Phosphoriscd Portions in Iron and Steel. Bij J. E. Stead. 285 



that it was a eutectic, whereas such structure may be produced, as 

 I have found by actual experiment, by the peculiar way in which 

 the phosphorettic parts of steel are imprisoned in and between the 

 crystallites of iron. 



I have already published the methods of detecting phosphide 

 in pig-irons by the Microscope ; and it only remains for me to 

 describe other methods for differentiating between the portions 

 higher and lower in phosphorus in commercial irons and steels. 



The following are detailed directions for applying the several 

 methods. 



Heat Tinting Methods. 



When polished iron or steel is heated in air the surface becomes 

 coloured by the formation of films of oxide of iron. In proportion 

 as the temperature is raised, or continued at one suitable tempera- 

 ture the tints pass from pale yellow to yellow, brown, purple, blue, 

 and steel grey, and through the same series of tints a second time 

 if the heating is continued, but the tints of the second series are not 

 so intense as those of the first. 



Massive carbide of iron becomes coloured less rapidly than iron 

 and more rapidly than phosphide of iron, whilst iron containing 

 phosphorus in solid solution colours more rapidly than pure iron 

 or iron containing less phosphorus. 



Method 1. — Into an iron crucible or ladle, or other suitable 

 receptacle, is placed about 4 ounces of tinman's solder (2 tin, 

 1 lead). The vessel is placed over a Bunsen burner and the solder 

 melted. Into the metal a Le Chatelier couple, covered with a thin 

 piece of asbestos paper, is inserted. The flame of the burner is 

 adjusted until the temperature of the metal stands at 250° C. 

 The specimens, having been polished, are rubbed with a piece of 

 clean woollen cloth, and are warmed on a hot-plate, or in a boiling 

 water oven, and when still warm they are again rubbed with the 

 cloth. They are then floated on the molten metal. The reason 

 for first gently heating is to prevent condensation of acid water 

 from the waste products of the burning gas. If the precaution is 

 not taken the specimen after heating will be covered with minute 

 coloured dots due to condensed steam. The surfaces of the speci- 

 mens are watched and examined with a strong magnifying glass. 

 They will assume a regular yellow tint, and in a few minutes the 

 phosphorised portions will become brown on a yellow ground, 

 and if the heating is continued they will become coloured blue, 

 whilst the parts not so high in phosphorus will be brown or 

 dark yellow. At this point the specimens are removed and may 

 be examined under the Microscope, whilst still hot. If the tinting 

 is not sufficiently advanced they may be returned to the bath for 

 further heating. 



Examples, pi. V. figs. 3, 4, 6. 



