Description of an Universal Hydrometer . 
after taking its weight in air as before, fix it on the small 
screw of the shank, and see how many grains it will then 
be necessary to add in the top cup, to sink the instrument 
to the mark, with the body on the screw ; which will in 
this case be more than three hundred, on account of its 
buoyancy ; and dividing its weight in air by the differ- 
ence between the weights put in the top cup in each case, 
the quotient will be its specific gravity. 
Thus, if on putting a piece of willow in the upper cup, 
it requires two hundred and fifty-eight grains to sink the 
hydrometer in water, the weight of the wood in air will 
be forty-two grains ; and if on fixing it to the screw be- 
neath, the instrument requires three hundred and twenty- 
eight grains to sink it to the mark in water, (being twenty- 
eight grains more than would be necessary to sink the in- 
strument itself,) we have only to find the difference be- 
tween the weights put into the top cu|, which in this 
case is seventy grains ; and dividing forty-two by seven- 
ty, we have .6 or .000 for the specific gravity of the. 
wood. 
For the man of science, the instrument with its set of 
weights is all that is necessary, and it is packed into a 
very small compass;* but to accommodate it to those 
who are concerned with spirituous liquors, and to brew- 
ers, the inventor attaches a scale, showing the relation 
between specific- gravities and the commercial or techni- 
cal denominations of per cent age with the former, and 
pounds per barrel with the latter. 
It is needless to enumerate the various departments in 
which an attention to the specific gravities of bodies is 
now become of the first consequence, and wherein this in- 
strument might be applied with advantage; and although 
many may be satisfied if they have any arbitrary stan- 
Tlie price of it is five guinea? 
