ON THE CHEMICAL NATURE Or CAST IRON. 83 



phate containing that salt, the resulting oxide of iron always contained 

 jjlatiuum. The hjalrogen used for the reduction of the iron, as well as for 

 the blowpipe, was prepared by the action of sulphuric acid on zinc, and 

 purified by leading the gas through two wash-bottles, the first containing 

 nitrate of silver and strong nitric acid, and the second caustic soda and 

 acetate of lead, both bottles being half filled with pieces of puniicestone. 

 The oxygen was prepared by heating a mixture of chlorate of potassium 

 with 15-20 per cent, of black oxide of manganese, and washed by leading 

 tkrough caustic soda. All wash-bottle &c. connexions were made of glass, 

 lead, or pure india-rubber tubing. 



The fusion took place in a large platinum crucible (the contents of which 

 was rather more than half a litre) , enclosed in the usual manner in a clay 

 crucible. The dimensions were such that about a kilogramme and a half 

 of the mixture could be fused at each operation. After fusion the crucible 

 is allowed to cool, it is then boiled out with distilled water, and the accu- 

 mulated product of 6-8 fusions washed by decautation with boiling distilled 

 water. The crystalline oxide settles very quickly, and thus allows of a very 

 rapid and thorough washing. The washing was in every case continued 

 several times after the wash-waters ceased to give any turbidity Avith 

 barium nitrate*. The reduction of the oxide thus formed was made in a 

 covered platinum crucible, heated by means of a large Bunsen burner. The 

 hydrogen was introduced by means of a platinum-tube, reaching through 

 the cover to the bottom of the crucible. The gas, purified as described above 

 and dried by chloride of calcium, was always kept slightly in excess, a con- 

 stant stream of gas being obtained by not using a generator, but two large 

 gas-holders joined together, the contents of each being about 600 litres (20 

 cubic feet), two other gas-holders of similar capacity being used for the 

 storage of the oxygen, the one being used to coUect the gas from the retort, 

 the other to contain the gas purified by passing through a strong solution of 

 caustic soda. 



The resulting spongy iroii was pressed into solid buttons by means of a 

 strong coining-press and a diamond mortar, the cylinder of which being 

 about 70 millimetres in height ; the iron, when pressed, forms a cylinder of 

 about 15 millimetres in height, and weighs about 20 grammes. The melt- 

 ing of the compressed iron took place in lime-crucibles, the lime having been 

 previously burnt, slacked, and reburnt, thus forming a fine impalpable pow- 

 der, which was compressed in the crucible mould. 



The best method of fusion was found to be as follows : — The lime-crucible 

 was placed in a slanting position on a piece of lime. One of the oxyhydro- 

 gen-blowpipes, used in the process, played on the outside of the crucible 

 whilst the flame of the other was directed inside. When white-hot, a cylin- 

 der of the compressed iron was thrown into it. It quickly melts, but at the 

 expense of a large quantity of the iron which is oxidized. The amount losfe 

 by oxidation varies between 25 and 50 per cent. In order to obtain a goodi 

 solid button of melted iron, it is necessary to cool it in an atmosphere of 

 hydrogen, which is easily obtained, simply by turning off the oxygen from 

 the blowpipe playing inside the crucible. The button thus obtained weighs 

 about 15 grammes. On analysis, it was found that these buttons were free 

 from phosphorus, silicon, and calcium, but contained a minute trace of sulphur. 



The preparation, on a large scale, of the pure ferrous sulphate and sodiuia 



* It is worthy of mention that the above process to procure pure oxide from the miX' 

 tare of mixed sulphates yields the purest oxide we have as yet obtained. 



g2 



