328 Mr. Jacob Perkins on 
cementation was unaltered, excepting at the surface, where it 
had become a little concave. 
Being satisfied that the piezometer as first constructed, 
would not show all the compression, I determined to make 
one differently modified. The object was to avoid the fric- 
tion occasioned by the collapsing of the leather upon the rod 
under such great pressure. The drawing in Plate XXXII, 
Fig. 3, shows another modification of the piezometer, made 
since I have been in this country. This proves my suspicions 
to have been correct ; since, under the same pressure, it in- 
dicated nearly double the compression shown by the former. 
This instrument is constructed as follows, Fig. 3 being a 
section of it. It is simply a small tube. A, closed at the end, 
B, and water-tight. At the upper end, C, the water is al- 
lowed to enter through a small aperture, E, closed by a very 
sensible valve opening inwards. The tube is flattened at D, 
in order that it may yield to the expansion of the water when 
* 
taken out of the press. 
The experiment with this instrument was made at Mr. 
Kier’s manufactory, in the presence of many scientific gen- 
tlemen. The piezometer being perfectly filled with water 
(the weight of which was accurately known) was put into an 
hydraulic press, and subjected to a pressure of about three 
hundred and twenty six atmospheres. When it was taken out 
and weighed, there was found an increase of water amounting 
to three and a half per cent. This water had been previously 
boiled, and cooled down to a temperature of forty eight de- 
grees, and kept at the same temperature during the experi- 
ment. 
