SULPHATE OF POTASSA AND MAGNESIA. 19 



5. By distilling the weighed salt with a moderately 

 concentrated solution of soda, the ammonia is evolved, 

 and may be combined with hydrochloric acid. This 

 is best effected in a small flask furnished with a fun- 

 nel-tube by which the solution of soda is introduced, 

 and a long condensing-tube, the end of which dips 

 into moderately-strong hydrochloric acid. The liquid 

 is retained in ebullition until one-half has distilled 

 over. The hydrochloric solution is carefully evapo- 

 rated to dryness in a weighed dish, over a water-bath, 

 and the -residue of chloride of ammonium weighed ; or 

 it may be converted into ammonio-chloride of plati- 

 num, which is then treated as above. 



After determining the soda, the ammonia, and the 

 sulphuric acid, the quantity of the water may be ascer- 

 tained by difference. It may also be controlled by 

 mixing a weighed portion of the powdered salt, in a 

 platinum crucible, with an excess of freshly-burnt 

 lime, free from water and carbonic acid ; the mixture 

 is covered with a layer of lime, the whole weighed, 

 and very strongly ignited over a gas burner. The 

 loss of weight represents the joint amount of the am- 

 monia and water. 



6. SULPHATE OF POTASSA AND MAGNESIA.* 

 KO, S0 3 ; MgO, S0 3 H-6HO. 



This salt loses all its water at 133. The sulphuric 

 acid is determined by precipitation by chloride of 

 barium (see No. 3). 



For the estimation of the magnesia, another weighed 

 quantity of the salt is dissolved in water, mixed with 



* This salt 'is easily obtained in crystals, by mixing a boiling 

 saturated solution of 1 part of sulphate of potassa, with a saturated 

 solution of 1^ part of sulphate of magnesia. 



