346. Saponification Equivalent.—Allen defines the saponification equivalent as the number of grams of fat saponified by one equivalent, viz., 56.1 grams of potassium hydroxid.[311] The saponification equivalent is readily calculated from the saponification value using it as a divisor and 56100 as a dividend. Conversely the saponification value may be obtained by dividing 56100 by the saponification equivalent. No advantage is gained by the introduction of a new term so nearly related to saponification value.
347. Saponification Value of Pure Glycerids.—The theoretical saponification values of pure glycerids are given in the following table.[312]
| Name. | Symbol. | Molecular weight. | Saponification value. |
|---|---|---|---|
| Butyrin | C₃H₅(O.C₄H₇O)₃ | 302 | 557.3 |
| Valerin | C₃H₅(O.C₅H₉O)₃ | 344 | 489.2 |
| Caproin | C₃H₅(O.C₆H₁₁O)₃ | 386 | 438.3 |
| Caprin | C₃H₅(O.C₁₀H₁₉O)₃ | 554 | 305.0 |
| Laurin | C₃H₅(O.C₁₂H₂₃O)₃ | 638 | 263.8 |
| Myristin | C₃H₅(O.C₁₄H₂₇O)₃ | 722 | 233.1 |
| Palmitin | C₃H₃(O.C₁₆H₃₁O)₃ | 806 | 208.8 |
| Stearin | C₃H₅(O.C₁₈H₃₅O)₃ | 890 | 189.1 |
| Olein | C₃H₅(O.C₁₈H₃₃O)₃ | 884 | 190.4 |
| Linolein | C₃H₅(O.C₁₈H₃₁O)₃ | 878 | 191.7 |
| Ricinolein | C₃H₅(O.C₁₈H₃₃O₂)₃ | 932 | 180.6 |
| Euricin | C₃H₅(O.C₂₂H₁₄O)₃ | 1052 | 160.0 |
From the above table it is seen that in each series of glycerids the saponification equivalent falls as the molecular weight rises.
348. Acetyl Value.—Hydroxy acids and alcohols, when heated with glacial acetic acid, undergo a change which consists in substituting the radicle of acetic acid for the hydrogen atom of the alcoholic hydroxyl group. This change is illustrated by the equations below:[313]
For a Fat Acid:
| Ricinoleic acid. | Acetic anhydrid. | ||
| C₁₇H₃₂(OH).COOH | + | (C₂H₃O)₂O | = |
| Acetyl-ricinoleic acid. | Acetic acid. | ||
| C₁₇H₃₂(O.C₂H₃O)COOH | + | HC₂H₃O₂. | |
For an Alcohol:
| Cetyl alcohol. | Acetic anhydrid. | ||
| C₁₆H₃₃.OH | + | (C₂H₃O)₂O | = |
| Cetyl acetate. | Acetic acid. | ||
| C₁₆H₃₃.C₂H₃O | + | HC₂H₃O₂. | |
Determination.—The method of determining the acetyl value of a fat or alcohol has been described by Benedikt and Ulzer.[314] The operation is conducted on the fat acids and not on the glycerids containing them.