of Johnson's Dictionary, 



287 



Mica, in natural history, a genus 

 of talcs. 



NiTRR. [The dictionary here gives 

 a very long and erroneous account 

 of this salt, taken from Hill on 

 FossiU.'\ 



Opal. [Again an absurd definition 

 from Hill's Materia Medica.^ 



Orpiment, a foliaceous fossil, &c. 

 Orpiment has been supposed to con- 

 tain gold, and is found in mines of 

 gold, &c. 



Phosphorus, a chymical sub- 

 stance, which, exposed to the air, 

 takes £re. 



Porphyry, marble of a particular 

 kind. 



Quicksilver. [The dictionary 

 gives a long, and for the most part 

 erroneous detail, from Hill's Ma- 

 teria Medica."} 



Resin, the fat sulphureous parts 

 of some vegetable, which is natural 

 or procured by art, and will incorpo- 

 rate with oil or spirit, not an aque- 

 ous menstruum. 



Selenite, a sort of fossil. 



Mica, a mineral oonpoeed of 

 silica, alumina, potash, and oxide of 

 iron, which occurs massive and crys- 

 tallized: it is easily divisible into 

 thin flexible and elastic laminae, by 

 which it is distinguished from talc, 

 which is not elastic. 



NiTfiE, a salt composed of nitric 

 acid and potassa : nitrate ofpotassa. 



Opal, a gem remarkable for the 

 brilliant display of colours which it 

 exhibits by reflected light. Its 

 analysis affords 90 silex 10 water, i 



Orpiment, a compound of sul- 

 phur and arsenic. It is lamellar in 

 one direction, and of a yellow colour. 



Phosphorus, an undecompounded 

 substance, when pure of the consis- 

 tency and appearance of white wax ; 

 highly inflammable, 'and exhaling 

 acid fumes of an alliaceous smelF 

 when exposed to air. 



Porphyry, a very hard rock com- 

 posed chiefly of feldspar : it takes a 

 fine polish, and is sometimes used 

 for ornamental purposes. 



Quicksilver, or Mercury, a me- 

 tal liquid at common temperatures : 

 at about 600° it boils, and at — Z9° 

 it freezes, becoming a ductile and 

 malleable solid. 



Resin, a fusible and inflammable 

 vegetable product, soluble in alcohol 

 and ether, but insoluble in water. 



Selenite, a variety of crystallized 

 sulphate of lime, having a silky lus- 

 tre : from (TiXwn, the moon. 



[The Editor has taken the liberty to abridge the above ar- 

 ticle, and has only retained a few of the " specimens" trans- 

 mitted by his correspondent ; he has ^so omitted the list of 



