Borax-alkali buffer

Carbonate and sodium metaborate are the most stable alkalis. Borax does not buffer well against a rise in pH, and hydroxide loses its alkalinity rapidly as the solution is diluted. 

As far as the general composition of superfine grain developers, nearly all of them have a high sodium sulfite content as sodium sulfite is an effective silver solvent. For an alkali, they use small quantities of either carbonate or borax in order to minimize the energy of the developer and produce a finer grain. FX 10 uses a buffering mixture of borax and boric acid, whereas Windisch Superfine Grain Developer uses sodium metabisulfite to reduce the pH of the sodium sulfite. 

When processing at high temperatures a mildly alkaline, buffered borax developer is recommended. Alkali-free developers of the amidol type or one of the mildly alkaline fine grain developers such as Kodak D-23 are preferable to those with normal alkali content. Additionally, a pre-hardening bath such as Kodak SB-4 Tropical Hardener Bath or a specially formulated tropical developer may be used. 

Table II shows results for the electro-oxidation of secondary alcohols and ketones. In alkaline electrolyte, secondary butanol was not oxidized to methyl ethyl ketone but was cleaved to acetate. Similarly methyl ethyl ketone was cleaved to acetate, although some CO2 and propionate formed, indicative of cleavage on the other side of the carbonyl group. Butanediol (2 ) went to acetate yielding less CO2. At pH 9 in borax buffer 2 Trtanol went exclusively to methyl ethyl ketone at 89% conversion, suggesting that enolization in alkali is a necessary part of the cleavage process. Cyclohexanol and cyclohexanone were both converted to adipic acid. Figure 12 summarizes the various types of electro-organic oxidations, thus far discussed, which are observed to occur on lead ruthenate in alkaline electrolyte.

The primary buffer standards — phthalate, phosphate and borax solutions — are prepared by direct solution of weighed amounts in water and dilution to a known volume. Solutions of acid or alkali used in the preparation of buffers should be standardized by titration. Even so, to guard against any inadvertent error, the user is strongly advised to check with a pH meter the pH values of buffer solutions at the temperature for which they are required. 

The element boron forms strong bonds with oxygen. The resultant borates include boric acid, boric oxide, alkali, ammonium, and alkaline earth metal borates. All except for the alkaline earth borates are reasonably water soluble. When dissolved borates release boric acid, a Lewis acid, and its conjugate base, the tetrahydroxyborate anion. Borax, a form of di-sodium tetraborate, releases equimolar amounts of these species and consequently is an excellent mildly alkaline pH buffer. Borates exhibit several important behaviors in solution, including the sequestration of water hardness ions, the ability to form borate esters with polyols, and to deliver the oxidant hydrogen peroxide into solution from the dissolution of sodium perborate. 

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