16 ROCHELLE SALT. 



paper. When perfectly washed, it is dried, separated 

 as much as possible from the filter, the latter being 

 completely incinerated, and its ashes added to the pre- 

 cipitate, which is then ignited and weighed. 100 parts 

 of sulphate of baryta contain 34.29 of sulphuric acid, 

 or 13.71 of sulphur. The amount of soda is deter- 

 mined by difference. 



4. TARTRATE OF POTASSA AND SODA.* 

 Seignette-salt ; Eochelle-salt, (K0 ; NaO, T + 8 HO). 



The estimation of the water requires the cautious 

 application of heat for a long period. The salt fuses 

 even below 100, and enters into ebullition at 120, 

 but does not lose the whole of its water till heated to 

 215. 



To determine the bases, the salt is ignited, the alka- 

 lies dissolved out of the carbonaceous mass by dilute 

 hydrochloric acid, and the filtered solution evaporated 

 to dryness; the mixed chlorides are heated to dull 

 redness in a covered platinum crucible and weighed. 

 They are then dissolved in a little water, and the solu- 

 tion mixed with a moderately concentrated solution 

 of bichloride of platinum. The solution, with the sus- 

 pended precipitate, is evaporated to dryness on the 

 water-bath, the dry mass digested for some time with 

 alcohol, and the potassio-chloride of platinum col- 

 lected upon a filter which has been dried at 100, 

 and weighed. The filtrate, which contains the sodio- 

 chloride of platinum, must still have a distinct yellow 

 color. The platinum-salt is washed with alcohol, 



* Prepared by saturating a hot mixture of water and powdered 

 tartar with carbonate of soda, filtering, and crystallizing. 



