DETERMINATION OF ALKALIES IN MINERALS. 211 



latter. The annoyance attendant upon this exact precipitation 

 is familiar to all who may have had occasion to make the trial. 



32. Instead of the chloride of barium the acetate of lead is 

 used; a solution of this salt is poured in excess upon the so- 

 lution of sulphates ; warming the latter slightly, the sulphate 

 of lead readily separates; the whole can be immediately thrown 

 on a filter and washed. A drop or two of the acetate of lead 

 should be added to the filtrate to insure there being an excess 

 of the lead-salt. 



33. The filtrate is then warmed and sulpureted hydrogen 

 added ; care must be taken to see that there is an excess of sul- 

 phureted hydrogen, a test most readily performed by means 

 of a piece of lead-paper. The liquid is thrown on a filter to 

 separate the sulphuret of lead ; the filtrate containing the 

 alkalies as acetates is evaporated, and when nearly dry an 

 excess of hydrochloric acid is added, and the whole evaporated 

 to dryness over a water-bath, and finally heated to above 500°. 

 A hot solution of the chloride of lead can be used instead of 

 the acetate, rendering the addition of hydrochloric acid un- 

 necessary. 



34. It needs but little experience to convince one of the 

 superiority of this method over that by the chloride of barium 

 for converting the sulphates into the chlorides, its principal 

 recommendation being the indifference with which an excess 

 of the lead-salt can be added to precipitate the sulphuric acid, 

 and the subsequent facility with which that excess of lead can 

 be got rid of. It may be well to state that experiments were 

 made to prove the perfect precipitation of the sulphuric acid 

 from the sulphates of the alkalies by the salts of lead, and it is 

 only after numerous comparative results that it is now recom- 

 mended. 



TO DISTINGUISH THE ALKALIES FROM EACH OTHER WHEN MlXED. 



35. To distinguish potash, soda, and lithia when mixed is 

 attended with more or less difficulty, according to the propor- 

 tions in which they are mixed; of the three, potash is the most 

 easily recognized, next in order is soda, and lastly lithia; the 

 presence of which, mixed in small amount with proportionally 

 large quantities of the other alkalies, it is almost impossible to 

 decide on with any accuracy without direct separation. 



