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EDTA (ethylenediaminetetraacetic acid) is a weak organic acid.  When the sodium salt is applied  to boiler feed water at a relatively high pH it is hydrolyzed to an organic anion able to form stable soluble organometallic complexes. Calcium, magnesium, iron and copper, metals that normally form troublesome deposits on boiler surfaces, remain in solution when chelated.

The main purpose for determining copper in industrial water is an indication of corrosion somewhere in the system. Chemical factors that cause corrosion of the copper alloys include low pH, ammonia, cyanides, hydrogen sulfide, sulfur and compounds. Although the corrosion rates of copper alloys in industrial waters are usually not high enough to produce significant degradation of the copper components themselves, dissolved copper can cause other operational problems.

Chromium (Total)

Hexavalent chromium (Cr. vi) is an effective corrosion inhibitor in aqueous systems. Trivalent chromium (Cr. iii) is not an effective corrosion inhibitor. In open recirculating cooling water systems, contamination by reducing agents, such as hydrogen sulfide will reduce the hexavalent chromium to trivalent chromium, destroying effectiveness as a corrosion inhibitor.

Chromates are amongst the most widely used chemicals for the control of corrosion in industrial cooling water systems. However, only the chromate or hexavalent form of chromium salts functions as a corrosion inhibitor; trivalent chromic salts do not inhibit corrosion. Chromates are anodic inhibitors and as such, can intensify pitting if used in insufficient concentrations to completely prevent corrosive attack.

The test for chlorine is a test for the hydrolysis products of chlorine gas in water. Chlorine gas is soluble in water, forming hypochlorite ion and hypochlorous acid.

The chlorides of calcium, magnesium, sodium iron and other cations normally found in water are extremely soluble. Since no precipitation occurs, the chlorides present in boiler and cooling waters are usually proportional to the cycles of concentration.

In industrial water conditioning, the principal application of the chloride test is in the control of blow-down in boiler and cooling systems.

 

Carbon dioxide exists in aqueous solutions as “free” carbon dioxide and in the combined forms as carbonate and bicarbonate ions. “Free” carbon dioxide refers to the uncombined dissolved gas. Its presence in solutions is due either to absorption from the atmosphere or to the decay of organic matter.