SODIUMMETASILICATE.PDFVIP

FOUR CRYSTALLINE HYDRATES OF SODIUM METASILICATE Cnpsren L. Bnrpn, H. TBvNn,q.uWoonwanl aNo Anoll Pansr A number of compounds of the general formula Na2SiOanHzO are reported in the literature. P. Grothl gives crystallographic measurements for NasSiOs9H2O, described by Fritzsche;2 NazSiOa.8H2O, described by von Ammon;3and NarSiOr5H:O, de- scribed by Peterson.a Erdenbrechet reports the following: NaaSiOs.9H2O,rhombic, melting point 47o C.; NazSiOa6HrO, monoclinic,melting point 62.5oC.; and NazSiOr4H2O,*rexagonal, melting point 85o C. Harman,6 from a study of tfre system NazO- SiO2-HzO at 25 C., claims to have identified by Schreinemakes residuemethod the following compounds:Na:SiOa9HzO, NazSiOs .6H2O, NazSiOs2_1/2IJIO,and NazSiOaThe work of other in- vestigators who have found some evidence of hydrates up to 14 is summarized by James G. Vail.7 In the present work crystals have been prepared of sufficient size and perfection to enablepositive identification of the nine, eight, six and five hydrates of sodium metasilicate. Melting points, densities, photomicrographs, optical properties and crystallographic meastire- ments for these four crystals have been obtained. PnoPanerroN or CnYsr-a.r,s In the preliminary work a seriesof solutions were prepared covering a wide range of Na2O,SiO2, H2O compositions.These were protected from the air and allowed to stand at room temperature on a table pro- tected from vibration. After a period of time crystals would form, usually as massesof very minute individuals. These were drained as dry as possible and centrifuged in a high speed laboratory machine In every case the crystals were analyzed for chemical composition and examined microscopicallyas a means of identification. Out o