1909.] PUBLIC DOCUMENT — No. 31. 129 



Supplcvicntary Notes. — As this method is only an arbitrary 

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

 as laid down if comparative results are to be obtained, and by 

 so doing over 90 per cent, of the soluble acids in butter can be 

 secured in the distillate. Repeated distillation yields higher 

 results, but is accomi3anied by decomjjosition of non-volatile 

 acids. 



Butyric, caprivic, caprylic and capric are the only fatty acids 

 that can be distilled under ordinary pressure without decompo- 

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

 current of steam. 



]\Iost 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 j)orpoise, dolphin, croton, cocoanut and palm nut oils. 



(a) Mean Molecular Weight. 

 The titrated volatile acids ^ resulting from the determination 

 of the Reichert-Meissel number are evaporated in a tared plati- 

 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 molecular weight (m) can be readily calculated by the 

 following formula : — 



40.058 [salts— (c.c. N/10 NaOH X 0040058)] 

 ™ ~ c.c. N/10 NaOH X • 0040058 + 18 ■ 01 b 



10000 [salts — (c.c. N/10 NaOH X .00^0058)] 



lU = X^ /,^ XT /^^TT I lo.UlO 



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 X/lO 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 Using N/IO sodium hydrate, prepared from caustic alkali made from metallic sodium 

 so as to insure freedom from impurities. 



