Pig Iron undergoes during its conversion into Wrought Iron. 167 
Stlictum.—There is considerable difficulty in determining with 
precision this element in cast iron, and it was only after several 
fruitless trials of various processes that we adopted the following, 
which gave us very satisfactory and concordant results. 5 grms. 
of the iron were dissolved in aqua regia containing excess of 
nitric acid, the whole was then evaporated to dryness and fused 
in a platinum crucible with three times its weight of a mixture 
of pure carbonate of potash and carbonate of soda. The mass 
obtained was dissolved in water and boiled with aqua regia until 
the whole of the peroxide of iron had entered into solution, and 
then was evaporated a second time to dryness and heated care- 
fully to about 200° C. The mass was then treated with hydro- 
chloric acid and water, and the silica on being gathered on a 
filter, was washed with dilute hydrochloric acid until it was per- 
fectly white, dried and calcined, when its weight gave the amount 
of silicium in the iron analysed. 
Sulphur.—In consequence of the small proportion in which 
this element exists in pig iron and wrought iron, considerable 
difficulty is experienced in ascertaining with accuracy the various 
proportions of sulphur existing in iron, and this difficulty was 
increased by the fact that none of the methods recommended 
gave satisfactory results in our hands. Thus, for example, the 
method which consists in determining the sulphur in the state 
of sulphuretted hydrogen, failed, owing to the difficulty of re- 
moving the last traces of sulphuretted hydrogen held in solution 
in the liquid in which the iron is dissolved, and in which the gas 
is produced. As to the process which consists in dissolving the 
iron in aqua regia and boiling off the greater part of the acid, 
and then adding nitrate of baryta to the solution, it cannot be 
followed with security ; for one of us has shown that sulphate of 
baryta is soluble in acid liquors, especially in those containing 
nitric acid, and often in such quantities as to make a greater 
difference between the analysis of two samples of the same iron, 
than the real difference which exists in two samples of iron from 
different ores. These considerations induced us to modify the 
last-mentioned process in the following way :—5 grammes of the 
sample of iron to be analysed were reduced to fine powder, and 
gradually and slowly added to a strongly oxidizing aqua regia, 
composed of four parts of fuming nitric acid and one part of 
hydrochloric acid. The iron being dissolved, the solution was 
evaporated to the consistence of a thin syrup, and then gradually 
mixed with four times its weight of a mixture of pure carbonate 
of potash and soda, and heated to redness for one hour im a pla- 
tinum crucible. The fused mass was then heated with pure 
boiling water until all the soluble portion was dissolved. This 
liquor was then rendered slightly acid with hydrochloric acid, 
