114 4n ANALYSIS of 
tity of water, amounting to about 100 times their own weight, 
'and perhaps more than 200 times their bulk, with which they 
form a confiftent jelly, almoft perfefly tranfparent. 
Ir may be afked here, what prevents the particles of this 
earth from approaching one another more nearly, and entering 
into a ftate of ftronger cohefion? We may, if we pleafe, imagine 
that they retain round each of them, by chemical attraction, a 
quantity of water, which forms a little {phere or polyhedron,with 
the particle of earth in its centre. Thus, each particle is prevented 
from coming within a fmaller diftance of the other particles 
around it, than the diameter of that fphere ; but let the water 
of thefe {pherules be diminifhed in quantity by evaporation, in 
confequence of heat, or the attraction of the -air, the particles 
of the earth will immediately enter into a ftate of clofer con- 
neétion and ftronger cohefion, of which we have examples in 
the exceflive contraction of the jelly, while it is dried up into 
crufts, and in thofe circles of thin incruftation which were 
formed on the fides of the glafs-veflels, while the waters were 
evaporated to drynefs in the firft experiment, the particles of 
which were fo ftrongly united to one another, and to the fur- 
face of the glafs, that they coft me much trouble and time to 
fcrape them off with a knife. 
Wuen fuch a concretion is once formed of this earth, and 
afterwards receives frequent additions of the fame matter, which, 
infinuating itfelf into the pores of the concretion, is fixed there, 
and encreafes its denfity and folidity, the mafs may in time ac- 
quire a furprifing degree of hardnefs. The petrifaclions of 
Geyzer are undoubtedly formed in this manner, and fome of 
them are fo denfe and hard that they are {carcely diftinguifhable 
from agate or calcedony. 
Arter making thefe obfervations on the nature of the fili- 
ceous earth, the proper method for extracting it from the above 
boiled and neutralized portions of thefe waters. was fufficiently 
obvious. I feparately evaporated them to drynefs with a gentle 
heat 
