342 FOOD AND FOOD ADULTERANTS. 



Very white wines, if entirely free from carbonic acid, may be titrated 

 with phenol-phthaliue as an indicator. From 10 to 25cc. of wine may 

 conveniently be taken for titration. It is very desirable to estimate 

 both the fixed and volatile free acids in wine, and to this end the latter 

 should be determined directly ; all methods for this estimation by differ- 

 ence by evaporating the wine to dryuess, and titrating the residue, hav- 

 ing been shown to be faulty. The German method is to distill off the 

 acetic and other volatile acids in a current of steam ; and I have found it 

 a most satisfactory one, giving very coincident results when carefully 

 carried out, the only objection being that it is a little tedious. The 

 theory of the method is that acetic acid, which forms the greater part of 

 the pure volatile acids, while it does not distill off at a temperature 

 lower than 120 C., can still be distilled off at a lower temperature than 

 its boiling point by passing through the liquid in which it is contained 

 a current of steam, providing that the quantity of water passed through 

 in the shape of steam is about four times as great as the quantity of the 

 liquid in which the acid is contained. The manner of applying it is as 

 follows : 



Fifty cc. of the wine are measured into a flask of about 300cc. ca- 

 pacity, which is connected with a condenser by one tube which passes 

 just below the rubber stopper, which is also perforated by another tube 

 which reaches to the bottom of the flask and terminates there in a finely 

 drawn out point ; this tube is bent at right angles where it passes out of 

 the flask, and connects it with a larger flask placed alongside which con- 

 tains about 300cc. of water, being also provided with a safety tube. 

 When the operation is begun, lamps are placed under the two flasks 

 and the contents of both brought to a boil, when the flame under the 

 flask containing the wine is lowered somewhat and the distillation so 

 conducted that after 200cc. have distilled off the wine shall not be de- 

 creased to less than one-third or one-fourth of its original volume. The 

 200cc. of distillate is received in a properly graduated flask, and titrated 

 with standard alkali, using pheuol-phthaline as an indicator. 



The number of cubic centimeters of normal alkali required for the 

 titration of the volatile acids, subtracted from the number of cubic 

 centimeters required for the neutralization of 50cc. of the original wine, 

 gives the amount of alkali neutralized by the freejixcd acids; the total 

 free acids and free fixed adds are generally calculated as tartaric, the 

 volatile as acetic acid. 1 



BITARTRATE OF POTASH. 



The German Commission gives two methods, as follows : 



ID two stoppered flasks two samples of 20cc. of Avine each are treated with '200cc. 

 ether-alcohol (equal volumes), after adding to oue flask 2-:> drops of a 'JO percent. 

 solution of acetate of potash. The mixtures are well .shaken and allowed to stand 

 16 to 18 honn at a low temperature (0-10C.), the precipitate tiitereti <>iv, \\aslu d \\-ith 



1 One cubic centimeter of normal alkali neutralizes .075 graui of tartaric, .00 gram 

 of acetic acid. 



