formaldehyde - Sciencemadness Dot Org

USES OF FORMALDEHYDE 337
penetration, the borax is neutralized with an organic acid 1 *. In a process
described by Turley and Somerville 33 , white leather is produced by laiming
hides lightly with formaldehyde and then completing the tannage with an
acidified solution of water-glass.
Blends of formaldehyde with metal tanning agents such as aluminum or
chromium compounds are advocated in some processed 18 * 133 - 3 *. The
addition of formaldehyde to pickle liquor is stated to reduce the chromium
o:dde (Cr20«) fixed and raise the shrinkage temperature of the finished
leather 8 ' 29 . Mason 15 also reports that formaldehyde serves well in combination
with mineral or salt-acid tanning solutions where coloring is to be
avoided. Because of its tendency to form insoluble compounds with vege-
Fig. 27. Finishing of formaldehyde-tanned leather.
table tannins, blends with these agents are apparently not entirely satisfactory.
Neutral synthetic tanning agents are usually compatible.
Although the exact mechanism of formaldehyde tanning is still not
definitely known, it, appears probable that it is the result of the reaction of
leather-collagen with formaldehyde. The general nature of this reaction
has been previously discussed in connection with formaldehyde-protein
reactions (pp. 221—224). Chemical studies of aldehyde tanning indicate
that it is characterized by two reaction types: a rapid reaction involving
free amino groups and a slow reaction involving the amido groups of the
peptide linkages 27 . Cross linkage of these amido groups by methylene
radicals involving contiguous protein molecules is believed by Kizntzel 11
and Theis 31 to be of paramount importance in the production of water re-