58 COMPOSITION OF AMEKICAN WINES. 



When the distillation is finished the contents of the U-'tube are washed 

 into the flask and the excess of iodin determined with standardized 

 thiosulphate solution. On account of its lack of permanence, the iodin 

 solution employed should be titrated from time to time with a decinor- 

 mal thiosulphate solution (containing 24.8 grams Na 2 S 2 O 3 .5 H 2 O per 

 liter). The number of cubic centimeters of decinormal iodin solution 

 employed, less the number of cubic centimeters of thiosulphate solu- 

 tion required at the end of the determination, is multiplied by 0.0032 

 for the grams of sulphur dioxid per 100 cc of wine. 



Fairly accurate results may also be obtained by the following 

 method: 



Twenty-five cc of a solution of potassium hydroxid (56 grams per 

 liter) are placed in a flask having a capacity of approximately 200 cc. 

 Fifty cc of the wine are introduced by means of a pipette and mixed 

 with the potassium hydroxid. The mixture is allowed to stand for 

 fifteen minutes, with occasional agitation. Ten cc of 1-3 sulphuric 

 acid are added, also a few cubic centimeters of starch solution; the 

 mixture is then titrated with n / 50 iodin solution. The iodin solu- 

 tion is introduced as rapidly as possible and the addition continued 

 until the blue color will last for several minutes. The number of 

 cubic centimeters of the iodin solution employed, multiplied by 0.00128, 

 gives the weight of the total sulphurous acid expressed in grams per 

 100 cc. 



ESTIMATION OP FREE SULPHUROUS ACID. 



Fifty cc of the wine are treated, in a flask having a capacity of 

 approximately 200 cc, with 5 cc of 1-3 sulphuric acid, a small piece of 

 sodium carbonate added to expel the air, and the sulphurous acid 

 titrated with n / 50 iodin solution as directed under total sulphurous acid. 



The number of cubic centimeters of iodin solution employed, multi- 

 plied by 0.00128, gives the weight of the free sulphurous acid expressed 

 in grams per 100 cc. 



DETECTION OF PRESERVATIVES. 



The preservatives commonly tested for in wines are salicylic acid, 

 benzoic acid, saccharin, abrastol, hydronaphthol, boric acid, boro- 

 fluorides, and silicofluorides. Of these the salicylic and benzoic acids 

 are both somewhat commonly employed. Abrastol is said to be used 

 to some extent in Europe, but has not yet been reported in Ameri- 

 can wines. Hydronaphthol has been used in rare instances, and is 

 still used with sufficient frequency to warrant more consideration 

 than it usually receives from food laboratories. Boric acid is better 

 known as a preservative for milk and meat preparations than for 

 fruits and fruit preparations. It is sometimes used, however, in both 

 wine and beer. Its detection is a somewhat more delicate matter 



