974 . | . On the Art of Hardening Copper. 
not in the leaft attracted by the magnet, which clearly proved 
that there was *ho iron in the compofition. It exhibited as 
little traces of any other metals, as far as could be judged 
from the afcending vapour, In order to afcertain with what 
nictal the copper had been mixed, twenty-five affayer’s 
pounds of the pureft filings of the above fragment were col- 
_leéted 5. pure nitrous acid was heated in a mate retort, and 
; aiited with difiilled water; and a few of the filings were 
thrown into it: when the firft quantity was diffolved, a few 
. more were added, and this was continued till the whole quan- 
_,tity was put in. | The folution was made to boil for a quarter 
of an hour, and then diluted with a little more diftilled wa- 
ter, in order that a white powder, which remained undiffolv- 
ed, and which I fufpeéted tobe calx of tin, might more rea- 
dily fall to the bottom. After this was done, the bright blue- 
coloured folution, which was found to contain nothing but 
copper, was carefully poured out, and diftilled water was 
: poured | over the white, powder, which was wafhed feveral . 
times in the fame manner, after it had each time remained 
at reft long, enough to allow it to fettle, when it was thrown 
_tpon filtering paper to be farther wafhed. This white pow- 
der, when dry, weighed 5: affayer’s pounds, which gave 215 
pounds of tin calx in the whole hundred. Now, tin calx : 
lofes, by being revived, {, or 25 per cent, of its weight; and ~ 
therefore this 21; pounds of tin calx muft have given 16; | 
pounds of metallic tin in the hundred, which, in an experi- } 
ment made for the purpofe, was found to be nearly the cafe, 
and the regulus obtained was found to be pure. The metallic. 
compound of the before-mentioned dagger blade was made ~ 
therefore of 837 copper, and 16% tin; or, to reckon without i 
fractions, of 84 parts of copper, and 16 parts of tin, ‘a 
By way: of experiment, a compound of this kind, confifting ey 
of pure copper and pure tin, was fufed, and a penknife blade : 
was made of it, which was polifhed and ground in the ufual b 
manner. This blade had all the properties and the external ; 
appearance of the fragment of the dagger. Where'the edge 
was thin, it was eafily turned: it was therefore thought that i 
perhaps, in the dagger before mentioned, the proportion of — 
_ tinwas greater. To ideal this point, another compofition — 
was 
