Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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hydrolysis

In its broadest sense, hydrolysis indicates a reaction between any substance and water; however, the use of the term is commonly restricted to those reactions due directly to the hydrogen and hydroxyl ions of the water. Due to hydrolysis, for example, nearly every salt yields a slightly acid or alkaline solution. Thus, ethyl acetate in water, for example, forms acetic acid and ethanol: CH 3 CO 2 C 2 H 5 , + H 2 O → CH 3M COOH + C 2 H 5 OH.

Hydrolysis is the basis for the manufacture of soap (saponification), whereby fats (glycerol esters of fatty acids) are split with aqueous solutions of sodium hydroxide to form the sodium salt of the fatty acid (soap) and the alcohol (glycerol—more commonly known as glycerine). In reactions involving sal[s, the neutralization reaction that led to the formation of the salt is partially reversed, forming some free acid and free alkali. If the acid is weak, i.e., poorly ionized, and the alkali is strong, i.e., highly ionized, the aqueous solution of the salt will have an alkaline reaction as a result of the hydrolysis.

In the opposite case, that of a strong acid and weak base, the salt will have an acidic reaction in an aqueous solution. An example of the latter is papermaker's alum (aluminum sulfate), which is hydrolyzed in aqueous solution to form aluminum hydroxide (Al(OH)), which is insoluble and therefore forms few ions, and sulfuric acid (H 2 SO 4 ), which is almost completely ionized in a dilute water solution. The acid character of alum is well known by its extremely sour, astringent taste, and by its detrimental effect on the permanence of paper.




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