On the RffeEis of "Terra Ponderofa, 6 1 7 



*' I did not exped. Some part of the Barytes 

 " appears to have begun to vitrify with the 

 " matter of the cup in which it was expofed and 

 *f has formed a greenifli fubftance, which fticks 

 *^ pretty faft to the Vefiel and in one place has 

 " corroded it fo much as to have formed a fmall 

 " hole exactly in the way that Fluor does. As 

 ** I was not very careful in picking the pieces 

 " I fuppofe the greenifh colour to have been 

 " owing to fome impurities.* This experiment 

 " has however proved that a long continued heat 

 ** does not expel the v/hole of the fixed air if it 

 " does any part of it, for the burnt Barytes 

 ** immediately upon coming out of the oven 

 " effervefced ftrongly with the Marine Acid and 

 ** diflblved exadly in the fame manner as the 

 ** crude. The heat it has undergone was 110°. 

 " of my Father's Thermometer." 



Finding it was impoflible to render the earth 

 cauftic by this procefs, I defired the above- 

 mentioned Gentleman to make ufe of Dr. 

 Withering's method of dilTolving it in the Ma- 

 rine Acid, precipitating by a mild Alkali, and 

 expelling the fixed air by heat from the artifi- 

 cial Aerated Barytes thus formed. This was 

 done and the earth rendered perfedlly cauftic. 



• The Specimens I fent Mr. Wedgewood were penetrated 

 with ochreous water, therefore I (hould imagine the green 

 colour to proceed from the Iron, 



but 



