Packaging and storage—
Preserve in tight, light-resistant containers, and prevent exposure to excessive heat.
Identification—
Saponify 5 g by boiling with 2.5 mL of 7.5 N sodium hydroxide and 12.5 mL of alcohol. Evaporate the alcohol, dissolve the soap in 50 mL of hot water, and add hydrochloric acid until the free fatty acids separate as an oily layer. Cool the mixture, and remove the separated fatty acids and dissolve them in 75 mL of ether. To the ether solution add a hot solution of 4 g of lead acetate in 40 mL of alcohol, and allow the mixture to stand for 18 hours. Filter the supernatant, and transfer the precipitate to the filter with the aid of ether. Place the precipitate in a mixture of 40 mL of 3 N hydrochloric acid and 20 mL of water, and heat until the oily layer is entirely clear. Cool, decant the water solution, and boil the fatty acids with water that has been acidified with hydrochloric acid, until free from lead. (The fatty acids are free from lead when 100 mg, dissolved in 10 mL of alcohol, is not darkened by the addition of 2 drops of
sodium sulfide TS.) Allow the fatty acids to solidify, and press them dry between filter papers on a cold surface. Dissolve the solid fatty acids in 25 mL of 90 percent alcohol, by heating gently, then cool to 15
and maintain at that temperature until the fatty acids have crystallized. Filter the separated fatty acids, recrystallize them from hot 90 percent alcohol, and dry in a vacuum desiccator for 4 hours: the arachidic acid so obtained melts between 73
and 76
.
Cottonseed oil—
Mix 5 mL in a test tube with 5 mL of a mixture of equal volumes of amyl alcohol and a 1 in 100 solution of sulfur in carbon disulfide, warm the mixture carefully until the carbon disulfide is expelled, and immerse the test tube to one-third of its length in a boiling, saturated solution of sodium chloride: no reddish color develops within 15 minutes.
Rancidity—
Shake 1 mL of a 1 in 10 solution of Peanut Oil in ether with 1 mL of hydrochloric acid, and add 1 mL of a 1 in 1000 solution of phloroglucinol in ether: no red or pink color develops.
Free fatty acids 
401
—
The free fatty acids in 10 g require for neutralization not more than 2.0 mL of 0.020 N sodium hydroxide.
