GRA 
'With more life and vigour. See Engrav- 
ing. 
GRAVIMETER, the name given by M. 
Guyton to an instrument for measuring spe- 
cific gravities : he adopts this name rather 
than either areometer or hydrometer, be- 
cause these latter terms are grounded upon 
the supposition that a fluid is always the thing 
weighed ; whereas, with regard to solids, the 
liquid is the known term of comparison to 
which the unknown weight is referred. Guy- 
ton’s gravimeter is executed in glass, and is 
of a cy 1 indric form , being that which requires 
the smallest quantity of fluid, and is on that 
account preferable, except so far as it is 
necessary to deviate for the security of a 
vertical position. It carries two basins, 
one of them superior, at the extremity of a 
thin stem, towards the middle of which the 
fixed point of immersion is marked. The 
other, or lower basin, terminates in a point; 
it contains the balls, and is attached to the 
cylinder by two branches. The moveable 
suspension, by means of a hook, has the 
inconvenience of shortening the lever which 
is to secure the vertical position. The cy- 
linder is three fourths of an inch in diame- 
ter, and 6.85 inches in length. It carries 
in the upper basin an additional constant 
weight of five grammes, or one hundred 
and fifteen grains. These dimensions might 
be increased so as to render it capable of 
receiving a much more considerable weight ; 
but this is unnecessary. M. Guyton has 
added a piece which he calls the plonguer, 
because, in fact, it is placed in the lower 
basin when used, and is consequently en- 
tirely immersed in the fluid. It is a bulb of 
glass loaded with a sufficient quantity of 
mercury, in order that its total weight may 
be equal to the constant additional weight 
added to the weight' of the volume of water 
displaced by this piece. It will be readily 
understood that the weight being deter- 
mined at the same temperature at which 
the instrument was originally adjusted, it 
will sink to the same mark on the stem, 
whether it is loaded with a constant additi- 
onal weight in the upper basin, or whether 
the effect of this weight be produced by 
the additional piece in the lower dish. From 
this explanation there will he no difficulty 
in seeing how this instrument may be 
adapted to every case in practice. It may 
be used, 1 . For solids. The only condition 
will be, that the absolute weight of the body 
to be examined shall be rather less than 
the constant additional weight, which in 
this instrument is about 115 grains, g. For 
GRA 
liquids of less specific gravity than watoK, 
the instrument, without the additional weight 
above-mentioned, weighs about four hun- 
dred and fifty-nine grain's, in the dimensions 
before laid down. It would be easy to li- 
mit its weight to the utmost accuracy. We 
have therefore the range of one-fifth of 
buoyancy, and consequently the means of 
ascertaining all the intermediate densities 
from water to the most highly rectified spi- 
rit of wine, which is known to bear in this 
respect the ratio of eight to ten with regard 
to water. 3. When liquids of greater spe- 
cific gravity than water are to be tried, the 
constant weight being applied below by 
meaus of the additional piece, which weighs 
about one hundred and thirty-eight grains, 
the instrument can receive in the upper 
basin more than four times the usual addi- 
tional weight, without losing the equili- 
brium ofits vertical position. In this state 
it is capable of shewing the specific gravity 
of the most concentrated acids. 4. It pos- 
sesses another property, namely, that it 
may be used as a balance to determine the 
absolute weight of such bodies as do not ex- 
ceed its additional load. 5. Lastly, the 
purity of the water being known, it will in- 
dicate the degrees of rarefaction and con- 
densation in proportion to its own bulk. 
To find the specific gravity of any solid by 
the gravimeter, observe tilts rule ; “ From 
the weight in tiie upper dish, when tiie 
instrument is properly immersed in tiie un- 
known fluid, take tiie weight which is placed 
with the body in the same scale at the like 
adjustment. Tiie remainder is tiie absolute 
weight of the solid. Multiply this by the 
specific gravity of tiie fluid, and reserve the 
product. From the additional weight, when 
the body is placed in tiie lower basin, take 
the weight when it was placed in the upper. 
The remainder will be the loss of weight by 
immersion. Divide the reserved product 
by the loss by immersion, and tiie quotient 
will be the specific gravity of tiie solid with 
regard to distilled water at the standard 
temperature and pressure.” To find the 
specific gravity of a fluid, proceed thus ; 
“ To the weight of the gravimeter add the 
weight required in tiie upper basin to sink 
it in the unknown fluid.” Again, “ To the 
weight of the gravimeter add the weight re- 
quired in the same manner to sink it in dis- 
tilled water. Divide the first sunt by the 
latter, and the quotient wili be the specific 
gravity of the fluid in question.” See Spe- 
cific Gravity, Hydrostatics, and Hy- 
drometer. 
