134 Progress in Science. [January, 



causing them to act on the upper surface of the molten pig-iron, which is 

 placed in a peculiar syphon-shaped converter. 



Mr. W. Dingley has lately patented the use of sulphate of soda, in the crude 

 state of salt-cake, for the purification of iron. A small quantity of the salt is 

 thrown on to the surface of the molten iron during the operation of puddling 

 — a dose of about 12 ozs. being recommended for each heat of 4 or <±\ cwts. of 

 metal. 



Some improvements in the separation of silver and gold from lead have 

 been announced by Messrs. Risway and Pauville, of Paris. The argentiferous 

 or auriferous lead is treated with magnesium or aluminium, either alone or 

 alloyed with zinc, and the rich scum thus obtained is amalgamated with mer- 

 cury. The inventors state that the)' are able to regenerate the metals which 

 have been used in the process of extraction, and have thus greatly reduced the 

 expense of separating the precious metals from the lead. 



Mr. F. Claudet has presented to the Academy of Sciences of Paris a memoir 

 on his process of extracting gold and silver from burnt coppery pyrites — a pro- 

 cess extensively conducted at Widnes by Mr. J. A. Phillips. The treatment 

 consists essentially in roasting the burnt ore at a low temperature with common 

 salt, lixiviating the product with water acidulated with hydrochloric acid, pre- 

 cipitating the silver by iodide of potassium, and decomposing the iodide of 

 silver by metallic zinc. It is unnecessary, however, to- enter into details of 

 the process, as it was described by Mr. Phillips at the Liverpool meeting of 

 the British Association. We learn from Mr. Claudet that in 1871 not less 

 than 16,300 tons of burnt pyrites were thus treated at Widnes, and yielded 

 333*242 kilogrammes of silver and 3*172 kilogrammes of gold. 



A capital account of tin-smelting, as practised in Banca, appeared in the 

 first part of the new Dutch periodical on East Indian Mining. The descrip- 

 tion is written by Van Diest, and is illustrated by an effective chromo- 

 lithograph representing the Chinese method of tin-smelting as practised at 

 night. 



MINERALOGY. 



Last quarter we had occasion to refer briefly to the discovery of a new lead- 

 bearing mineral called Maxite. A full description of this interesting species 

 has since been published by Dr. Laspeyres.* Herr Max Braun, of the Vieille 

 Montagne Zinc Mines, near Aix-la-Chapelle, having visited the lead mine 

 known as the Mala Calzetta, near the town of Iglesias, in Sardinia, brought 

 home with him certain specimens of the new mineral, which were at first 

 taken for mendipite or chloro-carbonate of lead. It was soon found, however, 

 that no chlorine was present, and a full analysis has since revealed the fol- 

 lowing composition: — Water, 1866; carbonic acid, 8082; sulphuric acid, 

 8*140; protoxide of lead, 81*912. From these figures the following formula 

 may be deduced (using the old atomic weights) : — 



5(PbO.S0 3 ) + g(PbO.C0 2 )-r-Pb0.5HO. 

 This formula corresponds to 31 per cent of sulphate of lead, 49 of carbonate 

 of lead, and 20 of hydrated oxide of lead. Up to the present time we believe 

 that the mineral has not been found in situ, but the few specimens yet known 

 have all been obtained from the dressing-floor at the mine. During the pro- 

 cess of dressing, the crystals have of course been subjected to attrition, and 

 hence the surfaces are much rubbed and rounded, so that no crystalline faces 

 have yet been found sufficiently distinct to admit of measurement. It is 

 inferred, however, from its cleavage and from its optical properties, that 

 maxite belongs to the rhombic system. It presents the form of a colourless or 

 greyish-yellow crystalline substance, with a pearly adamantine lustre on the 

 cleavage planes. Its hardness is almost equal to that of calc-spar, and its 

 specific gravity is 6*874. Optical examination shows that it is a negative 



* Leonhardt und Geinitz's Neues Jahrbuch fur Mineralogie, U.S.W., 1872, Heft 5, p. 508; 

 Journal fur praktische Chemie, 1872, Heft 10, p. 470. 



