BICHROMATE PROCESS FOR GLYCEROL DETERMINATION. REAGENTS REQUIRED.
(A) Pure potassium bichromate powdered and dried in air free from dust or organic vapors, at 110° to 120° C. This is taken as the standard.
(B) Dilute Bichromate Solution.—7.4564 grams of the above bichromate are dissolved in distilled water and the solution made up to one liter at 15.5° C.
(C) Ferrous Ammonium Sulphate.—It is never safe to assume this salt to be constant in composition and it must be standardized against the bichromate as follows: dissolve 3.7282 grams of bichromate (A) in 50 cc. of water. Add 50 cc. of 50 per cent. sulphuric acid (by volume), and to the cold undiluted solution add from a weighing bottle a moderate excess of the ferrous ammonium sulphate, and titrate back with the dilute bichromate (B). Calculate the value of the ferrous salt in terms of bichromate.
(D) Silver Carbonate.—This is prepared as required for each test from 140 cc. of 0.5 per cent. silver sulphate solution by precipitation, with about 4.9 cc. N/1 sodium carbonate solution (a little less than the calculated quantity of N/1 sodium carbonate should be used as an excess to prevent rapid settling). Settle, decant and wash one by decantation.
(E) Subacetate of Lead.—Boil a 10 per cent. solution of pure lead acetate with an excess of litharge for one hour, keeping the volume constant, and filter while hot. Disregard any precipitate which subsequently forms. Preserve out of contact with carbon dioxide.
(F) Potassium Ferricyanide.—A very dilute, freshly prepared solution containing about 0.1 per cent.