IN ROLLED COPPER BY HAMMERING, ETC. 245 



Mean density of rolled copper 8*879 



Mean density of hammered copper 8*855 



Mean density of annealed copper 8"884 " 



The densities of the annealed specimens agree very well, 

 the greatest divergence from the mean being '002, but in 

 both the rolled and hammered pieces the error is much 

 greater. But the plus and minus errors nearly balance 

 each other in these cases, and do not, I think, depend 

 upon the manipulation but upon actual differences in the 

 copper. If it is so, it is interesting to note that the ham- 

 mering and annealing have reduced the pieces to a nearly 

 uniform density. 



I got another piece of sheet copper, thicker than the 

 former one, and said to be of a better quality ; and in fact 

 a very close examination of the surface showed that it was 

 free from the minute perforations and crevices which could 

 be perceived in the first sample experimented upon; I had 

 ten pieces cut from the sheet, weighing each from 420 to 

 520 grains. Their densities were as follows : 



No. I 8-899 No' 6 8-897 



2 8*900 7 ..,,.. 8'90i 



3 8-901 8 8-897 



4 8-898 9 8-899 



5 8-897 10 8-898 



Mean density 8-898 



Being hammered the same as before, the densities found 



were : 



No. I 8-879 J^o- 6 8-882 



2 8-879 7 ^'^79 



3 8-876 8 8-876 



4 8-880 9 8-877 



5 8-877 10 8-875 



Mean density 8-878 



They were then made red hot, and allowed to cool 



slowly; carefully cleaned from adhering oxide, and the 



density of five of the pieces found as follows : 



No. I 8-890 



2 8-906 



5 8-899 



7 8-892 



9 8-893 



Mean density ,.., 8-896 



