MENTS IN HYDROMETERS AND SACCHAROMETERS
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by the said Thomas Derham at the
Office of the Commissioners of Patents on the 17th September 1883.
THOMAS DERHAм of Bolton in the County of Lancaster.
MENTS IN HYDROMETERS AND SACCHAROMETERS."
"CERTAIN IMPROVE-
The object of my invention is to construct Hydrometers and Saccharometers
that will effectively and correctly indicate specific gravities of spirits, worts, or
other liquids by means of weights, thus dispensing with the necessity for tables of
reference to shew the specific gravities corresponding to each indication on the stem
of the instrument.
It is well-known that Hydrometers in use, are constructed with stems having a
series of weights which sink the instrument in liquids of increased specific gravity,
which do not correctly answer all the purposes for which they were intended.
Since the spirit Hydrometer measures a very extensive range of specific gravities,.
these cannot all be included with any degree of accuracy upon a single stem; and
to adapt the instrument to its purpose a series of weights are employed which aro
successively used to submerge the instrument as the specific gravity of the liquid
in which it floats increases, and the stem of the instrument entirely emerges.
The instrument is so contrived that with any given liquid and the stem entirely
emerged, the required weight next in succession just sinks the stem to the top of
the scale and takes up the series of gravities where the previous weight ended.
With weights of uniform specific gravities as the densities of the liquids increase, a
shorter length of stem is required to indicate an equal range of gravities; hence
the divisions and sub-divisions of the stem have a different value with each new
weight; and with the spirit Hydrometer hitherto contrived, a table is necessary to
shew the specific gravities corresponding to each indication of the instrument.
In instruments of this description the starting point in every series is at the
upper extremity of the stem, thus indicating a whole series in the length of the
stem downwards.
By my invention the instrument is arranged and calculated to indicate all
gravities from the strongest Alchol, which is about 790 at 70 degrees Fahrenheit,
to pure water 1000. This large interval is divided into twenty-one smaller
intervals of ten units each, every lesser interval corresponding to and indicated by
one length of the stem, with its appropriate weight attached to the instrument.
The instrument without any weight and immersed to the top of the graduated
part of the stem or scale indicates specific gravity 790, the next series commencing
at 800 with the 1 weight, and so on in the same way up to 1000. The weights
are stamped with their values, viz, 800, 810, 820, 830, &c.
The stem or scale is divided into ten divisions corresponding to the ten units of..
each series, and each division into five sub-divisions; the value of a sub-division
being 0002, water being unity.

page_text: In the endeavour to give the length of stem or scale one constant value, if the
length of stem indicating gravities from 790 to 800, be selected as the standard of
comparison, the disparity between the real and the indicated gravity progressively
enlarges to the other extremity of the series, being the most considerable in the
interval from 990 to 1000.
By my invention this disparity is nearly practically abolished by several
contrivances.
In the 1st place it is reduced one-half by selecting the length of stem necessary
to indicate the middle series of gravities, namely, from 880 to 900 to indicate
every series of gravities.
In the 2nd place I also select the middle of the stem or nearly so, as the
point where the real shall always correspond with the indicated gravities: by
these means the disparity between the two which would otherwise be accumulated
at the bottom of the stem, is still further divided and distributed one-half above
and the other half below the middle point of the stem.
To be accurate I must point out that as the densities of the liquids increase, the
divisions and sub-divisions measuring equal intervals diminish, hence the point of
stem selected is that which indicates the middle of each series, but which does not
exactly correspond to the middle of the stem; by attention to this an exactly equal
distribution of the disparity between the indicated and real gravities is obtained.
In spirit Hydrometers as at present used, the weights or poises are generally
composed of gilded brass, for which I substitute a metel of light specific gravity,
such as Aluminum, thereby reducing the disparity between the actual and the
required length of stein for any range of gravities, by rather more than one-half.
I would have it understood that although Aluminum is selected, that I do not
bind myself to employ this metal exclusively, as they can be composed of others,
such as, Brass Gilded, Copper, Vulcanite and so on.
By the employment of my invention the principle of division and distribution,
by which the error is minimised to the vanishing point, I give the proportionate
weights and values for an instrument calculated to many places of decimals, and a
table shewing the correspondence of the indicated to the actual gravities.
P
T

page_text: From this table it will be seen that from 840 to 960 the difference between the
real and the indicated gravities in no case exceeds .0001: that the gravity
corresponding to the middle division of the stem and several of the divisions above
and below the middle are always equally free from discrepancy, even in those
extreme series when the discrepancy is the greatest, namely, from 790 to 800,
and from 990 to 1000: that the difference between the real and the indicated gravity
never exceeds 0003, and this only occurs in the series from 790 to 800 when the
whole of the stem is either entirely submerged or emerged. To reduce this
discrepancy between the actual and the indicated gravities so as never to
exceed .0001, we stamp upon the few weights that will be affected thereby, the
few corrections necessary to make the indicated the same as the real gravity,
thereby making the difference actually inappreciable, being one-fourth less than
what is habitually ignored in existing hydrometers.

