Gooch and Hill — Purification of Barium Sulphate. 311 



Art. XXVIII. — The Purification of Barium Sulphate precip- 

 itated in the Determination of Barium ; by F. A. Gooch 

 and D. IT. Hill. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — ccxlii.] 



When in the determination of barium as the sulphate the 

 precipitation is made in the presence of alkali salts, consider- 

 able errors — sometimes as much as 20 milligrams in one half 

 gram of precipitate — may be occasioned by occlusion of the 

 foreign salts. It has been found that, upon dissolving the pre- 

 cipitate of barium sulphate in concentrated sulphuric acid and 

 evaporating to dryness, the barium sulphate crystallizes in more 

 or less coarsely granular crystals which may be washed free 

 from the other sulphates.* The evaporation must be made with 



special care in order to avoid loss by spattering and creeping. 

 With a ring burner this process takes several hours, but with a 

 Hempel burner an evaporation can be made safely in about 

 one half hour. The present object has been to find out whether 

 the evaporation cannot be safely made by directing the name 

 of a blast lamp down upon the surface of the liquid, thus sub- 

 stituting for the Hempel burner a piece of apparatus that is in 

 more general use. 



Preliminary experiments to determine whether an evapo- 

 ration without loss of barium sulphate could be made with the 

 blast lamp were carried out in the following manner : Crystal- 

 lized barium chloride (C.P.) was powdered and bottled without 

 drying, and the water content determined by gentle ignition. 

 Of this salt portions of 0*5000 grm. each were weighed into a 

 previously weighed platinum crucible. About 5 cm3 of water 



* Mar, this Journal, xli, 295, 1891 . 



