In the case of acid glycerine a correction must be made for the alkali added 1 cc. _N_/1 alkali represents an addition of 0.03 gram. In the case of alkaline crudes a correction should be made for the acid added. Deduct the increase in weight due to the conversion of the NaOH and Na_{2}CO_{3} to NaCl. The corrected weight multiplied by 100 gives the percentage of _total residue at 160deg. C._ This residue is taken for the determination of the non-volatile acetylizable impurities (see acetin method). 7. _Organic residue._--Subtract the ash from the total residue at 160deg. C. Report as organic residue at 160deg. C. (it should be noted that alkaline salts of fatty acids are converted to carbonates on ignition and that the CO_{3} thus derived is not included in the organic residue). ACETIN PROCESS FOR THE DETERMINATION OF GLYCEROL. This process is the one agreed upon at a conference of delegates from the British, French, German and American committees, and has been confirmed by each of the above committees as giving results nearer to the truth than the bichromate method on crudes in general. It is the process to be used (if applicable) whenever only one method is employed. On pure glycerines the results are identical with those obtained by the bichromate process. For the application of this method the crude glycerine should not contain over 60 per cent. water. REAGENTS REQUIRED. (_A_) _Best Acetic Anhydride._--This should be carefully selected. A good sample must not require more than 0.1 cc. normal NaOH for saponification of the impurities when a blank is run on 7.5 cc. Only a slight color should develop during digestion of the blank. The anhydride may be tested for strength by the following method: Into a weighed stoppered vessel, containing 10 to 20 cc. of water, run about 2 cc. of the anhydride, replace the stopper and weigh. Let stand with occasional shaking, for several hours, to permit the hydrolysis of all the anhydride; then dilute to about 200 cc., add phenolphthalein and titrate with _N_/1 NaOH. This gives the total acidity due to free acetic acid and acid formed from the anhydride. It is worthy of note that in the presence of much free anhydride a compound is formed with phenolphthalein, soluble in alkali and acetic acid, but insoluble in neutral solutions. If a turbidity is noticed toward the end of the neutralization it is an indication that the anhydride is incompletely hydrolyzed and inasmuch as the indicator is withdrawn from the solution, results may be incorrect.