472 Description of an Universal Hydrometer 
or solids when their specific gravities are required to be 
taken. 
The instrument is accompanied with an accurate set of 
grain weights. 
The weight of the hydrometer itself is seven hundred 
grains? and on adding three hundred grains in the upper 
cup , and immersing it in distilled water? at the tempera- 
ture of 60 degrees of Fahrenheit’s thermometer? it will 
subside to the middle mark on the stem? and will then 
consequently displace one thousand grains of water. 
It follows? therefore? from this adjustment of the bulk 
of the instrument? that each grain in the upper cup will 
represent one thousandth part of the specific gravity of 
the water? or one unit in specific gravity? if that of water 
he taken to be one thousand ; and one-tenth of a grain 
one-tenth of unit? which is also the value of each of the 
small divisions on the stem ; and accordingly? when the 
hydrometer is immersed in any liquid until it sinks 
to the middle point on the stem? the specific gravity of 
such fluid will be indicated by the sum of the weight 
of the instrument (which is? as before stated? seven 
hundred grains) and the grains added in the upper 
cup. 
Suppose? for example? that? on immersing the instru- 
ment in ether? it requires thirty-four grains in the top cup 
to make it* subside to the middle mark on the stem. The 
specific gravity of such ether will in this case be 
700 + 31 = .734. And on putting the instrument into 
alcohol or wort? if it requires in the former case one hun- 
dred and twenty-five grains? and in the latter three hun- 
dred and fifty-five? the specific gravity of the spirit will be 
.825? and that of the wort 1.055. 
To ascertain the specific gravity of a solid ? we have to 
take any fragment less than three hundred grains; find 
its weight in air ? and its weight in water ? and take 
