FLUOR SPAR. 123 



beautiful. The mineral is difficult to work on account of be« 

 ing brittle. It is usually turned in a lathe, and worked down 

 first with a fine steel tool ; then with a coarse stone, and 

 afterwards with pumice and emery. The crevices which 

 occur in the masses are sometimes concealed by filling them 

 with galena, a mineral often found with the fluor. Fluor 

 spar is also used for obtaining fluoric acid, which is employed 

 in etching. To etch glass, a picture, or whatever design it 

 is desired to etch, is traced in the thin coating of wax* with 

 which the glass is first covered ; a very small quantity of the 

 liquid fluoric, acid is then washed over it ; on removing the 

 wax, in a few minutes, the picture is found to be engraved on, 

 the glass. The same process is used for etching seals, and 

 any siliceous stone will be attacked with equal facility. Fluor 

 spar is also used as a flux to aid in reducing copper and 

 other ores, and hence the name jluor. 



Hayesine or Hydrous Borate of Lime. Occurs in snowy white inter- 

 woven fibers, with gypsum and alum on the plains of Iquique, S. A. 



Hydroboracite. A hydrous borate of lime and magnesia resembling 

 somewhat a white fibrous gypsum. It is of Caucasian origin. 



Oxalate of Lime. Observed on calc spar in small oblique crystals. 

 Locality unknown. 



Nitrate of Lime. In white delicate efflorescences ; deliquescent. 

 Also in solution in some waters. The salt is formed in calcareous 

 caverns and covered spots of earth where the soil is calcareous. It is 

 extensively used in the manufacture of saltpeter, (nitrate of potash.) 

 Occurs in the caverns of Kentucky and other Western States. 



7. MAGNESIA. 



The sulphates and nitrate of magnesia are soluble, and are 

 distinguished by their bitter taste. The other native mag- 

 nesian salts are insoluble. The presence of magnesia when 

 no metallic oxyds are present is indicated by a blowpipe 

 experiment : after heating a fragment, moisten it with a solu- 

 tion of nitrate of cobalt, and then subject it again to the heat 



How is glass etched by means of fluor spar ? What is the origin of 

 the name fluor ] What is said of the occurrence and uses of nitrate 

 ot lime 1 What is the taste of soluble salts of magnesia 1 What blow- 

 pipe test distinguishes them ? I 



* The best material is a mixture of bees wax and turpentine resin 

 melted together. 



