CHAPTER XI 

 PRINCIPLES OF CHEMISTRY 



129. Chemical Properties. In previous chapters we 

 have discussed the necessity of a thorough knowledge of the 

 physical characteristics or properties of the various materials 

 used in industry. It is equally important to understand the 

 chemical "make up" of those materials; that is, their exact 

 composition. Iron and steel, for example, are used more or 

 less in every trade. The iron ore contains many other sub- 

 stances, such as carbon, silicon, phosphorus, sulphur, manga- 

 nese, and so on. Experience has taught the steel-maker 

 that it is desirable to have as little phosphorus and sulphur 

 as possible in the raw pig iron from which he makes his steel. 

 The foundry man requires pig iron without much manganese, 

 because this property tends to make the iron hard and 

 difficult to melt. Silicon in pig iron makes the carbon 

 assume a form called graphite carbon. This tends to weaken 

 the iron and steel bars, rails, sheets, etc., which are made 

 from the pig iron, because it forms flakes between the particles 

 of iron. 



What has been said in regard to iron and steel, applies 

 equally to other materials. A knowledge of the principles 

 of chemistry is needed to understand the composition of 

 these materials, and the chemical processes that take place 

 when they are used in manufacture. In determining the 

 chemical properties of a substance it is necessary to take a 

 small amount of the mixture and analyze it (Fig. 66). 



125 



