38 ESSAYS AND OBSERVATIONS 



efFe<fl of Iron contained in the prefent 

 marie. Iron in ore difcovers none of its 

 metallic properties, and confcquently 

 is not then foluble in any of the acids *. 



But 



• From a ]ate obfervation, I hare fome reafon to 

 doubt the truth of this aflertion. Whilfl; I was exami- 

 ning ^ome ihell-marle, the following unufual appearan- 

 ces occurred to me during its effervefccnce with the mu- 

 riatic acid : A pungent fulphureous vapour ftruck the 

 nofe; when the efFervefccnce was at an end, the acid 

 had acquired a peccliar difagreeable ftyptic tafte, re- 

 fembling thetalle of the /;/;i7ar«»!f«r///. Upon the ad- 

 dition of an alkaline fait to this liquor, when filtered, 

 an okrey film rofe to the furface, and a brown coloured 

 powder fell to the bottom. Having re-diflblved part of 

 this precipitated powder in the acid of fea fait, I added 

 to the folutlon fome drops of the tinclure of galls. Jn- 

 ftantly a deep black colour was produced by the mix- 

 ture. The cxiflence of iron in the marie under exami- 

 nation being thusdemonflrated, I wanted to know what 

 proportion of that metal was contained in this fubftance. 

 lor this purpole, having mixed 50 drops of the acid of 

 fea fait with 120 drops oi pure water, I diffolved ia 

 this mixture ten grains of the precipitated powder above 

 mentioned; confcquently 17 drops of this folution con- 

 tained a grain of the powder. Into 12 ounces of water 

 were put feven drops of this folution. In an equal 

 quantity of the fame water was diffolved i grain of pure 

 faltoffteel. To each of thefe wer? added 40 drops of 



a 



