Graphs are presented to show the effects of concentration of formaldehyde, pH, time, and temperature on the amount of recoverable formaldehyde remaining in combination with casein after exhaustive washing of the reaction product with distilled water. The results are compared with related data of other investigators and are discussed in terms of possible reactions of various structural units in the protein. The analytical procedures employed for distillation and titration of recoverable formaldehyde were extensively studied and improved. Experiments are also described that show appreciable conversion of formaldehyde to the nonrecoverable form in the presence of casein at 100' C. and above.HE prevailing use of formaldehyde as a hardening agent in T the manufacture of plastics and textile fiber from casein makes it important to know the extent to which formaldehyde is bound by this protein under various conditions. Immersion of casein or other protein in a solution of formaldehyde leads to combination of the latter with varying degrees of stability, which are not easy or possible to distinguish quantitatively. Nevertheless, the formaldehyde taken up by the protein can be classified as to (a) whether it is in sufficiently loose form to be dissipated by washing with cold water or by exposure to air, or (a) whether it is held firmly enough to resist prolonged washing. Measurements of the total amounts of formaldehyde taken up by proteins or allied materials while in equilibrium with the formaldehyde bath obviously include formaldehyde bound in both manners. Such studies have provided valuable information concerning amino acids as well as proteins. Carpenter %nd Lovelace (9) have reported data for casein which represent the difference between the original and final formaldehyde concentrations of the treating bath. On the other hand, the formaldehyde responsible for improved properties in plastics and fibers must be the fraction retained under ordinary conditions of use-that is, the more firmly bound. The formaldehyde content of collagen, washed or pressed free of the loosely held material, has been extensively studied (15) by Highberger and co-workers and by 'Theis and associates, who employed distillation with acid to 'liberate the aldehyde.The work reported in this paper was undertaken to determine the effects of the four major factors-concentration, pH, time, and temperature-on the amounts of formaldehyde firmly bound by casein, and, if possible, to correlate the results with amino acid composition. Nitschmann and Hadorn (17) have reported data on the effects of time and concentration but no series of results showing the effects of pH or temperature.tein selected was a high quality acid casein obtained commercially and ground to pass a 60-mesh screen. Preliminary experiments showed that particle size had a negligible effect over the range studied (40 to 150 mesh).. Air-dried casein equivalent to 2.00 grams on the dry, ash-free basis was added t o 100 ml. of the buffered aqueous solution of formaldehyde in a large tes...
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