew the tube from the receiver, and, when cool 

 enough, detach the contents, according to previous directions, and 

 put them into the receiver. Clean the tube by washing and wiping 

 till perfectly dry ; — if any oxide of iron remain on the inside, remove 

 it by friction with sand and soap, and when the iron is clean and 

 bright, replace the tube, insert the apparatus into the furnace, and 

 distil as directed. It was stated in my former paper, that the first 

 operation, or distillation, is knovi^n to be going on well when gas is 

 uniformly evolved 5 if this is suddenly diminished, the retort is cool- 

 ed by throwing in fresh materials fused by the heat, or the tube may be- 

 clogged. But if the gas gradually diminishes, it was supposed that the 

 process must be nearly ended, that is, that the potassa was exhausted. 

 This however is not always the case ; these appearances may arise 

 from the fusion of the retorts, as occurred to me in two instances ; 

 the hole at first being very small, but gradually enlarging so as to 

 emit the vapor of the metal as fast as sublimed. There is, however, 

 one sure indication, that the potassa in the retort is exhausted, that is 

 by withdrawing a few of the card-teeth or iron turnings ; if there be 

 a supply of potassa, they vi'ill be bright and clean, but if it is exhaust- 

 ed they will be blackened by oxidation. 



If an excess of carbon have been used in the operation, though 

 the heat required is less, I have often thought the product of metal 

 was greater ; at any rate it is more impure, requiring a second redis- 

 tillation before all the carbon is separated. That the carbon has not 

 been removed, is ascertained by the appearance of the naphtha in which 

 it is preserved, which after standing some days becomes of a light or 

 dark brown, according to the proproiion of carbon contained. This 

 effect seems to arise from the slight oxidation of the metal, by which 

 the carbon, in a state of minute division, is set free and suspended 

 in the liquid. It is stated, in a note to the third American edition of 

 Turner's Chemistry, that potassium may be effectually preserved in 

 the essential oil of copaiva, on which authority I mentioned that article 

 in my former paper. Since that, however, I have made experiments, 



