xxin] 



FATS AND OILS 



309 



tions of neutral 90% alcohol by volume through the filter, each portion previously- 

 passed through the condenser, the 25 cc. cylinder and the 110 cc. receiving flask. 

 Titrate the combined alcoholic washings with N/10 sodium hydroxid, using phenol- 

 phthalein as an indicator. 



Run a blank in the same manner and subtract the quantity of the standard alkali 

 required to neutralize the 45 cc. of alcohol, used in washing the apparatus and filter 

 paper of the blank, from that required in each Polenske determination. Report 

 the Polenske number as the number of cc. of N/10 alkali required to neutralize the 

 insoluble volatile acids from the 110 cc. of distillate as obtained above. Since the 

 entire distillate is filtered it is not necessaiy to multiply the burette reading by 1.1, 

 as in 25, but a calculation must be made, as directed in 25, to reduce the actual 

 number of cc. found in the titration to the number which would have been required 

 had exactly 5 grams of fat been used. 



FIG. 13. APPARATUS' FOR THE DETERMINATION OF THE POLENSKE NUMBER. 



29 



LIQUID AND SOLID FATTY ACIDS. 

 Muter Method, Modified hy Lane^. — Tentative. 



Weigh 5 grams of the oil or fat into an Erlenmeyer flask, saponify, precipitate with 

 lead acetate solution and treat the precipitated lead soap with ether, as directed 

 under 37. Filter the ether solution of the soluble lead soap into a Muter tube or 

 separatory funnel and decompose the soap by shaking with 40 cc. of hydrochloric 

 acid (1 to 5). The soap is completely decomposed when the ether becomes clear 

 and colorless. 



Draw off the lead chlorid from the ether solution and wash the ether free from 

 acid. Evaporate, until free from ether, an aliquot of this solution in an atmosphere 

 of carbon dioxid, in order t!o prevent the oxidation of the oleic acid, and weigh to 

 determine the per cent of liquid acids; determine the iodin number as directed in 

 16 or 18, using 0.2-0.3 gram of this residue. 



