312 Gooch and Hill — Purification of Barium Sulphate. 



was added, and then from 2 cm3 to 5 cm3 of sulphuric acid. The 

 water and excess of sulphuric acid were evaporated off by 

 directing a small flame from the blast lamp nearly vertic- 

 ally downward upon the liquid. The evaporation required 

 about fifteen minutes. The results obtained upon weighing 

 the crucible and barium sulphate were satisfactory in three 

 cases out of five, but in the other two cases there was loss. 

 To prevent this a cone of fine platinum gauze was fitted into 

 the mouth of the crucible and the flame was directed against the 

 point of the cone. This prevented the loss by spattering. The 

 point of the cone must not be allowed to dip into the liquid, 

 for otherwise some of the barium sulphate will be left above 

 the gauze and may be blown away. The gauze was weighed 

 with the crucible and cover each time, so that if any of the 

 barium sulphate should spatter against the gauze its weight 

 would not be lost. The results where the gauze was used were 

 more consistently satisfactory and we felt encouraged to carry 

 on further experiments using the gauze, but not without it. 

 The average time required for completing an evaporation in 

 these and subsequent experiments where the gauze was used 

 was about one half hour. Table I gives the results of the 

 experiments in which the naked flame was directed upon the 

 solution, Table II those of the experiments in which the gauze 

 was interposed. 



wt. 





Table 1. 





of BaCl 2 . 2H 2 









taken 



BaS0 4 found 



BaS0 4 by theory 



Error 



grm. 



grm. 



grm. 



grm. 



0-4996 



0-4774 



0-4773 



+ 0-0001 



0-4996 



0-47V4 



0-4773 



+ 0-0001 



0-4996 



0-4747 



0-4773 



— 0-0026 



0-4996 



0-4773 



0-4773 



o-oooo 



0*4996 



0-4765 



04773 



— 0-0008 





Table II. 





of Ba01 2 . 2H 2 









taken 



BaS0 4 found 



BaS0 4 by theory 



Error 



grm. 



grm. 



grm. 



grm. 



0-4996 



0-4770 



04773 



— 0-0003* 



0-4996 



0-4777 



0-4773 



+ 0-0004 



0-4996 



0-4768 



0-4773 



— 0-0005 



0-4996 



0-4768 



0-4773 



— 0-0005 



04996 



0-4774 



0-4773 



+ 0-0001 



04996 



0-4776 



0-4773 



+ 0-0003 



* The tip of the gauze dipped into the liquid. 



For use in the subsequent experiments a solution to contain 

 approximately 0*5 grm. of BaCl 2 .2H 2 in 50 cm3 was prepared 



