POTASH. 101 



The lime absorbs the chlorine as soon as it comes in contact 

 with the solution ; the supernatant water is immediately de- 

 canted and the application of chlorine liquor repeated, as 

 above, several times. By exposure to a gentle heat for a 

 short period, the moisture is driven off, and pure chloride of 

 lime remains. 



Chlorate of Potassa. — Calvert's process (Comptes Rendus, 

 1850) is to pass a current of chlorine gas through a hot (122°) 

 mixture of 5|-6 equivalents of burnt lime and 1 equiv. caustic 

 potassa in water. Chloride of calcium and chlorate of potassa 

 are the products. When the solution is saturated with the 

 gas, it is to be filtered, evaporated to dryness, redissolved in 

 boiling water, and allowed to cool. The use of lime saves the 

 great loss of potassa by other processes, 22 pts. of chlorate 

 being obtained from every 10 pts. of potassa employed. 



4. Potash is obtained by lixiviating the ashes of trees, 

 evaporating the solution to dryness and calcining the residue. 

 When purer, but more carbonated, it is termed pearlash. 



New Source of Potash. — H. Wurtz has suggested a method 

 of decomposing green sand, with the view of gaining its potash, 

 by fusing it with chloride of calcium. See Amer. Journ. 2d 

 ser. X. 326, where many experiments are detailed having the 

 same object in view. 



Potash tested for Soda. — Pagenstecher's method is as fol- 

 lows (Mittheil. d. Naturf. Gesellsch. in Bern, No. 65). It is 

 based on the fact that a saturated solution of sulphate of 

 potassa can dissolve large quantities of sulphate of soda. 

 About half an ounce of the potash to be tested is poured over 

 with water, treated with sulphuric acid until it has an acid re- 

 action, evaporated to dryness, ignited, and weighed. The pow- 

 dered saline mass is then treated with 6 times its weight of a 

 concentrated solution of sulphate of potassa, stirred, allowed to 

 settle, and the clear liquor drawn off from the sediment by a 

 siphon. After being again treated with a like quantity of 

 the sulphate of potassa solution, the residue is thrown on a 

 balanced filter (the funnel covered with a glass plate during 

 filtering to avoid evaporation), and when the last drops have 

 j2 



