X] FOOD PRESERVATIVES 151 



phoric acid solution, until 150 cc. have passed over. Collect the distillate in about 

 100 cc. of nearly saturated bromin water, allowing the end of the condenser to dip 

 below the surface. The method and apparatus may be simplified without material 

 loss in accuracy by omitting the current of carbon dioxid, adding 10 cc. of phosphoric 

 acid instead of 5 cc, and dropping into the distillation flask, immediately before 

 attaching the condenser, a piece of sodium bicarbonate weighing not more than 

 1 gram. The carbon dioxid liberated is not sufficient to expel the air entirely from 

 the apparatus, but will prevent oxidation to a large extent. When the distillation 

 is finished, boil off the excess of bromin, dilute the solution to about 250 cc, add 5 

 cc. of hydrochloric acid (1 to 3), heat to boiling, and precipitate the sulphuric acid 

 with 10% barium chlorid solution. Boil for a few minutes longer, allow to stand 

 overnight in a warm place, filter on a weighed Gooch, wash with hot water, ignite 

 at a dull red heat, and weigh as barium sulphate. 



31 Method II.— Direct Titration Method. 



In the examination of wine, fairly accurate results may be obtained by the fol- 

 lowing method : 



Place 25 cc. of 5.6% potassium hydroxid solution in a 200 cc. flask. Introduce 

 50 cc. of the sample, mix with the potassium hydroxid solution, and allow the mix- 

 ture to stand for 15 minutes with occasional agitation. Add 10 cc. of sulphuric acid 

 (1 to 3) and a few cc. of starch solution, and titrate the mixture with N/50 iodin solu- 

 tion. Introduce the iodin solution as rapidly as possible and continue the addition 

 until the blue color persists for several minutes. One cc. of N/50 iodin is equiva- 

 lent to 0.00064 gram of sulphur dioxid. 



DETERMINATION OF FREE SULPHUROUS ACID, 



32 (Especially Adapted to Wine.) 



Treat 50 cc. of the sample in a 200 cc. flask with about 5 cc. of sulphuric acid 

 (1 to 3) add about 0.5 gram of sodium carbonate to expel the air, and titrate the sul- 

 phurous acid with N/50 iodin, as directed under 31. 



BETA-NAPHTHOL. 



33 Qualitative Test. 



Extract 200 cc. of the sample, or of its aqueous extract, prepared as directed 

 under 1 (C), with 10 cc of chloroform in a separatory funnel. To the chloroform 

 extract in a test tube add a few drops of alcoholic potash, and place in a boiling 

 water bath for 2 minutes. The presence of beta-napthol is indicated by the forma- 

 tion of a deep blue color, which changes to green and then to yellow. 



ABRASTOL. 



QUALITATIVE TESTS. 



34 Sinibaldi Method.^* 



Make 50 cc. of the sample alkaline with a few drops of ammonium hydroxid and 

 extract with 10 cc. of amyl alcohol, adding ethyl alcohol if an emulsion is formed. 

 Decant the amyl alcohol, filter if turbid, and evaporate to dryness. Add to the 

 residue 2 cc. of nitric acid (1 to 1), heat on the water bath until half of the liquid 

 is evaporated, and transfer to a test tube with the addition of 1 cc. of water. Add 

 about 0.2 gram of ferrous sulphate and an excess of ammonium hydroxid, drop by 



