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5.10 SOLIDIFICATION TEMPERATURE OF FATTY ACIDS

5.10 SOLIDIFICATION TEMPERATURE OF FATTY ACIDS

Preparation of the Fatty Acids

 ​           Heat 75 ml of glycerol-potassium hydroxide solution (made by dissolving 25 g of potassium hydroxide in 100 ml of glycerol) in an 800-ml beaker to 150º, and add 50 ml of the clarified fat, melted if necessary. Heat the mixture for 15 minutes with frequent stirring, but do not allow the temperature to rise above 150º. Saponification is complete when the mixture is homogeneous, with no particles clinging to the beaker at the meniscus. Pour the contents of the beaker into 500 ml of nearly boiling water in an 800-ml beaker or casserole, add slowly 50 ml of diluted sulfuric acid (1 in 4), and heat the solution, with frequent stirring, until the fatty acids separate cleanly as a transparent layer. Wash the acids with boiling water until free from sulfuric acid, collect them in a small beaker, place on a water-bath until the water has settled and the fatty acids are clear, filter into a dry beaker while hot, and dry at 105º for 20 minutes. Place the warm fatty acids in a suitable container, and cool in an ice bath until they congeal.

Test for Complete Saponification

 ​           Place 3 ml of the dry acids in a test-tube, and add 15 ml of ethanol. Heat the solution to boiling, and add an equal volume of ammonia TS. A clear solution results.

Procedure

 ​           Using an apparatus similar to the “Freezing Temperature Apparatus” specified therein, proceed as directed for Procedure under “Determination of Freezing Temperature” (Appendix 4.4), reading “solidification temperature” for “freezing or congealing temperature” (the terms are synonymous). The average of not less than four consecutive readings of the highest point to which the temperature rises is the solidification temperature of the fatty acids.

APPENDICES • 5.10 SOLIDIFICATION TEMPERATURE OF FATTY ACIDS
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หมายเหตุ / Note : TP II 2011 PAGE 483