6o6 On the Aerated Barytes. 



New Trial vein, which has hitherto been little 

 worked upon, but where an eflay is now intended 

 to be made. The quantity of it gained in that 

 part of the Sun Veip, where they are now at work 

 is very inconfiderable. 



I purpofely avoid entering into a more minute 

 detail of the various parts of the Mine, of the 

 method of working the Vein, or of fuch other 

 circumftances as might appear neither peculiar 

 nor interefting, and fhall clofe this account with 

 a defcription of the External Characters of the 

 Aerated Barytes i as well for the information of 

 mineralogifts, who have not had an opportunity 

 of feeing it under fo many different circumftances, 

 as for the inftruftion of thofe, whofe bufinefs re- 

 quires that they fhould have a fufficient know- 

 ledge of it, not to confound it with other fofllls.* 



The 



* In a late advertifement for the fale of the MuriatedTerra 

 Tonderofa, it is afTerted, that the mineral from which that 

 Salt is obtained, (meaning the Aerated Barytes) frequently 

 contains a quantity of Arfenic and Lead. If by the word 

 *• contains" be meant a Chemical comh\nzUon. of thefe poi- 

 fonous metals, there is not fufficient ground for the affer- 

 tion ; finc6 the Mineral, fuch as I have defcribed it, con- 

 tains according to the belt analyfes, nothing but Terra Pon- 

 derofa. Fixed Air and fometimes a fmall adventitious quan- 

 tity of Vitriolated Barytes. I have indeed obferved tlvat 

 what has lain a long time in the Old Works in the interior 

 of the mine, becomes penetrated with ochreous water, 

 which infinuating itfelf between the fafciculi, gives a yel- 

 lowifli tinge to the whole. The Aerated Barytes thus con- 

 taining Iron, when expofed to heat becomes green, a cir- 

 cumftance which Fourcroy in a paper on that foffil, in the 



fourth 



