Hardness of Metals and Alloys. 



117 



This Table exhibits a curious fact, viz. the high degree of hard- 

 ness of cast iron as compared with that of all other metals ; and 

 although we found alloys which possessed an extraordinary degree 

 of hardness, still none were equal to cast iron. 



The first series of alloys we shall give is that of copper and 

 zinc. 



Formulae of alloys and per-centages. 



Weight 

 employed. 



Obtained, 

 cast iron 

 = 1000. 



Calculated*, 

 cast iron 

 = 1000. 



ZnCu^jCu 

 Zn Cu'' 



fCu 



IZn 



rcu 



tZn 



ZirCu' 



2"Cu={zn 



ZnCu 



rcu 



tZn 

 CuZn^Cu 



Cu 



CuZn3{Cu 



CuZn^jCu 



CuZn'l^" 

 Y /in 



82-95 1 



1705; 



79-58 1 



20-44; 



74-48 1 



25-52; 



6606 1 



33-94; 



49-32 1 



50-68; 



32-74 1 ; 



67-26; \ 



24-64 1 ; 



75-36 J 1 



19-571 ; 



80-43/ I 



16-30 1 ; 



83-70; \ 



lbs. 

 2050 



2250 



2250 



2270 



2900 



42708 

 468-75 

 468-75 



472-92 

 604-17 



280-83 

 276-82 

 27604 



261-04 

 243-33 



Broke with 1500 lbs. without the 

 point entering. 



Broke with 1500 lbs. with an im- 

 pression 4 millim. deep. 



Entered a little more than the 

 above ; broke with 2000 lbs. 



Entered 2 millims. with 1500 lbs. ; 

 broke with 1700 lbs. 



These results show that all the alloys containing an excess of 

 copper are much harder then the metals composing them, and 

 what is not less interesting, that the increased degree of hardness 

 is due to the zinc, the softer metal of the two which compose 

 these alloys. The quantity of this metal must, however, not 

 exceed 50 per cent, of the alloy, or the alloy becomes so brittle 

 that it breaks as the steel point penetrates. We believe that 

 some of these alloys, with an excess of zinc, and which are not 

 found in commerce owing to their white appearance, deserve the 

 attention of engineers. There is in this series an alloy to which 

 we wish to draw special attention, viz. the alloy Cu Zn composed 

 in 100 parts of — 



Copper 49-32 



Zinc 50-68 



100-00 



* To calculate the hardnes.s of an alloy, we multi])lie(l the per-ccntage 

 quantity of t-ach metal by the respective hardnes.s of that metal, added the 

 two results together, and divided iiy 100. The quotient is the tlieoretieal 

 hardness. 



