111(11).] rrULIC DOCUMENT — No. 31. 129 



Supplementary Notes. — As this nictliud is only an arlntraiy 

 one it is essential to adhere strictly to the conditions of operation 

 as laid down if coni])ara(ive results are to be obtained, and by 

 so doing over DO ])er cent, of the soluble acids in butter can be 

 secured in the distillate. llei)eated distillation yields higher 

 results, but is accouii)anied by decomposition of non-volatile 

 acids. 



]]utyric, caprivic, caprylic and capric are the only fatty acids 

 that can be distilled under ordinary pressure without deconi{)o- 

 sition. Laurie is almost insoluble in water but is volatile in a 

 current of steam. 



Most of the natural fats and oils contain but a small amount 

 of volatile (soluble) fatty acids, generally below 1 Reichert- 

 Meissl number. Among the prominent exceptions are butter 

 fat and i)or2)oise, dolphin, croton, cocoanut and palm nut oils. 



(a) Mean Moleeular Weight. 

 The titrated volatile acids ^ resulting from the determination 

 of the Keichert-Meissel number are evaporated in a tared j)lati- 

 num dish and dried to constant weight in an air bath at 100° C. 

 From the weight of the salts and of the alkali present in them 

 the mean molecidar weight (m) can be readily calculated by the 

 following formula : — 



_ 40.058 [salts— (c.c. N/10 NaOHX -0040058)] , . o ^.^ ^ 

 ^ ~ c.c. N /lO NaOH X ■ 0040058 + 18 • 01 b 



10000 [salts— (c.c. N/10 NaOHX .0040058)1 , ,^, ^,,. 



m = XT /i» XT /XTT + 18. 016 



c.c. N/10 NaOH 



Blank determinations should be run with every new lot of re- 

 agents, both by distillation (Reichert-Meissl number) and by 

 evaporation of the titrated portion (salts), and deducted in the 

 calculation. To check the N/10 solution a definite quantity 

 should be evaporated with an excess of sulfuric acid and cal- 

 cined. If the weight obtained is greater than the alkali con- 

 verted to sulfate, due to impurities, the factor .0040058 should 

 be increased sufficiently to offset it. 

 Limit of error, 1 molecular weight. 



1 UsinfT X/10 Bodium hydrate, prepared from caustic alkali made from metallic sodium 

 so as to insure freedom from impurities. 



