428 Dr. Pearson's Observations 
sometimes be seen ; as was observed in the preceding experi- 
ment, §4. (e). 
I suspect that the blue flame from copper when first ignited, 
and which ceases on fusion, is produced by the inflammation 
of a little of the copper already combined with oxygen ; for 
some oxides of copper are so combustible, that if a small part 
of a given mass of them be ignited, the ignition will spread 
rapidly throughout the whole mass. Most probably celts were 
originally chopping tools, as we have shown in a former part 
of this paper, and therefore the addition of zinc to the allay of 
copper with tin would answer no useful purpose. 
v. The fifth conclusion relates to the proportion of the copper 
and the tin to each other, in the ancient metals. I endea- 
voured to estimate the proportion of tin, by comparing the 
quantities of oxide of tin obtained from the ancient metals, 
with the quantities of oxide of tin obtained by the same means 
from allays of copper with known proportions of tin. 
It appears from the analysis of the allays of copper by tin, 
that the oxide of tin afforded by the nitric acid solution is in 
the proportion of about 150 parts from every 100 parts of the 
metal tin, § 6. Exper. 1st — 9th. According to this da um the 
proportion of tin in the old metals is in the following propor- 
tions, or nearly so. 
1. The sauce-pan contains of tin a little more than 14 per 
cent. ; that is about one part of tin and six of copper. 
2. The spear-head contains 14 per cent, of tin ; that is, 
somewhat less than one part of tin and six of copper. 
3. The celt, No. 3 ; a little more than 12 per cent, of tin ; 
that is, about one part of tin, and seven and a half parts of 
copper. 
