Gravimetric analysis involves determining the amount of a substance by measuring its mass. There are two main types: precipitation methods where the analyte is converted to an insoluble precipitate, and volatilization methods where the analyte or its decomposition products are volatilized. An example precipitation method determines calcium content in water by precipitating calcium as calcium oxalate, then igniting to form calcium oxide and weighing. Precipitates must have known composition after drying or ignition to calculate results from their weight.