Wurster, C. Paper testing. Papier-Zeitung 13: 411 (1888); J. Soc. Chem. Ind. 7: 338.
It has often been stated that the cause of paper becoming brittle or tender is to be found in the presence of alum or aluminum sulfate in the paper. The author's observations, extending over 10 years, tend to the conclusion that neutral or basic aluminum sulfate exercises no decomposing influence at ordinary temperatures on paper, whether size be present or not, but that aluminum sulfate has a strongly caustic action if chlorides, such as those of sodium or calcium, be present, especially at higher temperatures. In this case an injurious action on the paper arises from the formation of aluminum chloride or free hydrochloric acid, which act by abstracting hydrogen, or the elements of water, from the cellular substance.