78 § 59. BASES AND ACIDS WITH REAGENTS. 



the sulphuric acid is expelled ; digest the residue with 

 hydrochloric acid; it should be dissolved completely, 

 although, if calcium is present, considerable time may bo 

 required. If the solution is not complete, the insoluble 

 l^art should be treated again with ammonic fluoride. 



SULPHURIC ACID. II2SO4. 



59. The sulphates of lead, barium, and calcium, are in- 

 soluble, or difficultly soluble, in water and dilute acids ; 

 the last of the three is much the most soluble. 



Reactions* — Sulphuric acid and solutions of sulphates 

 give a finely pulverulent i)recipitate, BaSO^, with baric, 

 chloride, insoluble in water or dilute acids ; the reaction 

 is very delicate. 



Quantitative estimation. — This acid is always de- 

 termined as baric sulphate, BaSO^. Heat the slightly 

 acid solution nearly to boiling, and add a hot solution 

 of baric chloride as long as a precipitate is formed ; 

 let the mixture stand until the precipitate settles, and 

 wash the latter by decantation, until the washings 

 give no reaction for barium with sulphuric acid ; then 

 pour 40 or 50 c.c. of the solution of cupric acetate 

 (§ 9) over the precipitate in the beaker, add some water 

 and so much acetic acid that, after digestion for 10 

 or 15 minutes at a temperature very near to boiling, no 

 basic cupric salt separates from the solution ; if any does 

 appear, dissolve it by adding mere acetic acid ; stir the 

 mixture constantly during the digestion. Filter, wash 

 the precipitate with hot water, and, if the filter is still 

 colored blue, moisten it with a little dilute hydrochloric 

 acid and wash with more water, until the washings give 

 no reaction for copper with potassic ferrocyanide. Ignite 

 the precipitate and filter separately. The residue con- 

 tains 34.31" |„ of sulphuric anhydride, SO3, or 13.73"!, of 

 sulphur. 



