212 0F A VARIETY OV THE CORUNDUM. 



prufliat * of potato, of a beautiful grafs-green, and by tinc- 

 ture of galls of a dark orange-colour. It poflefled, in fhort, 

 all the properties of the oxide of titanium. 



The alk. folu- The alkaline folution (Ab) was faturated with muriatic 

 mm. acid and ac '^* ^ co pi° us precipitation took place of a white earth, 

 diflblved ; pre- which was rediflblved by a further addition of acid. The con- 



o/'otafli "and tents °^ ^' s * omt i° n were thrown down by a folution of car- 

 edulcorated, bonat of potafh. This precipitate collected on a filtre, was 



wafhed with diflilled water, till it patted through it taflelefs. 



Dry precip. It was dried and introduced into a matrafs, and rectified 



fubh. d add h left ful P huric acid » diluted with diflilled water, dropped into it, 



filex. and the fluid was evaporated. Frefh portions of acid were 



abflra&ed from it, as long as it feemed to a6t upon it. The 



foluble part was extracted by diflilled water, and the refiduum 



was edulcorated with diflilled water, till it ceafed to produce 



any change upon nitrat of mercury ; dried, and heated red 



hot for half an hour, it weighed 10 grains. It was pure filex. 



This fulph. folu- The folution which the fulphuric acid had effected, mixed 



tion with acet. w ^ t j ie water w j t h wn i c h the refiduum had been edulcorated, 



of potafh gave . 



alum. was gradually evaporated, and a mfficient quantity of acetite 



of potafh was added to it. Regular cryflals of alum were 

 formed to the lafl. A fmall portion of filex, amounting to 

 about | a grain, was feparated. 

 The alum, was Diflilled water was poured upon the alum, in a quantity 

 decomp. by carb. f u ffi c i e nt to diffolve it in a warm flate ; and whilfl warm, the 

 folution was decompofed by a folution of carbonat of ammo- 

 nia. The fpungy earth which was feparated, was collected 

 on a filtre and edulcorated with diflilled water, till it produced 

 no effect upon nitrat of mercury. 



amme-n. 



* The prufliat of potafh which I employed, was prepared by 

 dropping a folution of tartrite of potafh into a folution of prufliat 

 of lime, as long as any tartrite of lime is precipitated. Large and 

 beautiful cryflals of prufliat of potafh are produced by evaporating 

 the fluid, which I have found to remain unaltered for feveral years. 

 By this method the intruflon of the fulphuric acid is prevented : but 

 Mr. Henry's late ingenious procefs feems to be, for many reafons, 

 preferable to it. The prufliat of titanium promifes I think, to be 

 ufeful in the arts. Painters in oil and water colours would find ia 

 it a valuable acquifition, as a beautiful tranfparent green. 



The 



