66 MODERN SCIENCE READER 



in homeopathic doses are by no means negligible. Copper 

 and arsenic, aluminium, oxygen, nitrogen, and cyanides are 

 usually present in minute and negligible quantities. 

 Ordinary steel, by whatever process made, is therefore a 

 wonderfully complex alloy, though often spoken of as 

 though it were an elemental substance. It may contain 

 carbon and manganese from 0.10 to 1.50 per cent. ; silicon 

 from 0.02 to 0.25 per cent., and sulphur and phosphorus 

 from 0.01 to 0.10 per cent., and the other elements named 

 above which are rarely determined. Its complexity is 

 further increased by the fact that iron and carbon may 

 exist in several different physical conditions or combina- 

 tions, while the intramolecular possibilities of the other 

 elements are legion. 



When to this very complex base material other elements 

 such as nickel, chromium, tungsten, and vanadium are 

 added, we begin to look wise and talk about alloy steels. 

 Steels within the limits of analysis just mentioned serve 

 an enormous number of purposes, and steel of a particular 

 analysis adapted for rails, springs, knives, or gun barrels 

 may in a limited sense be called a "special" steel, but such 

 is not the commonly accepted use of the term. 



When we materially exceed the limits just given or add 

 elements not normally contained, such as nickel, vanadium, 

 chromium, tungsten, molybdenum, etc., the product is 

 called an alloy or special steel. Silico-manganese gear 

 steel is an instance of an alloy steel containing no unusual 

 elements but containing some of the ordinary elements in 

 unusual amounts. Its analysis is about as follows : Carbon, 

 0.50 per cent. ; silicon, 2.00 per cent. ; manganese, 0.60 

 per cent. 



In such a case it becomes difficult to decide arbitrarily 

 the percentage at which we pass from a regular to a special 

 steel. Abnormally increasing the ordinary constituents 

 or adding other constituents so changes the properties that 

 new qualities appear and new purposes are served. The 

 effects of such additions are made manifest in various ways 



