"Specific examples of alkaline buffering salts are the carbonates, bicarbonates, orthophosphates, monohydrogen orthophosphates, pyrophosphates, tripolyphosphates, metaphosphates, silicates having SiO :M O ratios of from about 1 to about 2.6, preferably 1.6 to 2.6, wherein M is an alkali metal, hydroxides, citrates, and acetates of alkali metals, e.g. ammonium, sodium, potassium and lithium, and mix" . . . . .