[ 596 ] 
Knitted in the above-mention’d Experiments, it might 
probably have been render’d pure by a much larger 
Dofe of Lead than is ufually applied for that Purpofe. 
To my Memoir I might have added, that, at- 
tempting to cleanfe a Parcel of the native ‘Platina 
from the black Sand, wherewith it was mixed, I 
found that a great many of its Grains were attra&cd 
by the Magnet I made ufe of for that Purpofe. 
This Circumftance I took notice of in a Letter to 
Lord Lonjdale two Years ago. I am, 
'Dear Sir , 
Tour mojl obliged humble Servant , 
W. Brownrigg. 
XIII. An Account of a very large human Cal- 
culus, ^Win, Heberden M- 2). F. R. S . 
and Fellow of the Coll, of Phyfic. Loud. 
x fad Dec. 20. f | 'HERE is preferved in the Library 
17 5 °* of Trinity -College in Cambridge , 
a Stone taken £rom a human Bladder, which, for 
its uncommon Size, may deferve the Notice of his. 
Society. It is of an oval Shape, flatted on one Side 
and its Surface is fmooth. The fpecific Gravity 
plainly fhews, that it is of an animal Origin ; for its 
Weight is to that of Water only as 1,75 to 1. 
In order to get a true and well-attcfted Hiftory of 
this curious Stone, the Right Rev. Dr. Claggett> 
late Bifhop of Exeter , was applied to, who was 
Keeper 
