Phosphoric acid insoluble salts

Inorganic Methods. Before the development of electrolytic processes, hydrogen peroxide was manufactured solely from metal peroxides. Eady methods based on barium peroxide, obtained by air-roasting barium oxide, used dilute sulfuric or phosphoric acid to form hydrogen peroxide in 3—8% concentration and the corresponding insoluble barium salt. Mote recent patents propose acidification with carbon dioxide and calcination of the by-product barium carbonate to the oxide for recycle. 

Reactions in aqueous phase are similar to those of barium chloride. When treated with sulfuric acid, hydrofluoric acid, phosphoric acid or oxalic acid, the insoluble barium salts of these anions are formed. Similarly, many insoluble barium salts may form by double decomposition reactions when treated with soluble salts of other metals. 

Barium hydroxide decomposes to barium oxide when heated to 800°C. Reaction with carbon dioxide gives barium carbonate. Its aqueous solution, being highly alkahne, undergoes neutrahzation reactions with acids. Thus, it forms barium sulfate and barium phosphate with sulfuric and phosphoric acids, respectively. Reaction with hydrogen sulfide produces barium sulfide. Precipitation of many insoluble, or less soluble barium salts, may result from double decomposition reaction when Ba(OH)2 aqueous solution is mixed with many solutions of other metal salts. 

It is most conveniently prepared by adding carbonate of soda to the solution of acid phosphate of lime, obtained by treating bene earth with sulphuric acid. The liquor should be maintained at a boiling temperature and the carbonate of soda must be added as long as effervescence continued, or until the solution has an alkaline reaction. The effervescence is duo to the escape of carbonic acid tbe soda unites with the free phosphoric acid and with a portion of the add of the superphosphate, while at the same time phosphate of lime, or a mixture of this and carbonate of lime, is precipitated. This insoluble matter is removed by filtration, and the liquor is then boiled down and allowed to crystallize. To obtain an additional quantity of the salt from tbe motheT-liquors, it is neocssaiy first to examine if these, manifest an acid or an alkaline reaction. In the first case, more carbonate of soda must he added to restore the alkaline reaction, and the liquor again evaporated and sot aside to crystallize. 

Caffeine, free-base form (water-insoluble) Phosphoric acid Caffeine-phosphoric acid salt (water-soluble) ... 

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