ANALYSIS.

1. Determination of Free Caustic Alkali.—Put 20 grams of the sample into a 100 cc. flask, dilute with approximately 50 cc. of freshly boiled distilled water, add an excess of neutral barium chloride solution, 1 cc. of phenolphthalein solution, make up to the mark and mix. Allow the precipitate to settle, draw off 50 cc. of the clear liquid and titrate with normal acid (N/1). Calculate the percentage of Na₂O existing as caustic alkali.

2. Determination of Ash and Total Alkalinity.—Weigh 2 to 5 grams of the sample in a platinum dish, burn off the glycerine over a luminous Argand burner or other source of heat,[19] giving a low temperature, to avoid volatilization and the formation of sulphides. When the mass is charred to the point that water will not be colored by soluble organic matter, lixiviate with hot distilled water, filter, wash and ignite the residue in the platinum dish. Return the filtrate and washings to the dish, evaporate the water, and carefully ignite without fusion. Weigh the ash.

Dissolve the ash in distilled water and titrate total alkalinity, using as indicator methyl orange cold or litmus boiling.

3. Determination of Alkali Present as Carbonate.—Take 10 grams of the sample, dilute with 50 cc. distilled water, add sufficient N/1 acid to neutralize the total alkali found at (2), boil under a reflux condenser for 15 to 20 minutes, wash down the condenser tube with distilled water, free from carbon dioxide, and then titrate back with N/1 NaOH, using phenolphthalein as indicator. Calculate the percentage of Na₂O. Deduct the Na₂O found in (1). The difference is the percentage of Na₂O existing as carbonate.

4. Alkali Combined with Organic Acids.—The sum of the percentages of Na₂O found at (1) and (3) deducted from the percentage found at (2) is a measure of the Na₂O or other alkali combined with organic acids.

5. Determination of Acidity.—Take 10 grams of the sample, dilute with 50 cc. distilled water free from carbon dioxide, and titrate with N/1 NaOH and phenolphthalein. Express in terms of Na₂O required to neutralize 100 grams.

6. Determination of Total Residue at 160° C.—For this determination the crude glycerine should be slightly alkaline with Na₂CO₃ not exceeding 0.2 per cent. Na₂O, in order to prevent loss of organic acids. To avoid the formation of polyglycerols this alkalinity must not be exceeded.

Ten grams of the sample are put into a 100 cc. flask, diluted with water and the calculated quantity of N/1 HCl or Na₂CO₃ added to give the required degree of alkalinity. The flask is filled to 100 cc., the contents mixed, and 10 cc. measured into a weighed Petrie or similar dish 2.5 in. in diameter and 0.5 in. deep, which should have a flat bottom. In the case of crude glycerine abnormally high in organic residue a smaller amount should be taken, so that the weight of the organic residue does not materially exceed 30 to 40 milligrams.

The dish is placed on a water bath (the top of the 160° oven acts equally well) until most of the water has evaporated. From this point the evaporation is effected in the oven. Satisfactory results are obtained in an oven [20] measuring 12 ins. cube, having an iron plate 0.75 in. thick lying on the bottom to distribute the heat. Strips of asbestos millboard are placed on a shelf half way up the oven. On these strips the dish containing the glycerine is placed.

If the temperature of the oven has been adjusted to 160° C. with the door closed, a temperature of 130° to 140° can be readily maintained with the door partially open, and the glycerine, or most of it, should be evaporated off at this temperature. When only a slight vapor is seen to come off, the dish is removed and allowed to cool.

An addition of 0.5 to 1.0 cc. of water is made, and by a rotary motion the residue brought wholly or nearly into solution. The dish is then allowed to remain on a water bath or top of the oven until the excess water has evaporated and the residue is in such a condition that on returning to the oven at 160° C. it will not spurt. The time taken up to this point cannot be given definitely, nor is it important. Usually two or three hours are required. From this point, however, the schedule of time must be strictly adhered to. The dish is allowed to remain in the oven, the temperature of which is carefully maintained at 160° C. for one hour, when it is removed, cooled, the residue treated with water, and the water evaporated as before. The residue is then subjected to a second baking of one hour, after which the dish is allowed to cool in a desiccator over sulphuric acid and weighed. The treatment with water, etc., is repeated until a constant loss of 1 to 1.5 mg. per hour is obtained.

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 Na₂CO₃ to NaCl. The corrected weight multiplied by 100 gives the percentage of total residue at 160° 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 160° C. Report as organic residue at 160° C. (it should be noted that alkaline salts of fatty acids are converted to carbonates on ignition and that the CO₃ thus derived is not included in the organic residue).