Bethlehem Paper - The Action of Dilute Acids on Certain Varieties of Fused Suiphide of Iron

Having occasion several years since to make ferrous sulphide, I attempted to do so by fusing a mixture of coal-brasses (FeS2) and dried ferrous sulphate. A very nice-looking sulphide was obtained; but on attempting to use it, I found that it was insoluble in dilute hydrochloric and sulphuric acids. The subject was laid aside at the time, but has since been taken up; and some curious results have been obtained, which I believe are new. I have made the material by all of the following methods and the product seems to be pretty much the same, however obtained : (a) FeS2 heated to fusion. (b) FeS2, and FeSO4 heated to fusion. (c) FeS2, and Fe2O3 heated to fusion. (d) FeS2, and FeCO3, heated to fusion. (e) FeSO4, and S heated to fusion. (f) Fe2O3 and S heated to fusion. Obtained in this way the mass after cooling breaks easily and is very nearly black in color. On the upper surface of the fused cake the color is generally reddish or brownish black. When this is treated with dilute sulphuric or hydrochloric acid, it refuses to dissolve; but if touched with the point of a file or any piece of wrought-iron, solution of the sulphide takes place with the evolution of sulphuretted hydrogen. If the iron is removed the evolution of gas ceases, and only begins again when the iron is again brought into contact with the fused sulphide. The same thing happens if the iron is connected with the sulphide by means of a platinum wire. But in all the samples of fused sulphide I have obtained, if the iron is allowed to remain in contact with the sulphide for a certain time (which varies with different samples of the fused sulphide) and is then removed, solution of the sulphide continues. Zinc, tin, and magnesium have the same effect as iron. In hydrochloric acid aluminium acts more rapidly even than iron. In sulphuric acid it has little if any effect. Copper in HCl, when brought in contact with the fused sulphide, dissolves quietly without evolution of gas. The solution of copper chloride formed becomes,as it flows down over the sulphide, converted into copper sulphide.