SAPONIFICATION EQUIVALENT. 325 



alkali required for saponification ; this, multiplied by 0"02805, 

 will give the weight as alkali calculated as potassium hydroxide, 

 KOH ; and the figure thus obtained multiplied by 1,000 and 

 divided by the weight of fat taken will express the " potash 

 absorption " as milligrammes of KOH per gramme of fat. It is 

 also advisable to calculate the "saponification equivalent" (a 

 term due to Allen), which is really an expression of the mean 

 molecular weight. This is calculated from the number of cubic 

 centimetres of normal acid, the definition of a normal solution 

 being that it contains, or is equivalent to, in 1 litre a weight 

 in grammes equal to the equivalent of a substance. It is, there- 

 fore, necessary to calculate the weight of fat which would be 

 saponified by alkali equal to 1 litre of normal hydrochloric acid. 



Let W = the weight of fat taken. 



And V = the number of cubic centimetres of semi-normal 

 . hydrochloric acid equivalent to the alkali required for saponifi - 

 cation. Then the saponification ei|uivalent is expressed by 



2 ,000 W 

 V ■ 



The relation between " potash absorption (K) and '" saponi- 

 fication equivalent " (S) is expressed by the formula 



^ ^ .-.(i.lOO 

 ' " K ■ 



Instead of a pipette, the alcoholic alkali may be measuieil 

 from a burette or automatic measurinji apparatus, and the 

 saponification may \h' conducted in a closed tlask. An open 

 flask or basin should not be used, as ethyl liutyrate, an inter- 

 mediate product of saponification (p. 43), is volatile : this 

 would cause a low value to be obtained. 



According to Kcettstorfer, the potash absorption varies from 

 221 '5 to 233 '0 in genuine butters, with an average of i'll-O. 

 His experience has been contiruied by numerous observers, 

 and the limits have been extended "218 to 235. The saponifi- 

 cation equivalent varies from 253'3 to 'JIO'^. the averau'e being 

 247 1. 



Other ods and fats have a potash absorption of IHO to 199. 

 with an average of about 19.') ; or a saponification equivalent 

 of 295-3 to -IS-iv, with a mean of 287-6. 



Coco-nut and palm-nut oils yield, however, figures which are 

 very different, 246-2 to 268-4. 



Estimation of the Baryta Value — Ave-Lallemant's Method. 

 — Two grammes of butter-fat are saponified as in the Kcettstorfer 

 process, and the solution after neutralisation is evaporated to 

 drvnes'i. 10 c.c. of water is added, and the evaporation con- 

 tinued to nmove the last traces of alcohol. The residue is 



