XVI] WINES 241 



(C) Indigo solution. — Dissolve 6 grams of sodium sulphindigotate in 500 cc. of 

 water by heating; cool, add 50 cc. of concentrated sulphuric acid, make up to 1 

 liter and filter. 



(d) Purified honehlac¥\—Bo\\ 100 grams of finely powdered boneblack with suc- 

 cessive portions of hydrochloric acid (1 to 3), filter and wash with boiling water until 

 free from chlorin. Keep covered with water. 



32 DETERMINATION^. 



Dealcoholize 100 cc. of the wine by evaporation and dilute with water to the 

 original volume. Transfer 10 cc. to a 2 liter porcelain dish; add about a liter of 

 water and exactly 20 cc. of the indigo solution. Add the standard potassium 

 permanganate solution, 1 cc. at a time, until the blue color changes to green; then add 

 a few drops at a time until the color becomes golden yellow. Designate the number 

 of cc. of permanganate solution used as "a". 



Treat 10 cc. of the dealcoholized wine, prepared as above, with boneblack for 

 15 minutes; filter and wash the boneblack thoroughly with water. Add a liter of 

 water and 20 cc. of the indigo solution and titrate with permanganate as above. 

 Designate the number of cc. of permanganate used as "b". 



Then a— b = c, the number of cc. of the permanganate solution required for the 

 oxidation of the tannin and coloring matter in 10 cc. of the wine. 



33 CRUDE PROTEIN.-TENTATIVE. 



Determine nitrogen in 50 cc. of the wine, as directed under I, 18, 21 or 23, and 

 multiply the result by 6.25. 



34 PENTOSANS.-TENTATIVE. 



Proceed as directed in VIII, 64, except that 100 cc. of the wine and 43 cc. of hy- 

 drochloric acid (sp. gr. 1.19) are used in beginning the distillation. Owing to the 

 interference of sugars this determination can be made in dry wines only. 



35 GUM AND DEXTRIN.— TENTATIVE. 



Evaporate 100 cc. of the wine to about 10 cc. and add 10 cc. of 96% alcohol by 

 volume. If gum or dextrin be present (indicated by the formation of a voluminous 

 precipitate), continue the addition of alcohol, slowly and with stirring, until 100 

 cc. have been added. Let stand overnight, filter, and wash with 80% alcohol by 

 volume. Dissolve the precipitate on the paper with hot water, hydrolyze the 

 filtrate and washings with hydrochloric acid and proceed as directed under VIII, 60. 



36 NITRATES.— TENTATIVE. 



(a) White vxine. — Treat a few drops of the wine in a porcelain dish with 2-3 cc. 

 of concentrated sulphuric acid, which contains about 0.1 gram of diphenylamin* 

 per 100 cc. The deep blue color formed in the presence of nitrates appears so quickly 

 that it is not obscured, even in sweet wine, by the blackening produced by the ac- 

 tion of sulphuric acid on the sugar. 



(b) Red vxine. — Clarify with basic lead acetate, filter, remove the excess of lead 

 from the filtrate with sodium sulphate, filter again and treat a few drops of this 

 filtrate as directed under (a). 



37 COLORING MATTERS.-TENTATIVE. 

 Proceed as directed under XI. 



