SOAP. 65 



3. Insoluble Matter. 



Dissolve 5 grams of soap in hot water (use about 75 cc). Filter on a 

 gooch or weighed paper and wash with hot water; dry at 105 C., weigh, and 

 calculate the percentage of total insoluble. Ignite the residue and calculate the 

 percentage of insoluble mineral matter. 



4. Total Fatty Matter. 



To the filtrate from the insoluble matter add 40 cc of half-normal sulphuric 

 acid, heat on the water bath until the fatty acids have collected in a clear layer 

 on top, cool in ice water, remove the layer of fatty acids, and wash with water ; 

 then heat again with water, cool, remove fatty layer, wash with ice water, dry 

 with filter paper, unite the acid liquids, transfer to a separatory funnel, and 

 shake out with two portions of 50 cc each of gasoline ; wash the gasoline twice 

 with 20 cc of water. Evaporate off the gasoline, add the cake of fatty acids, 

 etc., dry at 100, and weigh as total fatty matter. This may represent fatty 

 acids, uncombined fat, rosin and hydrocarbons. 



5. Total Alkali. 



Heat the acid liquid obtained from the determination of total fatty matter 

 to drive off traces of gasoline, cool, add methyl orange, and titrate the excess of 

 acid with fifth-normal alkali. From this titration calculate the amount of acid 

 neutralized by alkali in soap and figure to percentage of sodium monoxid. 



A more rapid method is to ash the soap, dissolve the ash in water, and titrate. 

 This method gives good results in the absence of silica or other mineral fillers, 

 but can not be used in their presence. 



6. Free Alkali, 

 (a) ALCOHOLIC METHOD. 



Treat the freshly cut surface of the soap with a few drops of an alcoholic 

 solution of phenolphthalein ; if it does not turn red it may be assumed that free 

 caustic alkali is absent. If free alkali is present, dissolve 2 grams of the soap 

 in 100 cc of neutral alcohol (heat is necessary to complete the solution), filter 

 frpm the undissolved sodium carbonate, etc.; wash with alcohol, add phenol- 

 phthalein, titrate with standard acid, and calculate to per cent of free alkali as 

 sodium hydroxid. Should the alcoholic solution be acid instead of alkaline, 

 titrate with standard alkali and calculate the percentage of free fatty acid as 

 oleic acid. 



Wash the portion insoluble in alcohol with water, add methyl orange to the 

 washings, and titrate with half-normal sulphuric acid. Calculate to percentage 

 of sodium monoxid present as carbonate, or possibly as borate or silicate. If 

 borax is present boil off the carbon dioxid after neutralizing exactly to methyl 

 orange ; cool, add mannite and phenolphthalein, and titrate the boric acid with 

 standard alkali. 



(b) DEVINE'S METHOD. 



The alcohol method of determining free alkali is open to the objection that 

 if the soap contains free alkali and free fat also, by the heating with alcohol 

 the fat will be partly or completely saponified and the free alkali may not be 



