eas 
LXXIII. 
AN IMPROVED FORM OF HYDROMETER BY WHICH THE 
SPECIFIC GRAVITY OF LIQUIDS MAY BE ACCURATELY 
DETERMINED AT ANY TEMPERATURE. By rue REV. H. 
O’TOOLE, of Blackrock College, County of Dublin. 
[Read May 18; Received for Publication Junz 28; Published Juny 29, 1898.] 
In numerous manufacturing processes, in commercial transactions, 
and in scientific investigations, an accurate knowledge of the 
specific gravity of the liquids used is a matter of the highest im- 
portance. This knowledge affords, in many cases, the readiest 
means of identifying a given liquid or of detecting in it the pre- 
sence of a foreign substance. More important still it enables us 
in the simplest manner, to estimate the value of alcoholic, sac- 
charine, acid, or other similar solutions: for the density of such 
solutions depends on the amount of alcohol, sugar, acid, &c., which 
they contain. 
It is not therefore to be wondered at that so many methods 
of determining specific gravity should have been proposed. Here, 
it will not be necessary to speak of methods requiring the use of 
sensitive balances or other delicate apparatus. These may be 
useful or necessary for special purposes, but are not of general 
application. In practice some form of hydrometer is almost in- 
variably used. ‘The common hydrometer consists of a long thin 
stem with a weighted bulb at one end; when placed in a liquid it 
floats vertically, and the distance to which it sinks, as,sshown by a 
scale on or inside the stem, indicates the density of the liquid. 
The simplicity ofthis instrument is its principal reeommen- 
dation, but, unfortunately, what is gained in simplicity is lost 
in accuracy. ‘The indications given are only to a certain extent 
approximate, as a little consideration will show. The scale, when 
most carefully made, is obtained by marking on the stem the 
points to which it sinks when immersed in liquids of known den- 
sities, and the intermediate densities are then marked off by some 
method of approximation. As the calibration is made for some 
particular temperature the indications will be incorrect if the 
