268 VII. EARTHS AND ALKALIES.— 



STONES AND GLASSES. 



The five precious stones. Garnet, hyacinth, sapphire, 

 cornelian, emerald : cordial ! 



Crystal powder. Heat quartz red hot, quench it in water, 

 then grind in an agate mortar, or chert mill ; used in making 

 glass, and is a good dryer for paints. 



Flint powder. Heat flints, quench in water, then grind to 

 powder ; used in making fine pottery. 



Maidstone sand, Arena rotunda. Fine, white, used to dry 

 up ink, and to filter acid and corrosive liquors. — Lynn sand. 

 White, used to make flint glass. 



Sea sand. Coarse ; when washed and dried used for scour- 

 ing, and sand heats. 



Powdered glass, Vitrum pulverisatum. Powdered as crystal, 

 or flints ; used to filter acids ; also glued upon paper as a polishing 

 powder, and to wear down corns upon the feet, after the feet have 

 been well soaked and dried, likewise to blow into the eyes to wear 

 down any excrescence. 



Emery, Smyris, Smerillus, Extremely hard ; ground in mills, 

 and sorted by being stirred with water, the water left to settle for 

 a determinate number of minutes, then drawn off* into another 

 vessel, and left finally to deposit the powder with which it is 

 loaded ; used for polishing, either in the state of powder, or 

 glued upon paper for scouring : emery stones from Jersey and 

 Naxos. 



Pothee d'emery. The sludge that falls from lapidaries' 

 mills, made into balls for polishing. — Moule, The sludge of the 

 grindstones used in grinding cutlery. 



Pierre a l'eau tendre. Greenish or brownish grey, easily 

 rubbed to powder in water, powder used to polish metals. 



Water-of-Ayr stone. Used for polishing mathematical 

 instruments. 



Pumice stone. Lapis pumex, Pumex, Spongy, swims upon 

 water; used whole as a kind of file, in powder as a polishing pow- 

 der, and added to some dentrifices. 



Lancet stone, A green soft hornstone, found in some parts 

 of the old pavement in London : the only known material on 

 which lancets can be set ; said to come from Germany. 



Hone, Pierre a rasoir. Yellow, with a bed of black slate 

 clay, used with oil, but soap is much cleaner ; from Namur. 



1 



