The oxide of lead, which had been deprived of its arsenic acid by
the potash, was then dissolved in nitric acid, and precipitated by
sulphate of soda in the state of sulphate of lead, from which the
quantity of lead in the ore proved to be 69%— per cent.
Mr. Gregor has found only one specimen in which the proportion of lead to the acid was materially different. In this instance the oxide of lead was “'45, and the acid 23'88, instead of being, as before, 69-: and 2613,.
Beside these ingredients, the ore also contains a portion of mu- riatic acid; and the author has also detected small but variable pro- portions of iron and silica.
The quantity of muriatic acid was ascertained by solution of the ore in nitric acid, and precipitation as usual by nitrate of silver. But Mr. Gregor found it necessary to take certain precautions; for if the solution be made with much heat, part of the muriatic acid is lost by boiling; and if the solution be too concentrated, an arseniate of silver is precipitated along with the muriate, and will then require to be separated, either by solution of it in nitric acid, or by means of its insolubility in pure ammonia, which dissolves the muriate.
In order to determine decisively the nature of the principal acid present in this ore, Mr. Gregor decomposed a portion by sulphuric acid, and, after evaporation of the fluid poured ofi‘, reduced a part of the acid upon charcoal. Part was dissolved in water, and precipitated titanium from sulphate of titanium; part was neutralized with soda. and occasioned a brick-coloured precipitate from nitrate of silver, and a reddish yellow precipitate from nitrate of mercury.
From the whole of the experiments detailed in the paper, the au- thor concludes that lOO parts of the ore contain 69'76 oxide of lead, 26-40 arsenic acid, 1'58 muriatic acid; and that the silica and oxide of iron are not essential to its composition.
The fish described in this account was caught in a herring-net at Hastings, from whence such parts as were more particularly deserving of notice were brought to London for further examination.
It was a male, thirty feet six inches long, and nine feet broad, from the tip of the dorsal fin to the middle line of the belly.
The skin was of a light slate-colour, and though as rough as a new file in the direction from the tail to the head, yet as smooth as satin in the opposite direction.
The mouth was about five feet wide, with six rows in each jaw of small conical teeth, rather curved inwards.
The nostrils were placed on the edge of the upper lip.
The eyes very small, with pupils perfectly round.
