238 QUANTITATIVE ANALYSIS. 



Only barium chloride, together with some salts present hi 

 solution, passes through the filter, while the insoluble barium 

 carbonate remains behind. Wash the dish with hot water, 

 pour into the filter which was previously used, and wash 

 until all the barium chloride has been completely washed out 

 of the filter. By working carefully this may be accom- 

 plished without increasing the volume of the filtrate and the 

 wash- water to more than 50 to 60 cc. We may also con- 

 tinue the washing somewiiat longer and then cautiously 

 evaporate to 50 cc. In any case the last wash- water which 

 is thought to be free from barium chloride is collected by 

 itself and tested with silver nitrate and nitric acid. 1 The 

 filtrate and the wash-water contain all the hydrochloric 

 acid of the gastric juice combined with barium. The amount 

 of barium is hence a direct measure of the amount of hydro- 

 chloric acid. 



To determine the amoun,t of barium, acidify the filtrate 

 and wash-water with a few drops of hydrochloric acid, heat 

 in a beaker on the wire gauze until boiling begins, add about 

 4 to 5 cc. of dilute sulphuric acid (also previously heated), 

 then heat further on the water-bath until the barium sul- 

 phate settles, leaving a clear solution. Filter through a 

 close, ash-free filter 2 of about 9 cm. diameter, transfer the 

 precipitate completely to the filter the filtrate must be 

 perfectly clear; if it is not, it must be again passed through 

 the same filter and wash until a portion of the wash-water 

 is no longer rendered turbid by silver nitrate solution or by 

 barium chloride solution. Then fill the filter once with 



1 The original direction, to wash until a portion of the wash-water is 

 no longer made turbid with sulphuric acid, is not to be adhered to, since 

 such a point, in consequence of the slight solubility of the barium car- 

 bonate in water, is not to be attained. Too long-continued washing may 

 therefore also lead to a plus error. 



a Suitable filter-papers are the No. 590 of Schleicher and Schiill, and 

 the ash-free baryta filter-papers Nos. 400 and 412 of Dreverhoff in Dresden. 



