Semi-opacity and opacity are usually produced by the addition to the glass-mixtures of materials which will remain in suspension in the glass, such as oxide of tin, oxide of arsenic, phosphate of lime, cryolite or a mixture of felspar and fluorspar.
Monazite, a phosphate of thorium and other rare earths, contains on the average about i cc. per gram.
The centre of the quarries is Dunnellon in Marion county, and pebble phosphate is found in Hillsboro, Polk, De Soto, Osceola, Citrus and Hernando counties.
In 1906 was opened a continuation of the line from Pont du Fahs to Kef and thence southwest to Kalaat-es-Senam, a place midway between Kef and Tebessa, the centre of the Algerian phosphate region.
In the yield of gypsum, phosphate rock and salt the United States leads the world.
The same reaction is made use of in the quantitative determination of magnesium, the white precipitate of magnesium ammonium phosphate being converted by ignition into magnesium pyrophosphate and weighed as such.
Phosphorus is obtained as a soluble phosphate (which can be examined in the usual way) by lixiviating the product obtained when the substance is ignited with potassium nitrate and carbonate.
The first mode of occurrence is of little significance practically, for the crystalline rocks generally contain too little phosphate to be valuable, though occasionally an igneous rock may contain enough apatite to form an inferior fertilizing agent, e.g.
Lithium phosphate, Li 3 PO 4, obtained by the addition of sodium phosphate to a soluble lithium salt in the presence of sodium hydroxide, is almost insoluble in water.
Sodium phosphate and sulphate are cholagogue purgatives and are used in the treatment of gallstones.