IRON 1023 



assayed with the adddition of silica alone, but the magnesian spathic ores require lime. 

 Ores of the fifth class require no flux. 



Method of conducting the assay. One hundred grains of the ore finely pulverised 

 and passed through a silk sieve are well mixed with the flux, and the mixture intro- 

 duced into the smooth concavity made in the centre of a crucible that has been lined 

 with charcoal ; the lining of the crucible is effected by partially filling it with coarsely- 

 powdered and slightly-damped charcoal or brasque, which is then rammed into a 

 solid form by the use of a light wooden pestle. The mingled ore and flux must be 

 covered with charcoal. The crucible thus filled is closed with an earthen lid luted 

 on with fire-clay ; and it is then set on its base in the air-furnace. The heat should 

 be very slowly raised, the damper remaining closed during the first half -hour. In 

 this way the water of the damp charcoal exhales slowly, and the deoxidation of the 

 ore is completed before the fusion begins ; if the heat were too high at first the luting 

 would probably split, and moreover, the slag formed would dissolve some oxide of 

 iron, which would be lost to the button, and thus give an erroneous result. After 

 half an hour the damper is gradually opened, and the furnace being filled with fresh 

 coke, the temperature is raised progressively to a white heat, at which pitch it must 

 be maintained for a quarter of an hour ; the damper is then closed, and the furnace is 

 allowed to cool. As soon as the temperature is sufficiently reduced, the crucible is 

 removed and opened over a sheet of brown paper ; the brasque is carefully removed, 

 and the button of cast iron taken out and weighed. If the experiment has been 

 entirely successful the iron will be found at the bottom of the crucible in a small 

 rounded button, and the slag will be entirely free from any adhering metallic globules, 

 and will resemble in appearance green bottle-glass ; should, however, the slag contain 

 small metallic particles, the experiment is not necessarily a failure, as they may 

 generally be removed by washing and the magnet. But if on breaking the crucible, 

 the reduced metal should be found in a partially melted state, and not collected into a 

 distinct mass, it indicates either too low a temperature or an improper selection of 

 fluxes, and the experiment must be repeated. The iron obtained is not chemically 

 pure, but contains carbon, and if the ore is manganiferous, manganese ; the result is 

 therefore somewhat too high, though indicating with sufficient exactness for all manu- 

 facturing purposes the richness of the ore assayed. 



Humid Assay of Iron-ores. The quantitative determination of the various sub- 

 stances that occur in iron-ores, demands on the part of the operator a considerable 

 amount of skill and patience, and can only be profitably undertaken by those who 

 have acquired in the laboratory a thorough acquaintance with analytical operations. 

 As, however, much attention has of late years been bestowed on the composition of 

 iron-ores, and as certain elements, viz. manganese, sulphur, and phosphorus, are 

 frequently present, which very considerably affect their commercial value, we deem 

 it right to give a detailed account of the operations to be performed in order to arrive 

 at an accurate knowledge of the composition of an ore. 



Taking for illustration a specimen of the most complicated composition, the 

 substances besides iron to be looked for, and estimated, are water (hygroscopic and 

 combined}, organic matter, sulphur (as sulphuric acid, and as bisulphide of iron), phos- 

 phoric acid, carbonic acid, silicic acid, oxide of manganese, alumina, lime, and alkalis ; 

 lead, tin, copper, and arsenic, are also occasionally met with ; these metals are sought 

 for when a suspicion of their presence is entertained, by a special operation on a large 

 quantity of ore. 



Too great care cannot be bestowed on the sampling of ores intended for analysis ; 

 to expend so much time and labour on an isolated specimen (unless for a special 

 object) is worse than useless ; the sample operated upon should be selected from a 

 large heap, which should be thoroughly gone over, and several dozen pieces taken 

 from different parts ; these should be coarsely powdered and mixed, and about half 

 a pound taken from the mass should be preserved in a well-corked bottle for exami- 

 tion. 



1. Determination of water (hygroscopic and combined}. About 50 grains of the 

 ore are dried in the water-oven till no further loss of weight is experienced ; the loss 

 indicates the hygroscopic water ; the residue is introduced into a tube of hard glass, 

 to which is adapted a weighed tube containing chloride of calcium ; the powder is 

 then gradually raised to a low red heat ; the combined water is thereby expelled, and 

 its amount determined by the increase in weight of the chloride of calcium tube. 

 Some ores (the hydrated hsematites) contain as much as 12 per cent, of combined water. 



'2. Sulphuric acid and sulphur. From 30 to 50 grains of the ore are digested with 

 hydrochloric acid, filtered and washed. The filtrate, concentrated if necessary by 

 evaporation, is precipitated by great excess of chloride of barium. Every 100 parts 

 of the sulphate of baryta produced indicate 34*37 parts of sulphuric acid. The in- 

 soluble residue on the filter is fused in a gold crucible with nitre and carbonate of 



