_Blank Test._--As the acetic anhydride and sodium acetate may contain impurities which affect the result, it is necessary to make a blank test, using the same quantities of acetic anhydride, sodium acetate and water as in the analysis. It is not necessary to filter the solution of the melt in this case, but sufficient time must be allowed for the hydrolysis of the anhydride before proceeding with the neutralization. After neutralization it is not necessary to add more than 10 cc. of the _N_/1 alkali (_D_), as this represents the excess usually present after the saponification of the average soap lye crude. In determining the acid equivalent of the _N_/1 NaOH, however, the entire amount taken in the analysis, 50 cc., should be titrated after dilution with 300 cc. water free from carbon dioxide and without boiling. _Determination of the Glycerol Value of the Acetylizable Impurities._--The total residue at 160deg. C. is dissolved in 1 or 2 cc. of water, washed into the acetylizing flask and evaporated to dryness. Then add anhydrous sodium acetate and acetic anhydride in the usual amounts and proceed as described in the regular analysis. After correcting for the blank, calculate the result to glycerol. WAYS OF CALCULATING ACTUAL GLYCEROL CONTENT. (1) Determine the apparent percentage of glycerol in the sample by the acetin process as described. The result will include acetylizable impurities if any are present. (2) Determine the total residue at 160deg. C. (3) Determine the acetin value of the residue at (2) in terms of glycerol. (4) Deduct the result found at (3) from the percentage obtained at (1) and report this corrected figure as glycerol. If volatile acetylizable impurities are present these are included in this figure. Trimethyleneglycol is more volatile than glycerine and can therefore be concentrated by fractional distillation. An approximation to the quantity can be obtained from the spread between the acetin and bichromate results on such distillates. The spread multiplied by 1.736 will give the glycol. BICHROMATE PROCESS FOR GLYCEROL DETERMINATION. REAGENTS REQUIRED. (_A_) _Pure potassium bichromate_ powdered and dried in air free from dust or organic vapors, at 110deg. to 120deg. 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 15.5deg. 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.