FRUITS AND FKUIT PRODUCTS. 79 



tenths of a degree either to the right or to the left. a If a Schmidt and Hacnscli 

 polariscope be used and a 10 per cent solution be polari/ed in a 200-mm tube, the 

 number of degrees read on the sugar scale of the instrument multiplied by 0.8755 

 will give the percentage of dextrin, or the following formula 1 ' may be used: 



0X1,000 XV 

 Percentage of dextrin = 19g ^ L x ~^ 



in which 



C=degrees of circular rotation, 



V=volume in cubic centimeters of solution polarized, 



L= length of tube in centimeters, 



W= weight of sample in solution in grams. 



16. DETERMINATION OF ALCOHOL PRECIPITATE. 



Take 100 cc of a 20 per cent solution of jelly [see 2 (a)], diluted sirup, or of the 

 washings from the determination of insoluble solids, and evaporate to 20 cc; then add 

 slowly and with constant stirring 200 cc of 95 to 96 per cent alcohol and allow the 

 mixture to stand overnight. Filter and wash with 80 per cent alcohol by volume. 

 Wash this precipitate off the filter paper with hot water into a platinum dish; evap- 

 orate to dry ness; dry at 100 C. for several hours and weigh; then burn off the organic 

 matter and weigh the residue as ash. The loss in weight upon ignition is called alcohol 

 precipitate. 



The ash should be largely lime and not more than 5 per cent of the total weight of 

 the alcohol precipitate. If it is larger than this some of the salts of the organic 

 acids have been brought down. Titrate the water-soluble portion of this ash with 

 decinormal acid, as any potassium bitartrate precipitated by the alcohol can" thus be 

 estimated. 



The general appearance of the alcohol precipitate is one of the best indications as to 

 the presence of glucose and dextrin. Upon the addition of alcohol to a pure fruit 

 product a flocculent precipitate is formed with no turbidity, while in the presence of 

 glucose a white turbidity appears at once upon adding the alcohol, and a thick, gummy 

 precipitate forms. 



17. DETERMINATION OF TARTARIC, CITRIC, AND MALIC ACIDS. c 



Use the filtrate from the alcohol precipitate in the determination of the organic 

 acids. After evaporating off the alcohol and taking up the acids with water add 

 lead subacetate until the solution is alkaline, then filter and wash the precipitate 

 until only a slight amount of lead remains in the washings. Wash the precipitate 

 off the filter paper into a beaker with hot water, precipitate the lead by hydrogen 

 sulphid and filter off the lead sulphid while hot, washing with hot \vater. Evaporate 

 the filtrate which contains the free organic acids to about 50 cc, neutralize exactly 

 with potassium hydroxid, add an excess of strong solution of neutral calcium acetate 

 with constant stirring, and allow to stand from 6 to 12 hours. Throw the precipitate 

 of calcium tartrate on a filter paper and -wash until filtrate and washings make 

 exactly 100 cc; ignite the filter paper and precipitate, and determine the lime and 

 tartaric acid by titration. A correction of 0.0286 grams of tartaric acid, which is 

 held in solution in the 100 cc of washings as calcium tartrate, must be added. 

 Now evaporate the filtrate down to about 20 cc, and. if a precipitate of calcium citrate 

 is formed tilter it off hot, wash with hot water, ignite, and titrate the lime. From 



r. s. I )(-]>. of AKI-., Div. of Chem., Bui. 66. 

 Wiley, Chem. News, issii, 4(>, 17. r >. 



cAiiMHlilirntion of Schmidt ^ Hu-pr's method. U.S. Dept. of Agr., Div.of Chem., Bui. 4 revised. 

 p. 67; Ztschr. anal. Chem., 1882, 21, 634-641. 



