ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 517 



Metallography, etc. 



Iron, Carbon, and Phosphorus.* — J. E. Stead has collected and 

 summarized his more recent work on iron-carbon-phosphorus alloys. 

 The investigations and observations described are of varied character, 

 dealing not only with the equilibrium of the ternary system, but also 

 with numerous practical questions arising from the presence of phos- 

 phorus in commercial iron and steel. The cause, effects, and detection 

 of the unequal distribution of phosphorus in iron and steel are fully 

 considered. The cupric reagent which has been successfully used by 

 the author for indicating phosphorus segregation is made by mixing : — 

 Cupric chloride, 10 grin. ; magnesium chloride, 40 grm. ; hydrochloric 

 acid, 20 c.cm. ; alcohol to make up to 1000 c.cm. 



The salts are dissolved in the least possible quantity of hot water, and 

 the hydrochloric acid and alcohol then added. The polished specimens 

 are covered with a thin layer of the reagent, and must not be immersed 

 in a bath of the solution. After one minute's action, the layer of re- 

 agent is shaken off and a second layer is applied and allowed to act 

 for the same length of time. This is repeated until the desired effect 

 is obtained. The specimen is washed with boiling water and dried off 

 with alcohol. The effect of the reagent is to deposit copper on the 

 purer parts of the steel first, the regions containing more phosphorus 

 remaining bright, but as the action of the reagent continues the copper 

 deposit gradually forms on the less pure parts also. Thus by the pro- 

 gressive etching described much information may be obtained as to the 

 degree and distribution of the phosphorus segregation. The regions 

 richest in phosphorus are always the last to be affected by the reagent. 

 As the action of this and similar copper reagents depends on the re- 

 lative solubility of different parts of the metal in dilute acid, and as 

 other elements present in solid solution affect the solubility in the 

 same way as phosphorus does, unequal distribution of nickel, copper, 

 arsenic, chromium, tin, and antimony, if present in the steel, may be 

 indicated by the reagent, and may possibly lead to an erroneous assump- 

 tion of phosphorus segregation. 



In iron free from carbon the phosphorus tends to be uniformly dis- 

 tributed. As the carbon in the fluid metal increases, the phosphorus 

 becomes more and more concentrated in the portions last to solidify, 

 and in highly carburized irons the whole of the phosphorus is con- 

 centrated in the last-solidifying portions. At the temperature of final 

 solidification of steel, the last-solidifying portions have a high-carbon as 

 well as a high-phosphorus content. In the subsequent cooling, the 

 carbon is driven out of the high-phosphorus regions, and in low- and 

 medium-carbon steel ferrite bands are produced. When such local 

 absence of carbon becomes sufficiently pronounced, the carbonless 

 streaks termed " ghosts " are formed. As sulphur commonly segregates 



* Journ. Iron and Steel Inst., xci. (1915, 1) pp. 140-9S (77 figs.) 



