218 THOMAS COOKSEY. 



by caustic soda, phenol-phthalein being used as indicator. 

 There must of course be no carbonates, phosphates, silicates 

 or borates present. A definite quantity of neutral standard 

 barium chloride solution, more than sufficient to precipitate 

 all the sulphuric acid as barium sulphate, is now added, 

 and the proportion of spirit equal to half of the final total 

 liquid, together with a few drops of phenol-phthalein. Then 

 standard carbonate of soda is gradually run in with constant 

 stirring until a permanent pink colour is obtained. The 

 amount of barium chloride left in solution is given by the 

 number of cc. of carbonate of soda run in. The difference 

 between the latter figure and the amount of standard 

 chloride added gives directly the SO s in original liquid. 



"8989 SO 3 were taken. 15 cc. — Ba01 2 added to the boil- 



Example. — 5 cc. of a solution of NaaSO* containing 



N 



10 



ing test solution, the latter cooled and then after neutrali- 



\ 

 sation, titrated with — Na 2 0O 3 with gradual addition of 



N 

 25 cc. spirit of wine. 4*05 cc. — — Na 2 0O 3 were required. 



4*05 cc. - correction for spirit ('25) = 3*8 cc. 15-3*8 = 

 11*2 cc. Bad o solution required for precipitating the sul- 

 phuric acid. This is equivalent to *0445 S0 3 or *890f° S0 3 . 



In the estimation of sulphates in solution containing 

 magnesium or other metals it is advisable to precipitate 

 these by means of the mixture of hydrate and carbonate 

 of potash and work upon the filtrate. 



