ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 609 



(4) That when phosphoretic iron is carburised by the cementation 

 process, the carbon at once causes a separation of phosphide from the 

 solid iron, if it is saturated with phosphide. 



(5) That if highly phosphoretic steel containing much carbon is 

 heated to above the melting point of the phosphide eutectic in contact 

 with some absorbent material, the eutectic simply liquates out of the 

 mass, and is retained in the surrounding substance. 



(6) That when the phosphide eutectic is expelled from the iron by the 

 absorption of carbon in the cementation furnace, a large part of it 

 liquates out of the mass, and falls in the liquid state into the surround- 

 ing charcoal. 



(7) That when saturated solid solutions of phosphide in iron are 

 heated or cooled, they show no thermal critical point at Ar 3 , and the 

 structure is not broken up even when the temperature exceeds 1000° C. ;. 

 therefore there can be no allotropic change from the Beta to the Gamma 

 modification by heating to 1000° C. 



(8) That the proportion of PH 3 given off on dissolving phosphoretic 

 irons free from carbon is approximately inversely in proportion to the 

 amount of phosphorus. 



(9) That when carbon is introduced into irons containing from 0*03 

 to 0*10 p.c. of phosphorus, the proportion of phosphine liberated on 

 solution of the metal steadily decreases with each increment of carbon. 



(10) That the amount of carbon capable of being absorbed in the 

 blast-furnace and crucible by metal containing phosphorus depends 

 upon the proportion of phosphide of iron present. Pure iron free from 

 phosphorus will combine with nearly 5 p.c. of carbon. 



(11) That phosphorus does not appear to cause the separation of 

 graphite from metals high in carbon. 



Practical Problems in the Metallography of Steel. * — Prof. J. O. 

 Osmond points out that in many cases the Microscope is capable of 

 giving warning of the dangerous character of a steel, chemically, and 

 apparently mechanically, safe. 



The micrograph fig. 138, plate XL, shows the transverse section of 

 a rail web reheated to 900° C, and allowed to cool in air; aud this web 

 exhibits the same structure in all the three planes of section presently to 

 be referred to. 



The micrograph fig. 139 shows the structure when the rail was 

 slowly cooled in the re-heating furnace during a period of 50 hours. 



In fig. 138 the pale ferrite has imperfectly segregated in the form of 

 ragged and broken cell-walls imperfectly environing cells of pearlite 

 mixed with unsegregated ferrite. 



In fig. 139 the pale ferrite and dark granular pearlite have perfectly 

 segregated mainly in the form of thick alternating laniinas. The struc- 

 ture last named must be regarded as highly dangerous, because, under 

 vibration the adhesion between the constituents is liable to gradually 

 loosen and finally to be destroyed. Nevertheless, mechanical tests would 

 initially reveal little difference in the ductility of the two pieces of rail. 



The majority of published micrographs exhibit only a single plane 

 of transverse section. Such representation can give only a very partial 



* Nature, lxiii. (1901) pp. 613-1 (3 figs.). 



