Year: 1898

page_text: Date of Application, 14th Jan., 1898
Complete Specification Left, 14th Oct., 1898-Accepted. 19th Nov. 1898
I, HUGH O'TOOLE, of Blackrock College, County Dublin, Ireland, Clergyman,
do hereby declare the nature of this invention to be as follows:-
-
This invention has reference to a new or improved hydrometer for the purpose
of testing the specific gravity of liquids in a simple and accurate manner, and
at various temperatures, and whereby the necessity of previously determining
the weight of the instrument is obviated.
The instrument consists of a tube or rod of glass or other suitable material
the base of which is weighted, or provided with a receptacle for carrying a
weighted substance.
At a certain distance upwards from the base is an expanded bulb which serves
the function of floating the instrument vertically when immersed in liquid.
Higher up the tube or rod and at a suitable distance from the expanded bulb
is a second bulb of suitable capacity, and finally at the top of the tube or rod
is provided a dish or funnel for the reception of weights as presently described.
The weight at the base of the tube or rod is so proportioned that the instru-
ment does not sink below a certain standard mark fixed between the two bulbs
when immersed in the lightest liquid for which the instrument is designed.
As thus prepared the instrument is used by placing same in the liquid whose
specific gravity has to be determined and if necessary weighting the top until
the tube or rod sinks to the standard mark above described.
Additional weights are now added until the tube or rod sinks to a second
standard mark between the second bulb and the top of the tube or rod.
These additional weights denote a weight of a volume of the liquid equal the
volume of the instrument comprised between the two standard marks.
The weight of the same volume of water may be similarly determined and
from these data the specific gravity of the liquid may be calculated.
Dated this 13th day of January 1898.
J. K. FAHIE & SON,
Agents for Applicant, 9, Westland Row, Dublin.

page_text: is to be performed, to be particularly described and ascertained in and by the
following statement:―
This invention has reference to a new or improved hydrometer for the purpose
of testing the specific gravity of liquids in a simple and accurate manner, and
at various temperatures, and by means of which the necessity of previously deter-
mining the weight of the instrument is obviated.
The common hydrometer consists of a long thin stem with a weighted bulb
at one end; which when placed in a liquid floats vertically, and the distance to
which it sinks as shown by a scale on the stem, indicates the density of the
liquid.
The simplicity of this instrument is its principal recommendation but, unfortu-
nately, 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 densities, 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 liquids are at any other temperature.
"
This is a defect, for, in practice, it is very troublesome to bring liquids to a
given temperature, especially if they are hotter than the standard and have to
be cooled.
Nicholson's hydrometer having no scale may be used at various temperatures
but it labours under the serious defect that its weight which is liable to vary
through use must be accurately known.
Perhaps the most serious, because altogether unavoidable, source of error is
that due to capillarity, or surface tension.
All estimations of density are based on the supposition that the distance to
which the hydrometer sinks is due to its weight alone; but this is not quite
correct.
The reading of the instrument is also affected, and to a very appreciable
extent, by the capillary attraction of the liquid.
As this capillary attraction is generally different for different liquids, it follows
that a hydrometer will necessarily indicate different densities when placed in
liquids having the same density, but differing in capillarity.
From this it is apparent that specific gravities determined by ordinary hydro-
meters must, in the majority of cases, be considered as little better than fair
approximations.
Now my invention is designed to obviate these defects.
There is no arbitrary scale involved, the weight need not be known; the
effect of capillarity is totally eliminated, and it may be used for various tempera-
tures.
The accompanying drawing shews clearly the construction of the instrument.
It consists of a tube or rod of glass, or other suitable material the base of
which is weighted or may be provided with a receptacle A for carrying a
weighted substance.
A certain distance upwards is an expanded bulb B which serves the function
of floating the instrument when immersed in liquid.
Above this is a second bulb C of suitable capacity, and at the top is a dish or
funnel D for the reception of weights as presently described.
The weighted base is so proportioned that the instrument does not sink below
a certain standard point E fixed between the bulb B and C when immersed in
the lightest liquid for which the instrument is designed.
As thus prepared, the instrument is used by placing same in the liquid whose
specific gravity has to be determined and, if necessary, weighting the top until
it sinks to the standard mark just described.

page_text: Additional weights are now added until the instrument sinks to a second
marked point F between the bulb C and the dish D.
These additional weights are evidently, according to the well known law of
Archimedes, the weight of a volume of the liquid equal to the bulb C.
In this way the weights of the same volume-the volume of the bulb-of
any two liquids may be determined with extreme accuracy, and their relative
densities may easily be calculated.
The fact of having two standard points completely eliminates the effect of
surface tension, so fatal to the accuracy of other forms of hydrometer.
My improved hydrometer should prove useful in junior experimental classes;
it is inexpensive; a beginner can obtain with it the most accurate results, and
above all, the accuracy of the result will depend entirely on the worker.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is:
The use and application of a hydrometer consisting of a tube provided with a
weighted base A, two bulbs B and C, a dished top Ď and marked by two stan-
dard points E and F by the aid of which the necessity of a graduated scale is
obviated, also the necessity of having to determine before hand the weight of the
hydrometer; likewise the inaccuracy due to surface tension is eliminated, sub-
stantially as herein specified and illustrated in the accompanying drawing.
Dad this 12th day of October 1898
J. K. FAHIE & SON,
Agents for Applicant, 9, Westland Row, Dublin.