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This lab has the same procedure as the alkalinity test on water, except it is performed on sludge, which is a little thicker.  So follow these same guidelines when performing your experiment. 

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Alkalinity is a measure of the basic constituents of water.  Basic constituents refer to the constituents causing water to be basic as opposed to acid.  Alkalinity in natural waters is usually due to the carbonate and bicarbonate salts of calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K).  Alkalinity is very important in connection with coagulation and corrosion control, but is of little sanitary significance.  When alum, which is an acid salt, is added to the raw water reacts with the alkalinity present to form floc.  If insufficient alkalinity is present, alkalinity must be increased in order for a good, dense floc to form and to prevent soluble alum from being left in the water.  The added, or artificial, alkalinity is in the form of lime or soda ash.  Not only must sufficient alkalinity be present to complete coagulation, but enough must be present later in the coagulated water to prevent it from becoming corrosive.  Alkalinity can exist as hydroxide, carbonate, or bicarbonate.  In the usual pH range of approximately pH 7 to 8.5 for Alabama waters, the alkalinity consists primarily of bicarbonates and carbonates.