Obfervations on Lead Ore. 879 
evident that, could it be collected, there would be an annual 
faving at each fmelting houfe of above fifty tons, which, 
fuppofing it to be worth four pounds per ton, would 
amount to above two hundred pounds a year. The price 
and quantity of lead fublimate here affumed are probably 
both of them below the truth ; but my end is anfwered in 
giving this hint to perfons engaged in the fmelting 
bufinefs. 
The following experiments, though upon a different 
fubjeft, may not be unacceptable to the lovers of che- 
miftry, as I do not remember to have any where met 
with therm I trouble the Society with a relation of 
them at this time, that I may not hereafter intrude upon, 
their leifure. 
It is commonly known, that the furface of melted 
lead becomes covered with a pellicle of various colours* 
I undertook fome experiments in the courfe of laft win** 
ter, with a view to afcertain the order in which the colours 
fucceeded each other. The lead which lines the boxes 
in which tea is imported from China happening to be at 
hand, fome of it was melted in an iron ladle; but I was 
-much furprized to find that its furface, though it was 
prefently covered with a dufky pellicle, did not exhibit 
any colours. Imagining that the heat was not fuffi- 
ciently ftrong to render the colours vifible, the fire was 
urged till the ladle became red-hot, the calcined pellicle 
upon.; 
