SCIENTIFIC SUMMARY. 
273 
tubs, with an equal weight of boiling water, and well stirred, a good deal 
of nitrous acid being given off ; it is then left standing for twenty-four hours. 
The residue is then washed, etc., and treated afresh with boiling water. 
The first decanted liquid is, when cool, precipitated by hydrochloric acid 
in excess, and the subsiding precipitate is impure chloride of thallium. 
This is washed and dried, and is obtained in the proportion of 68 pounds 
to every three tons of dust. In the next step of the process, the impure 
chloride is converted into a sulphate, and this is then, by hydrochloric 
acid, thrown down as pure chloride. This is now reconverted into the 
sulphate, which is obtained as a white crystalline mass, that evolves much 
heat on being placed in water. Even now it is not sufficiently pure, and 
must be re-crystallized, a little hydrosulphuric acid having been first added, 
in order to throw down any arsenic, mercury, &c., which may be present. 
The best method of obtaining the metallic substance is by precipitation 
with zinc plates. “ Plates of pure zinc (which must leave no residue what- 
ever when dissolved in sulphuric acid) are arranged vertically round the 
sides of a deep porcelain dish, holding a gallon. About seven pounds of 
crystallized sulphate of thallium are then placed in the dish, and water 
poured over to cover the salt. Heat is applied, and in the course of a few 
hours the whole of the thallium will be reduced to the state of a metallic 
sponge, which readily separates from the plates of zinc on the slightest 
agitation. The liquid is poured off, the zinc removed, and the spongy 
thallium washed two or three times. It is then strongly compressed 
between the fingers, and preserved under water until it is ready for fusion.” 
The latter is effected by placing the metal in lumps in an iron crucible, 
fixed over a gas-burner, and which is so arranged that a constant stream 
of coal-gas blows into its upper portion. The molten metal is then stirred 
up with an iron rod, and may be obtained in either the granulated or ingot 
form.— See the Chemical News , October 3rd. 
Forms of Pyrites used on the Tyne in the Manufacture of Sulphuric Acid.— 
Such is substantially the title of a paper read by Mr. J. Pattinson, before 
the British Association, at its Newcastle meeting. Up to 1856, the only 
supplies of this mineral were derived from local sources, from Cornwall 
and from Ireland; but since that period supplies have been obtained from 
Norway, Sweden, Tuscany, Spain, Portugal, Belgium, and Westphalia. 
The quantity of pyrites consumed in this single locality is enormous, 
amounting as it does to seventy thousand tons per annum, or, in a monetary 
aspect, to an expenditure of £105,000. The subjoined table indicates the 
respective value in sulphur of each form : — 
Form of Pyrites. Per-centage of Sulphur* 
1. From Huelva in Spain, and Algarve in Portugal 49*30 
2. From the Rocheux mine, Theux, near Spa 45*0l 
3. Westphalian * 45*60 
4. Norwegian, from the Island of Hitteren 46*50 
5. Irish, from the Wicklow mines 44*20 
6. Coal brasses, from the Walker colliery 38*10 
Minerals and Salts of Coal Pits * — According to the researches of Messrs* 
Clapham and Daglisb, the minerals found in coalpits are not given in 
