Of A VARIETY OF THE CORUNDUM. 211 



rectified fulphuric acid upon it, and placed the vefTel in a di- 

 gefting heat. The powder became at firft gelatinous. But 

 this inconvenience was gradually removed, by the further ad- 

 dition of acid. What was diffolved thereby was extracted by 

 difrllled water. 



The earth which remained, after having been fufficiently The laft refidue 

 edulcorated, was dried and expofed to the action of potafh in wh^potafli^aiid 

 a filver crucible as before, and what the potafh difforved was its refidue by 

 added to the alkaline folution before mentioned (A b). What ^f J^f" 

 was undiffolved by it was heated again with fulphuric acid, were added to the 

 until it ceafed to ad upon it. The foluble part was extraaed { ? x ™ r > ar ? d a c 



r ri fmall portion of 



by diftilled water. The refiduum was thrown on a nitre and ( x \ tx remained. 



warned with diflilled water till it ceafed to affect nitrat of 



mercury : dried and heated red hot for half an hour, it 



weighed y gr. It was pure filex. 



The folution effected by fulphuric acid, was mixed with the The fulph. fblu- 



edulcorating water and decompofed by ammonia. A white , tlon was PJ" eci P« 

 /• • •. i TTTi m r , by ammonia, 



ipongy earth was precipitated. When the ammonia cea led i t contained no 



to caufe any further precipitation, the clear decanted fluid was linie * 



affayed with carbonat of ammonia and carbonat of potafh, but 



no change was produced on it by the folution of either of thofe 



falts. From which circumftance the abfence of lime may be 



inferred. 



The precipitate produced by ammonia was fufficiently The warned 

 wafhed with diflilled water, and in a moift date, was boiled * m a £°£^ e d cip " 

 with the folution of potafh in a filver crucible as before. The with pota/h ; ia 

 alkali diffolved a portion of it. Which folution, together P art diffolved. 

 with the edulcorating water, which wafhed the remainder, 

 was added to the alkaline folution before mentioned, (Ab). 

 What remained was thrown on a filtre, and edulcorated as 

 before : dried and heated red hot for ten minutes, it weighed 

 four grains. 



It was of the colour of pounded refin. Expofed to the It left oxide of 

 flame of the blowpipe or charcoal it was unaltered. Moiftened tItan,uin " 

 with melted tallow and ignited, it was not attracted by the 

 magnet. It was taken up by a globule of the phofphat of 

 ammonia and foda, and fufpended in it in white flakes. It is 

 foluble in the three mineral acids. But the folution, on being 

 boiled, becomes turbid from the feparation of a large por- 

 tion of it. It is precipitated from its folution in acids by 



P 2 prufliat 



