264 METALLURGY. 



ajreed concerning thp uses to which the celts were applied, nor 

 whether they are to ht esteemed liritishor Roman instruments) ; it 

 was covered over with a thick patina. 1 heated it in the fire, in 

 order to get rid of this precious patina, or green rust, and took 

 the specific gravity of it when quite freed from its rust, with great 

 care ; a cubic foot of it would have weighed only 6i90 ounces. It 

 Mas not malleable either when hot or cold. 1 then melted it: 

 when in a state of fusion it emitted a blue flame, an I a thick white 

 smoke, which are esteemed certain marks of zinc. 1 melted it a 

 second time, but there was no appearance of either llame or smoke, 

 the zinc had been all consumed : 1 could not observe any lead in 

 it j a cubic foot of it, after it was gently cooled from its stat* of 

 fusion, weighed 8490 ounces ; and it was now malleable, as cold 

 brass always is: it was composed, I think, of copper, calamine, 

 an.) tin ; and I have hoard that some celts contain a little silver. 

 The Change of texture which it had undergone, by being long bu- 

 ried in the earth, occasioned its comparative levity : this diminu- 

 tion of weight, which decaying brass sustains, is not peculiar to 

 brass ; it probably belongs to iron and other metallic substances 

 subject to decay ; and it certainly belongs to many species of 

 stones. I have in another place observed, that a cubic foot of 

 toadstone has different wights, according as the stone is more or 

 less decayed : that whi^h is most decayed being the lightest. We 

 have a stratum of blueish grey ragstone in Westmoreland, which 

 lies under the limestone; large cobbles of this sort of stone, which 

 are exposed to the air, are decayed to a certain depth from the 

 surface, whilst the inward part seems entire ; a cubic foot of the 

 outward part of one of these stones weighed 2378, when the in. 

 ward part of the same stone weighed 2603 ounces to the cubic foot. 

 This ragstone is very hard, but the same phenomenon may be no. 

 tired in a stone still I aider. The Cambridgeshire black flint 

 weighs 2592 ounces to the cubic foot; the same flint being in part 

 decayed and become externally white, though black within, weigh* 

 ed 2414 ; and when become wholly white, '240J ounces to the cu- 

 bic foot ; the general reason of this seems to be, that the pores of 

 the decayed body are augmented. Mr. Kirwan has well explained 

 the- manner in which nature operates in decomposing stones. 

 " Flints, jaspers, petro-silex, felt spar, granites, lavas, and fer- 

 riigineous stones, have frequently been said to be decomposed by 

 the air, and the observations of Mr. Gieville and Sir W. JIamiU 



