206 QUANTITATIVE ANALYSIS. 



i 

 flame, and, after a few minutes, add cautiously 10-15 cc. of 



barium chloride solution which has been previously heated. 

 Then let stand, preferably till next day, so that the barium 

 sulphate may settle completely. If this does not take place, 

 heat the beaker on the water-bath until the barium sulphate 

 has settled and the fluid appears perfectly clear. Filter, after 

 the heating on the water-bath, through a small, ash-free, close 

 filter of 9 cm. diameter, and transfer the precipitate completely 

 to the filter with the aid of a glass rod having a piece of rub- 

 ber tubing on its end. The filtrate must be perfectly clear. 

 If it is not, it is made so by pouring it repeatedly back on the 

 filter. Test the clear filtrate by means of dilute sulphuric 

 acid, to determine if sufficient barium chloride has been 

 added, then wash the precipitate with warm water until a 

 portion of the last wash-water is no longer rendered turbid 

 with silver nitrate solution, pour the filter full of absolute 

 alcohol once or twice to remove coloring matters (indigo 

 blue and red) and to dry, and then once full of ether. To 

 determine the quantity of the barium sulphate thus obtained 

 place the filter, which is perfectly dry after some minutes, 

 together with the precipitate, in a weighed platinum cruci- 

 ble, heat gently at first, with the cover partly on, and then 

 more strongly for about five minutes or longer (with thick 

 paper), at any rate until the contents of the crucible appear 

 perfectly white, let cool and weigh. The difference in weight 

 gives the quantity of barium sulphate. This weight mul- 



98 08 

 tiplied by O ^~T, =0.4201 gives the quantity of sulphuric acid, 



and multiplied by ^^-^ = 0.3^2^3 the quantity of sulphuric 



,ZOG.T:O 



anhydride. 



