SOAP. 67 



One cubic centimeter of tenth-normal stearic acid = 0.004 gram of caustic 

 soda or 0.0053 gram of sodium carbonate. These liguros calculated to percent- 

 age would be: 0.86 per cent of caustic soda and 1.99 per cent of sodium car- 

 bonate. 



It is to be noted that a rubber stopper can not be used in the flasks used 

 for dissolving the soap on account of the sulphur in the rubber which decolor- 

 izes an alcoholic solution of phenolphthalein. The method is applicable to all 

 soaps that do not contain fillers which react with the standard solutions 

 employed. 



7. Unsaponified Matter. 



Dissolve 5 grams of soap in 50 cc of 50 per cent alcohol ; if any free fatty 

 acids are present add just enough standard alkali to neutralize them and wash 

 into a separatory funnel with 50 per cent alcohol. Extract with 100 cc of gaso- 

 line (B. P. 50- 60). Wash the gasoline with water, evaporate, and weigh as 

 unsaponified. This may consists of fat that has not been converted into soap or 

 of hydrocarbon oils. 



8. Rosin. 



If much unsaponified matter is present, prepare dry fatty and rosin acids 

 from the portion from which the unsaponified matter has been removed. Dis- 

 solve 3 grams of the dry mixed acids in 25 cc of absolute alcohol in a 100 cc 

 stoppered flask, place the flask in cold water and shake; add 25 cc of absolute 

 alcohol saturated with dry hydrochloric acid, shake occasionally, and let the 

 action go on for twenty minutes ; then add 10 grams of dry granular zinc chlorid, 

 shake, and allow to stand for twenty minutes. Pour the contents of the flask into 

 200 cc of water in a 500 cc beaker, and rinse out the flask with dilute alcohol. 

 Put a small stick of metallic zinc in the beaker and boil off the alcohol. Cool, 

 transfer to a separatory funnel, extract with gasoline, wash the gasoline until 

 free from hydrochloric acid, distil off the gasoline, dissolve in neutral alcohol, 

 and titrate with standard alkali using phenolphthalein as indicator. (One cubic 

 centimeter of normal alkali corresponds to 0.346 gram of rosin.) The rosin 

 may be determined gravimetrically by washing the gasoline extract with water. 

 It is not necessary to wash absolutely free from acid. Then treat the extract 

 in the funnel with a solution of 5 grams of potassium hydroxid and 5 cc of 

 alcohol in 50 cc of water. Upon shaking, the rosin is rapidly saponified and 

 the two layers separate well. Draw off the rosin soap, wash the gasoline once 

 with water, add the washings to the soap solution, add an excess of acid, extract 

 the rosin with gasoline, evaporate the gasoline, and weigh the rosin. 



9. Silica and Silicates. 



Insoluble silicates, sand, etc., are present in the insoluble; but sodium silicate 

 fillers will only show by forming pasty liquids. When sodium silicate is sus- 

 pected, ash the soap (10 grams), add an excess of hydrochloric acid to the ash, 

 evaporate to dryness; add hydrochloric acid and again evaporate to dryness; 

 cool, moisten with hydrochloric acid, dissolve in water, filter, wash, evaporate 

 the filtrate to dryness, and again take up with hydrochloric acid and water, 

 filter, and wash. Unite the precipitates, ignite, and weigh as silicon dioxid; 

 calculate to sodium silicate (Xa-Si^o). If metals other than the alkalis are 

 suspected, the filtrate from the silica determination may be examined. 



