of the Sliding Rod Measurement in Hydrometry. 269 
Let a mineral be suspended from the outer bucket, and ren- 
dered equiponderant with the counter-weight (W), by moving 
this further from or nearer to the fulcrum, so that the index 
point (1) may be exactly opposite the point of the beam. Place 
under the mineral a vessel of water, and add as much of this 
fluid to the bucket, by means of the chyometer, as will cause 
the immersion of the mineral. The band (B) which is made 
to slip upon the rod, should be so fastened, by means of the 
screw, as to mark the distance which the rod has entered, in 
expelling the water, requisite to sink the mineral. Having 
removed the vessel of water and the mineral, ascertain how 
many times the same quantity of water, which caused the im- 
mersion of the mineral, must be employed to compensate its 
removal. 
Adding to the number thus found, one for the water (pre- 
viously introduced into the bucket, in order to cause the im- 
mersion of the mineral), we have its specific gravity; so far as 
it may be expressed without fractions. When requisite, these 
may be discovered by means of the second bucket, which gives 
fifths for each measure of water; which, if added to the outer 
bucket, would be equivalent to a whole number, By the eye 
the distance is easily so divided, as to give half fifths or tenths. 
Or, the nearest bucket being hung one half nearer the ful- 
crum, the same measures will become tenths in the latter, which 
would be units, if added to the outer bucket. 
Rationale. 
The portion of the rod, marked off by the band, was evi- 
dently found competent, by its introduction into the tube of 
the chyometer, to exclude from the orifice a weight of water, 
adequate to counteract the resistance encountered by the mi- 
neral in sinking in water: consequently, to find the specific 
gravity of the mineral, we have only to find how often this 
weight (of water) will go into the weight of the mineral; or, 
what is the same effect, how often the former must be taken, 
in order to balance the Jatter. Indeed it must, otherwise, be 
sufficiently evident, that the mineral and the water being made 
equal in weight, their specific gravities must be inversely as 
their bulks, which are known by the premises. 
The inner bucket may be dispensed with, and greater frac- 
tional accuracy attained, by means of a sector, graduated into 
100 parts. It is for this purpose that the sliding band, and 
the ferule at the but-end of the tube, are severally furnished 
with the points. The assistance of a sector is especially ap- 
plicable, where fluids are in question, since it is necessary to 
find their differences in thousandths. 
To 
