168 ESSAY XII. 



colour ; I dissolved it in water ; the solution was clear and 

 colourless ; to the bottom of the vessel a small quantity of 

 red powder subsided, which, after being dried, weighed 1 1 grs., 

 and proved to be an iron ochre. From the solution I 

 obtained, upon evaporation, both vitriolated tartar and nitre 

 in crystals ; but a good deal of lixivium remained, which 

 refused to crystallise, though there was no mark of super- 

 fluous alkali. I mixed it with a little water, to which I 

 afterwards added diluted acid of vitriol, till there appeared no 

 more precipitation. This precipitate, when edulcorated with 

 lime-water and dried, weighed 3 drms. If too much acid of 

 vitriol is added in the foregoing process, the precipitate will 

 be redissolved, and the water itself retains a part of it in 

 solution. Nay, while the solution is hot, no precipitation 

 ensues. A precipitate is likewise obtained by means of 

 nitrous or muriatic acid. 



SECTION VI. 



In order to become better acquainted with this kind of 

 earth, I first examined that obtained by means of nitrous 

 acid, via humida (Sec. in). 



(a) I reduced 1 scruple of it in a glass mortar to a very 

 fine powder, and boiled it with 2 oz. of distilled water 

 for a quarter of an hour. The 'liquid was then poured 

 into another vessel, and the remainder again boiled with 

 2 oz. more of water, which, when poured off, had a 

 peculiar acid and somewhat metallic taste. I therefore 

 repeated the same process ten times over, always with 2 oz. 

 of fresh water, and found at last that nearly the whole was 

 dissolved. (b) Thinking that perhaps some vitriolic acid 

 might have adhered to the earth, and thus be the cause of its 

 solubility in water, I exposed part of the terra molybdaenae 



