

ASSAY 2G5 



China Clay, Kaolin, or Hydrated Silicate of Alumna. When pure il contains 

 about 12 per cent, of water. It can be Deprived of this water by heating the powdered 

 clay to a strong red heat. Fire-clays and shale are sometimes used as substitutes 

 for china clay. 



Lime. Unslaked lime is preferable. It forms fusible compounds with .silica, sili- 

 cates of alumina, &c. 



Litharge, or Protoxide of Lead. It forms fusible compounds with silica, and earthy 

 and metallic oxides, &c. Eed lead, or white lead, or carbonate of lead may also be 

 employed. 



Oxides of Iron. Haematite, or iron-scale, may be used as a flux, for silica, and 

 difficultly fusible silicates, &c. 



Black Flux may bo practically regarded as a mixture of carbonate of potash and 

 charcoal. It is prepared as follows : 1 part of nitre, and from 2 to 3 parts of tartar, 

 by weight, are mixed, and. deflagrated by stirring with a hot iron rod until action 

 ceases, or by projecting portions of the mixture from time to time into a hot crucible. 

 The product is reduced to powder and kept in a closely covered jar, as it is liable to 

 absorb moisture rapidly. . The quantity of carbon in the product varies with the pro- 

 portion and purity of the tartar, or argol, employed. Very convenient substitutes are 

 now used by mixing carbonate of soda with from 5 to 10 per cent, of charcoal powder, 

 or with larger proportions of tartar, starch, or flour. 



White Flux is essentially carbonate of potash. It is prepared in the same way as 

 black flux, by deflagrating a mixture of equal parts by weight of nitre and tartar. 

 The nitric acid of the nitre converts the carbon of the tartaric acid in the so-called 

 bi-tartrate of potash into carbonic acid, which combines with the alkali, and carbonate 

 of potash is formed. 



Refining Flux is a variety of white flux, generally made in a similar manner, with 

 salt intermixed. It is used by copper-assayers for refining impure copper. 



KEDUCING AGENTS. Charcoal Powder. Coke dust, and culm or anthracite powder, 

 are also used for some purposes, as they burn away less rapidly than charcoal powder. 



Tartar. Cream of tartar, known in the crude state as red argol and white argol, 

 and when purified, as bitartrate of potash. Starch and flour form convenient sub- 

 stitutes. 



Cyanide of Potassium. Two varieties arc used, one known as gold cyanide, and the 

 other common, which contains a large amount of carbonate of potash. As cyanide of 

 potassium has little fluxing power, for some purposes the latter variety is preferable, 

 as the carbonate of potash forms fusible compounds with silica, &c. 



Iron. Wrought-iron in the form of iron nails, iron rod, or hoop-iron. 



OXIDISING AGENTS. Atmospheric Air. This is the chief agent which acts in 

 roasting processes, in removing sulphur, as sulphurous acid, &c. 



Nitre, or Nitrate of Potash. It is an anhydrous salt, and acts as a powerful oxidising 

 agent, on account of the large proportion of oxygen which it contains. Nitrate of 

 soda may also be used. 



Litharge. Bed Lead. These are also used for oxidising sulphur,- &c. 



Salt, or Chloride of Sodium. It acts as an oxidising agent upon metallic copper. 

 By some assayers it is used in nearly every dry assay process, to top-up with, or 

 cover the other ingredients. On account of its easy fusibility and comparatively low 

 specific gravity, it floats on the top of the products of fusion, and allays effervescence 

 or ebullition when fused. It also acts as a lubricator to the interior of the crucibles; 

 and enables the particles of matter to run down more freely. However, it can readily 

 be dispensed with, and as in most cases its use injuriously affects the result of the 

 assay methods, it is not advisable to employ it. 



SULPHURISING AGENTS, used for forming metallic sulphides, or regulus. Sulphur. 

 Flowers of sulphur or powdered brimstone may be used. 



Iron Pyrites. For some purposes it should be selected free from copper. 



Sulphide of Iron. Made by heating iron and sulphur together, or by fusing iron 

 pyrites with hoop-iron. 



DESULPHURISING AGENTS, used for the removal of sulphur by forming other sul- 

 phides, or by oxidation into sulphurous acid. Iron. Hoop-iron, thin bar-iron, iron 

 rod, or nails, may be used. 



Cyanide of Potassium. 



Carbonate of Soda, dried, or bicarbonate of soda. 



Litharge or Bed Lead. 



ARSENICISING AGENTS, used for forming metallic arsenides or spciss. Arsenic, 

 metallic. 



Arsenious Acid, in admixture with carbon. 



DEAHSENICISING AGENTS, used for the removal of arsenic as a speiss, or by oxidation. 

 Iron, hoop-iron, &c. 



