M\. HIM I>RAWINO AND DESIGN 



In irhite catt iron the whole of the carl \\\ \. \\\ chemical 



i-iiiation with tin- iron, \\hilein greycoat Wtm the carl.on 

 is principally in the free state, that is, siiuj.l\ mi\ ( ! m.-d 

 .ally with the iron. It is the free carl.on which -jives tin- 

 grey iron its dark appearance. A mixture of th- \\lute and 

 grey van <-ast iron when melted i //..//// cost 



'i. The greater tin- amount of cnrl.on chemically combined 

 with tli.- iron, the whit.-r. harder, and nio,-e l.rittle do- 



me. 



Tin- white cast iron is stronger than the -rev. I nit 

 more brittle it is not so suitable for resist inir suddenly 

 loads. White iron melts at a lower temperature than grey 

 iron. I. ut after melting it does not flow so well, <>r il not so 

 liquid as the grey inn. \Vhit<- iron contracts whih- ^n-y iron 



.mis on solidit'yini,'. The jrey iron, t h-i !': . m;iki-s finer 

 castings than the white. Castings aff-r soliditying contract in 

 cooling alxnit J of an inch per foot. Castings posses 

 \arious degrees of strength and hard- produced l,y 



nii'lting mixtures of various proportions of white and _ 

 cast irons. White cast iron has a higher specific gravity t han 

 grey cast iron. 



Cast iron gives little or no warning IM-I'MIV l.n-ukini;. Th.- 

 thickness of the metal throughout a casting in cast iion 

 should be as uniform as possible, so that it may cool and 

 then-fore contract uniformly throughout ; otherwise some j. 

 may l>e in a state of initial strain after the , l-il. 



and will therefore lc easier to fracture. Re-entrant aisles 

 should ! avoided ; such should ! nnindrd nut with fi. 



The presence of phosphorus in cast iron makes it inoiv 

 fusible, and also more brittle. The presence of sulphur 

 diminishes the strength considerably. 



The grey varieties of cast iron are called fom!i // innu or 

 /;,//./,// pig*, while the white rarietlei an- called /; , 

 orf&rgepiga, from the fact that they are used for coi. 

 into wrought ii 



Amongst iron manufacturers the different varieties of cast 

 iron are designated by the numbers 1, 2, 3, *kc., the lowest 

 number being applied to the greyest variety. 



