288 VINEGAR, CIDER, AND FRUIT-WINES. 



moment turbidity ceases. This test is better than with litmus, 

 considerable experience being required to hit the right point with 

 the latter on account of solution of sugar of lead showing a slight, 

 but perceptible, acid reaction. 



The solution of litharge in acetic acid is promoted by heat and 

 is effected either in a copper pan, the bottom and sides of which 

 are brought in contact with a few bright sheets of lead (to pre- 

 vent the copper from being attacked), or in a lead pan over an 

 open fire, or in a wooden vat into which steam is introduced. 

 The clear solution is evaporated. If this is to be done over an 

 open fire, it is recommended to have a preparatory heating pan for 

 each evaporating pan, as described in the preparation of calcium 

 acetate, the preparatory heating pan, which is heated by the es- 

 caping gases, being used for the solution of the litharge in acetic 

 acid. Lead pans, if used, should rest upon strong cast-iron plates. 

 The dimensions of the pans vary very much ; according to 

 Assmus, they are 6J feet long, 4 feet wide, and from 12 to 14 inches 

 deep, while the depth of the preparatory heating pans is from 24 

 to 28 inches. From the latter, which stand at a higher level, 

 the clear solution is discharged, through a stop-cock just above 

 the bottom, into the evaporating pans. Evaporation should be 

 effected at a moderate heat ; actual boiling must be strictly 

 avoided, as otherwise large losses of acetic acid are unavoidable 

 and the solution readily acquires a yellow coloration. 



According to the degree of evaporation (to 36 B. or to 46 B. 

 or more) of the sugar of lead solution, distinct crystals are ob- 

 tained or only a radiated crystalline mass. With a perfectly 

 pure solution, the first method is the best, since crystals bring a 

 better price. The mother-lye, after being again acidulated, is 

 once more evaporated and acidulated, and yields more crystals. 



Stein recommends the conducting of the vapors of acetic acid or 

 of vinegar into litharge mixed with a very small quantity of water. 

 This method is in general use in Germany. But as the extract 

 remaining in the still retains a considerable quantity of acetic 

 acid, especially if beer had been added to the liquid used in the 

 preparation of the vinegar, it is advisable to increase the boiling 

 point of the latter by the addition of one-third of its weight of 

 common or rock salt. At first the water condenses in the receiver 



