397

munday. Feb: 16 . 1679

Present ^/mr Colwall/ Dr. Brown, Mr. Aston, mr Hill, ^ /mr Perkins/ Dr King. mr Hooke

We found by tryall that the specifique weight of Siluer was 9 2/3
and that the specifique weight of Lead examined by water was 11 2/3.
And by melting . . . . . . . half an ounce of Siluer & half an ounce
of lead together and weighing the mixture first in air and then
in water. we found the weight of it in the air to be . 439 5/10
and the weight of the same in water to be - 397 4/10
whence we deduced that the specifique grauity thereof was - 10 3/7
and by comparing it wth. what It ought to haue been Supposing
an equall mixture wthout penetration, we found it should haue been 10 2/3
soe that it was found somewt lighter then the medium of their two
specifique gravitys which we supposed to be caught by the wasting of
some part of the Lead into Litharge. soe that it seemes in this com
position the metalls doe not work vpon & penetrate each other
as in some of the other mixtures.

Then wth a hammer & anvill we beat this mixture very flatt to see if
by the strokes of the hammer they could be made to penetrate each
other or to Lye in a closer texture but weighing the peice soe
hammered first in air & then in the water we found the weight
thereof in both cases the same wth the former weight. It was very
malleable and formd of a middle nature as to hardnesse and malle
ablenesse, as it did also as its its colour between Siluer & Lead.

After this we put the same lump into the same crucible and sufferd
it to stand in the fire melted till all the Lead was thrown out of the
Silver into a litharge which remained melted at the top and was
converted into a glasse somewt green yellowish but transparent and which
was very brittle but it was obseruable that soe long as there
remained any Lead wth. the Siluer it kept the same in fusion
though the fire was not very strong but soe soon as it was all
boyled out into Litharge the Siluer grew hard though the lith[arge]
Remained melted into a glasse which we powred out into a cake

Examining the comparatiue weight of this Glasse of Litharge to water
we found it to be the specifique grauity thereof to be 6 3/25 that is
neer 6 1/8. soe that Lead Reduced into glasse hath acquired a
texture twice as ^ /much/ Rarefied as it was whilst a metall.
Examining the Specifique Grauity of a Lump of glasse between white &
green we found it to be to water as 2 1/2 + 1/32. soe that this Glasse of
Lead is almost 3 times as heavy as common Glasse.

Ref: CELL/RS/HF_399  © Centre for Editing Lives and Letters