[200] Unfortunately, the nondescriptive name “aspirin” has been used extensively in European literature and has even got into European pharmacopeias, instead of the scientific name “acetylsalicylic acid.”
[201] For reference to older literature see Beilstein, II, 1496 (889).
[202] “The Melting Temperature of Aspirin and Salicylic Acid Mixtures,” Proc. Assoc. Off. Agr. Chem., 1912; Bureau of Chemistry, Department of Agriculture, Bull. 162.
[203] “Assay of Aspirin,” J. Pharm. Chem., 15 (117), No. 7, 213.
[204] Similar observations were made by Emery and Wright, who state: “An accurate determination of the melting temperature in this way (the rate of heating was such as to give a rise in temperature of about 1° per minute) is rendered difficult by the fact that ‘aspirin’ decomposes on heating, as evidenced in the depression of the melting temperature of the pure substance of about 1° for every five minutes’ heating just below its melting temperature.”
[205] Isolated crystals attached to the walls of the melting-point tube, apart from the bulk acetylsalicylic acid, melted at a lower temperature.
[206] An excess of alcohol destroys or lessens the color when only a very minute amount of salicylic acid is present.
[207] The control should be made each time as standing in the air changes its tinctorial power.
[208] The presence of pure acetylsalicylic acid does not seem to affect the iron (Fe+++) salicylic acid coloration. The small amount of acetic acid was added to the sodium salicylate control solution (1) to stimulate an acidity approximating the acidity of the acetylsalicylic acid, and (2) since acetylsalicylic acid gives by hydrolysis both acetic acid and salicylic acid, it was thought advisable to add acetic acid to the standard. If there is any free acetic acid in a sample of acetylsalicylic acid containing salicylic acid (which I believe is generally the case when salicylic acid is present) then it would modify the color given by the same amount of salicylic acid alone. For this reason it was thought to be more comparable to have the standard contain a slight amount of acetic acid.
[209] This standard is somewhat similar to the one proposed by T. W. Thoburn and Paul J. Hanzlik, J. Biol. Chem., 23, 175.