formaldehyde - Sciencemadness Dot Org

35*2 FORMA LDEH \ 'DK
chloride "litho" films for photolithography. Where maximum contrast
and emulsion hardness are prime requisites, as in the photolithographic
half-tone reproduction processes, the formaldehyde-hydroquinone-sulfite
developer* are in common use. Willcock 46 summarizes the case for developers
containing formaldehyde and points out that they have characteristics
which are considerably different from those energized by direct addition
of sodium or potassium hydroxide. Dry powder mixtures which may foe
dissolved in water to give "litho" developers, of this type require the use of
paraformaldehyde. However, such compositions are not completely
satisfactory because of the difficulties encountered in dissolving this polymer,
as well a? the troublesome polymerization of formaldehyde in the
highly alkaline solutions. Mnehler 3 - claims that a mild acid, preferably
boric acid, or a buffering salt will prevent the slow polymerization.
The use of formaldehyde-bisulflte combinations as both preservatives
and accelerators for photographic developing solutions was described in 1889
by Schwartz and Mercklin 83 . The sulfite reaction is reversible and in the
presence of a strong alkali, such as sodium hydroxide, proceeds as shown
below unxil equilibrium is attained.
XaSOa-CHsOH 4- XaOH ^ XasSOa 4- CH20 -h H20
Recently Donovan and Wadman 15 patented dry powder developing compositions
comprising hydroquinone, a buffer salt, and formaldehydebisuLfite.
Special developers are sometimes produced by combining known developing
agems wlih formaldehyde and its derivatives. Luttke and Amdt 27
condensed p-aminophenol developing agents with formaldehyde and
acetaldehyde in the presence of potassium bisulfite and reported that the
new agents possess greater developing action than ordinary p-aminophenol
developers. Paris 54 combined hexamethylenetetramine with pyrogallol,
pyrogallol-nxonomethyl ether or methyl-pyrogallol-monomethyl ether,
obtaining crystalline complexes easily soluble in alkaline solutions. The
solutions were stated to be more resistant to aerial oxidation than the
parent pyrogallol.
The hardening action of formaldehyde on the gelatin of photographic
emulsions permits high temperature development to be carried out. To
prevent excessive hardening which retards development by slowing penetration
of the developer, Agnew and Renwick 5 first bathe the film or plate
in a solution containing formaldehyde and a relatively high concentration
of sodium sulfate or disodium orthophosphate, For high-temperature
development, Perutz 33 adds 10 to 20 grams of hexamethylenetetramine per
liter of developer. Gevaert 17 adds hexamethylenetetramine to developers
to counteract the action of "blue-black" agents already present in the
emulsion to be developed or also present in the developer itself.