Half-bound carbon dioxide (CO_{2}) = 0.44 times the bicarbonate expressed in terms of calcium carbonate. NORMAL CARBONATE.[20][94] Normal carbonate is present if the alkalinity to phenolphthalein is greater than zero but less than the alkalinity to methyl orange, erythrosine, or lacmoid. If the phenolphthalein alkalinity is exactly equal to one-half the methyl orange, erythrosine, or lacmoid alkalinity the alkalinity is due entirely to normal carbonate. If the phenolphthalein alkalinity is less than one-half the methyl orange, erythrosine, or lacmoid alkalinity normal carbonate expressed in terms of calcium carbonate is equal to twice the phenolphthalein alkalinity. If the phenolphthalein alkalinity is greater than one-half the methyl orange, erythrosine, or lacmoid alkalinity the normal carbonate is equal to twice the difference between the methyl orange, erythrosine, or lacmoid alkalinity and the phenolphthalein alkalinity. The carbonate, carbon dioxide as carbonate, and bound carbon dioxide can be calculated as follows: Carbonate (CO_{3}) = 0.6 times the normal carbonate expressed in terms of calcium carbonate. Carbon dioxide as carbonate (CO_{2}) = 0.44 times the normal carbonate expressed in terms of calcium carbonate. Bound carbon dioxide (CO_{2}) is the sum of the carbon dioxide as carbonate and one-half that as bicarbonate. HYDROXIDE.[20][94] If hydroxide, or caustic alkalinity, is present the alkalinity to phenolphthalein is greater than one-half the alkalinity to methyl orange, erythrosine, or lacmoid; the alkalinity is due entirely to hydroxide if the phenolphthalein alkalinity is equal to the methyl orange, erythrosine, or lacmoid alkalinity. If the phenolphthalein alkalinity is more than half and less than all the methyl orange, erythrosine, or lacmoid alkalinity, hydroxide, expressed in terms of calcium carbonate, is equal to twice the phenolphthalein alkalinity minus the methyl orange, erythrosine, or lacmoid alkalinity. ALKALI CARBONATES. Waters which contain sodium or potassium carbonates or bicarbonates contain all of their calcium and magnesium as carbonates or bicarbonates. That is, they possess no non-carbonate hardness (sulfates, nitrates or chlorides of calcium and magnesium). The most accurate method is to determine the total alkalinity by titration with N/50 sulfuric acid, using methyl orange, erythrosine, or lacmoid as an indicator; then determine the calcium and magnesium content; and subtract from the total alkalinity the computed alkalinity due to the calcium and magnesium expressed in terms of calcium carbonate. The remainder is the alkalinity due to carbonates and bicarbonates of sodium and potassium. This determination may also be made by applying the method, for non-carbonate hardness with soda reagent (see p. 35), and by noting the excess of acid required to neutralize the alkaline carbonates originally present.