1040 



TURBA 



2060 



2061 



The mixture, in charges of five to ten cwts., is roasted in a reverberatory furnace on 

 a cast-iron bed of the construction shown in. the annexed engraving. The use of the 

 cast-iron bed is attended with considerable economy in the consumption of fuel, and it 



is admirably well adapted for 

 the calcination of the raw ores, 

 for the evolution of the sulphur 

 and arsenic contained in them, 

 but it is especially necessary, 

 instead of fire-brick or tile, to 

 avoid the loss which would ac- 

 crue from the reaction of the 

 soda-ash on the silica of the 

 brick, and the formation of soda 

 sili'^te of tin which would con- 

 seq nently take place. The mix- 

 ture is introduced to the bed 

 through a hole in the crown of 

 the furnace; from a side door 

 it is equally distributed over 

 the bed, and from time to time 

 it is turned over by the furnace- 

 man until the whole mass is of 

 a dull red heat, emitting a slight 

 hissing sound, and in an in- 

 cipient pasty condition. In suc- 

 cessive quantities the charge is 

 then drawn through a hole in 

 the bed of the furnace into the 

 wrinkle or arch beneath, whence 

 itis removed to cisterns, in which 

 it is lixiviated with water, and 

 the tungstate of soda is drawn 

 off in solution. The residuary 

 mass left in the cisterns, the 

 whole of the soluble matter 

 having been washed out, is re- 

 moved to the burning-house 

 floors, and is there dressed over 

 again in the usual manner, the 

 final product of the operations 

 being very nearly pure black 

 oxide of tin. The liquid ob- 

 tained is either evaporated sufficiently for crystallisation when set aside to cool, or is 

 at once dried down to powder. The crystals of tungstate of soda thus obtained are 

 colourless, translucent, of a beautiful pearly lustre, having the form of rhombic prisms 

 or of four-sided laminae. 



It has been proposed to use this substance as a mordant for dyeing purposes, as a 

 source of supply of metallic tungsten for the manufacture of alloys, for the manu- 

 facture of the tungstates of lime, baryta, and of lead to be used as pigments ; and 

 still more recently it has been found to be preferable to any other substance, for 

 rendering iabrics non-inflammable, so as to prevent the terrible accidents constantly 

 occurring from the burning of ladies' dresses. For this purpose a patent was obtained 

 by Messrs. Versmann and Oppenheim. 



For the manufacture of metallic alloys a patent has been obtained by Mr. E. 

 Oxland, as a communication from Messrs. Jacob and Koeller. Itis prepared by simply 

 melting with cast steel, or even with iron only, either metallic tungsten, or preferably, 

 what has been termed the ' native alloy,' of tungsten, in the proportion of two to 

 five per cent. The steel obtained works exceedingly well under the hammer. 

 It is very hard and -fine grained, and for tenacity and density is superior to any 

 other steel made. The ' native alloy,' is obtained by exposing to strong heat in a 

 charcoal-lined crucible a mixture of clean powdered wolfram with fine carbonaceous 

 matter. A black steel-grey metallic spongy mass is obtained resembling metallic 

 tungsten. 



The tungstate of soda is used in dyeing. Metallic tungsten is also used for the 

 manufacture of packfong or Britannia metal, by alloying with copper and tin. 



TUHBA. This is a mere local word used in the want of knowledge of a more 

 precise designation. Turba, in Portuguese and Spanish (like Tourbe in French), is 



