352 PHYSICAL LABORATORY OF GREAT BRITAIN. 



At temperatures between about 900° and 1,100° the carbon exists in 

 the form of carbide of iron dissolved in the iron, at a temperature of 

 890° the iron which can exist in different forms as an allotropic sub 

 stance passes from the y form to the ft form, and in this form can 

 not dissolve more than 0.9 per cent of carbon as carbide. Thus at this 

 temperature a large proportion of the carbon passes out of the solu- 

 tion. At 680° the remainder of the carbide falls out of the solution as 

 lamina. 



Thus the following- temperatures must be noted: 1,380°, melting- 

 point; L,050 . highest point reached by specimen; 890°, 0.6 per cent 

 of carbon deposited; 680°, rest of carbide deposited. 



To turn now to the details of the photo, the center piece is the 

 cemented steel as it comes from the furnace after the usual treatment. 



These slides are sufficient to call attention to the changes which 

 occur in solid iron, changes whose importance is now beginning to be 

 realized. On viewing them it is a natural question to ask how all the 

 other properties of iron are related to its structure; can we by special 

 treatment produce a steel more suited to the shipbuilder, the railway 

 engineer, or the dynamo maker than any he now possesses? 



These marked effects are connected with variations in the condition 

 of the carbon in the iron; can equally or possibly more marked 

 changes be produced by the introduction of some other elements? 

 Guillaume's nickel steel with its small coefficient of expansion appears 

 to have a future for many purposes; can it by some modification be 

 made still more useful to the engineer? 



We owe much to the work of the alloys research committee of the 

 Institution of Mechanical Engineers. Their distinguished chairman 

 takes the view that the work of that committee has only begun and 

 that there is scope for research for a long time to come at the National 

 Physical Laboratory, and the executive committee have accepted this 

 view by naming as one of the first subjects to be investigated the con- 

 nection between the magnetic quality and the physical, chemical, and 

 electrical properties of iron and its alloys with a view specially to 

 the determination of the conditions for low hysteresis and nonaging 

 properties. 



At any rate we may trust that the condition of affairs mentioned by 

 Mr. Hadfield in his evidence before Lord Rayleigh's commission, 

 which led a user of English steel to specify that before the steel could 

 be accepted it must be stamped at the Reichsanstalt, will no longer 

 exist. 



The subject of wind pressure again is one which has occupied the 

 committee's attention to some extent. 



The Board of Trade rules require for bridges and similar structures 

 (1) that a maximum pressure of .">»; pounds per square foot be pro- 

 vided for. (2) that the effective surface on which the wind acts should 



