MODIFIED ty COMPRESSION. 137 
Yikewife, fhewed the entire internal folidity of the mafs. Un- 
fortunately, this fpecimen has fuffered much by the fame de- 
cay to which all of them are fubjec& which have loft any con- 
fiderable weight. The part next the outward furface alone 
remains entire. I have never been able to explain, in a fatis- 
factory manner, this difference of durability ; the laft-men- 
tioned refult having loft more in ass an to its weight than 
this. 
AxsouT the beginning of June,I nigelved from Mr Hwreii ETT 
fome pure carbonate of lime, which he was fo good as to pre- 
pare, witha view to my experiments ; and I have been conftant- 
ly employed with it till within thefe few days. 
My firft experiments with this fubftance were peculiarly un- 
fortunate, and it feemed to be lefs eafily acted upon than any 
fabftance of the kind I had tried. Its extreme purity, no doubt, 
contributed much to this, though another circumftance had 
likewife had fome effet. The powder, owing toa cryftallization 
which had taken place on its precipitation, was very coarfe, 
and little fufceptible of clofe ramming ; the particles, therefore, 
had lefs advantage than whema fine powder is ufed, in acting up- 
on each other, and I did not choofe to run any rifk of contami- 
nation, by reducing the fubftance to a finer powder. Whatever 
be the caufe, it is certain, that in many experiments in which 
the chalk was changed to marble, this ‘fubftance remained ‘in a 
loofe and brittle ftate, though confifting generally of clearand . 
fhining particles. Tat laft, however, fucceeded in obtaining 
fome very good refults with this carbonate. 
--In‘an experiment made with it on the 18th of June, in a 
{trong heat, I ebtained a very firm’ mafs With a Taline fracture, 
moulded in féveral places on the platina, which was now ufed 
in the cylindrical form. On the 23d; ina fimilar experiment, 
the barrel failed, and the fubject of experiment was ‘found in 
an entire ftate of froth, proving its former fluidity. 
‘Wor. VI.—P.I. S On 
