Two important methods deal with the trapping and weighing of products in the solid and gaseous phases. The first of these falls into the category of a precipitation method. Many metallic elements in their ionic forms react with negative counter ions to produce stable precipitates. Silver ions form stable and highly insoluble salts with chloride, bromide and iodide. Calcium precipitates quantitatively with oxalate and can be measured reproducibly at any of three temperature dependent plateaus as the oxalate, the carbonate and the oxide.
Barium precipitates quantitatively as the sulfate.
An interesting volatilization method which is entirely gravimetric is the one shown by the equations below. The analyte can be bicarbonate as shown or a mixture of carbonate and bicarbonate. The total amount of carbonate in whatever form is found by placing the analyte in a solution containing an excess of H 2 SO 4 . The apparatus is shown below. Note that the nitrogen gas acts only as a carrier and does not take part in any reaction.