Soap-Making Manual / A Practical Handbook on the Raw Materials, Their Manipulation, Analysis and Control in the Modern Soap Plant.

by Edgar George Thomssen

SAMPLING.

The most satisfactory method available for sampling crude glycerine liable to contain suspended matter, or which is liable to deposit salt on settling, is to have the glycerine sampled by a mutually approved sampler as soon as possible after it is filled into drums, but in any case before any separation of salt has taken place. In such cases he shall sample with a sectional sampler (see appendix) then seal the drums, brand them with a number for identification, and keep a record of the brand number. The presence of any visible salt or other suspended matter is to be noted by the sampler, and a report of the same made in his certificate, together with the temperature of the glycerine. Each drum must be sampled. Glycerine which has deposited salt or other solid matter cannot be accurately sampled from the drums, but an approximate sample can be obtained by means of the sectional sampler, which will allow a complete vertical section of the glycerine to be taken including any deposit.

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.