530

ADDENDA.

^ 3. Phftcal and Chemical Properties.

Pure cerium does not appear to have beenyet obtained in the metallic form; in Klaproth ’sexperiments the oxyd when inclofed in a char-coal crucible, and fubjected to the intenfe heatof a porcelain furnace underwent no alteration.Vauquelin, however, by mixing the tartrite ofcerium with a little oil, lamp-black and boraxfucceeded in obtaining a few minute globulesof a metallic appearance, which appeared to bean alloy of cerium and iron.

The precipitate from any of the falts ofcerium by means of a cauftic alkali is the metalin its 'owefVftate of oxydation. Its colour iswhite; by expofure to the air it acquires ayellowifh tinge in its progrefs towards the dateof perfeCt oxyd, but as it abforbs at the fametime carbonic acid it cannot by this procefsarrive at its ultimate term of oxydation. Whenexpofed to the blow-pipe it pafles rapidly intoperfeCt oxyd, and acquires a reddifli-browncolour, but undergoes no further change.When mixed in fmall proportion with borax itforms a greenifh-yellow tranfparent globule,which, by the exterior flame, becomes blood-red, and by long continuance of the interiorflame becomes colourlefs.

The fixed alkalies when digefted with heaton the brown calcined oxyd change its colour towhite, and bring it to the lowed term of oxyd-ation, but do not difiolve any of it. Ammoniahas a fimilar effect on the uncalcined oxyd.

Sulphuric acid, diluted with four times itsweight of water and digeded on the per-oxydof cerium fird communicates to it a brilliantcrydalline appearance, and at length, if the acidis confiderably in excefs, forms a completefolution of it: this folution, by very gentle eva-poration, depofits minute orange coloured crys-tals, fparingly foluble in water, and of a fweetacidulous tade. If the carbonat or fub-oxydof cerium, is employed, the refult is a very palerofe coloured folution which cryftaHizxs with-out difficulty: this latter fulphat contains noexcefs of acid, and has merely a faccharinetade. The fume fait may be produced by-double affinity 4 if fulphat of foda is added tothe nitrat or muriat of cerium a crydalline pre-cipitate falls down, which is the fait in quedion.

Nitric acid, affided by heat, diffoives eafilyeither of the oxyds, forming a yellow folution,which cannot be made to crydallize ; the faithowever may be obtained by gentle evaporation.It has a fomewhat pungent faccharine tade •, isfoluble in twice its weight of alcohol, and when

expofed to heat it melts, is decompofed, and abrick-red oxyd remains behind.

Muriatic acid when digeded on the per-oxyd of cerium exhales an abundance of oxy-muriatic acid gas ; the oxyd is by degrees dif-foived, forming a pale rofe coloured folution,which, when evaporated to the confidence ofa thick fyrup, depofits a confufed mafs of crys-tals. This muriat has a fweetifh flavour, isfoluble in three or four times its weight ofalcohol, and when decompofed by dry didiila-tion, there comes over oxymuriatic acid, and awhite fub-oxyd of cerium remains in the retort.

Any of the preceding falts are decompofableby the alkaline carbonats, fuccinats, phofphats,tartrites and oxalats forming white precipitates,the properties of which have not yet beeninvedigated.

Neither tinfture of galls nor hepatic waterproduce, any decompofition of the above falts ofcerium, but the liquid alkaline hydro-fulphuretsthrow down a yellowifh-white precipitate ; andpruffiat of potafh a milk-white one, providedno iron is prefent.

No ufe whatever has been made of ceriumin any form.

SCHORL, (omitted by miftake in its properplace). Tourmaline. Cockle of the Cornijhminers.

Werner divides this mineral into two fub-fpecies, one of which he calls the black and theother the electric fchorl. But as both of themare electrical, and as the differences betweenthem are very trivial, we have thought bed tofollow the example of Hauy, and confiderthem as forming only one fpecies.

The colour of this mineral is greyifh-white ;leek, olive, and pidachia green; liver-brown,yellowifh and reddifh-brown; hyacinth-red,crimfon-red•, victlet-blue, fky and indigo-blue •,velvet-black. It occurs in mafs, diffeminated,in rolled pieces and crydallized. Its primitiveform is an obtufe rhomboid, the larger planeangles of which meafure 113 0 34 4i". TheaCtual forms that it prefents are the following.

1. A nine-fided prifm, terminated at oneextremity by fix, and at the other by threefacets. Of the fix facets, three are hexagons,

-and three triangles.

2. A twelve-fided prifm terminated at eachextremity by the fame . number of facets as thepreceding. Of the fix facets, three are hepta-gons, and three trapeziums.

3. A nine-fided prifm, terminated by thefame number of facets as the preceding. Of