236 VINEGAR, CIDER, AND FRUIT-WINES. 



some litmus tincture, added ; the whole is then heated until the 

 precipitate is dissolved and effervescence has ceased, but the solu- 

 tion retains a slight red coloration. Now add drop by drop nor- 

 mal sodium until the color turns blue. If, for instance, 3 cubic 

 centimetres of normal sodium have been used, 20 3 = 17 cubic 

 centimeters of normal nitric acid have been required for the solu- 

 tion of the barium carbonate. Since 1 equivalent of barium car- 

 bonate saturates 1 liter of normal nitric acid, or 98.5 grammes 

 of the former 1000 cubic centimetres of the latter, each cubic cen- 

 timetre of normal nitric acid consumed indicates 0.0985 gramme 

 of barium carbonate ; hence in our example 1.674 gramme of car- 

 bonate has not been dissolved by the acid ; there was therefore 

 dissolved 3 1.674 = 1.326 gramme. And finally, as, according 

 to the above, each gramme of barium carbonate indicates 6.09 

 per cent, of acetic anhydride, this wood-vinegar contains 1.326. 

 6.09 =* 8 per cent. 



L. Kieffer's method is based upon the following : Dissolve 

 sulphate of copper in water, and after taking a small portion 

 (about 3-l-g-) of it away, gradually add to the remainder ammonia 

 until the pale green precipitate at first formed is redissolved ; 

 then add the retained portion of the solution, and, after shaking 

 and corking the flask, allow it to stand for a few hours. The 

 dark blue fluid is only fit for use when the ammonia is thoroughly 

 saturated with oxide of copper, i. e., when some of the precipitate 

 remains undissolved. The solution is now filtered and standard- 

 ized to normal nitric acid. 



By gradually adding this solution to an acid, for instance nor- 

 mal nitric acid, the oxide of copper as well as the ammonia is 

 fixed by the acid and two soluble salts are formed, in this case 

 nitrate of copper and of ammonia. If finally the acid is saturated 

 and a drop of the blue solution be added, a pale blue precipitate 

 is formed, because the ammonia contained in the drop combines 

 with an equivalent quantity of nitric acid in the nitrate of copper 

 so that not only the oxide of copper dissolved in the drop is pre- 

 cipitated (as hydrate), but also the quantity combined with the 

 nitric acid. 



Thus take, for instance, 5 cubic centimetres of normal nitric 

 acid and add the blue solution drop by drop with shaking from a 