page_text: In applying my improvements to the Saccharometer, which are similar to those
in the Hydrometer, with the exception of the weight and bulk of the instrument,
the number of series, and the size of the weights to indicate the several series.
The Saccharometer is arranged and calculated to indicate all gravities from 990
or 10 below pure water to 1100. This interval is divided into eleven smaller
intervals of ten units each, every lesser interval corresponding to and indicated by
one length of the stem, with its appropriate weight attached to the instrument, as
in the case of the Hydrometer.
The Saccharometer without any weight and immersed to the top of the divided
part of the stem indicates specific gravity 990. The next series commencing at 1000
with the 1 weight; 1010 with the 2nd weight: 1020 with the 3rd weight and
so on to the end of the series of 1100.
The weights are made of Aluminum, Gilded Brass, Copper, Vulcanite or other
suitable substances as desired, and stamped with their respective values, viz, 1000:
1010 1020 and so on.
:
In Bates' Saccharometer at present in use, the hollow weights or poises vary in
size and weight according to the gravity required, in the proportion of 1.03 to
1:106: 109; 112:1-15 and so on to the end of the series; thus necessitating
great care in the manipulation of the instrument.
The essential difference being that in my instrument the Specific Gravity of the
weights remain constant, whilst in Bates the Specific Gravity of the weights vary
with every fresh series.
The stem of the Saccharometer is divided into 209 parts, the point of middle
gravity of the series being set so that the upper part is in proportion to the lower
as 105 is to 104.
From this table it will be seen that the indicated corresponds to the real
gravities so accurately that taking water as unity, four places of decimals are given. 4
correctly.
The advantages accruing from my invention are as follows:-
That the specific gravities are indicated by means of the weights or poises and
the stem, thus dispensing with the necessity for tables of reference.
That with each weight or poise the same length of stem is used, consequently. 4
each division and sub-division has an identical or almost identical value.

page_text: That the difference between the actual and the indicated gravities is one-fourth
less than in existing hydrometers.
Another important feature in this invention is that of a more extended series,
with the advantages of the decimal system of notation, the progressions from the
beginning of the series of gravities to the end, being by tens, units, and tentlis
That in the case of the Saccharometer, their is practical correspondence between
the real and the indicated gravities.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Thomas Derham in the Patent Office on the 11th March 1884.
THOMAS DERHAM of Bolton in the County of Lancaster CERTAIN IMPROVE-
MENTS IN HYDROMETERS AND SACCHAROMETERS
The object of my invention is to construct Hydrometers and Saccharometers
that will effectively and correctly indicate specific gravities of spirits, worts or
other liquids by means of weights; thus dispensing with the necessity for tables
of reference to shew the specific gravities corresponding to each indication on the
stem of the instrument.
It is well known that Hydrometers in use, are constructed with stems having a
series of weights which sink the instruments in liquids of increased specific gravity,
which do not correctly answer all the purposes for which they were intended.
Since the spirit Hydrometer measures a very extensive range of specific gravities
these cannot all be included with any degree of accuracy upon a single stem; and
to adapt the instrument to its purpose a series of weights are employed which are
successively used to submerge the instrument as the specific gravity of the liquid
in which it floats increases, and the stem of the instrument entirely emerges.
It will be seen that Hydrometers and Saccharometers made upon the principle
of variable immersion to indicate extensive ranges of specific gravities considerable
difficulties are encountered, for should it be attempted to comprise the whole
interval required (of the Spirit Hydrometer for example from 780 to 1000) upon
one length of stem, if accuracy is to be attained, the stem would be exceedingly
long and inconvenient. To obviate this difficulty and permit of the employment of
a short manageable stem, the device has been adopted of attaching weights to the
bottom of the instrument and immersed in the liquid, which just suffice to submerge
the scale of the instrument, when the whole of the scale has emerged through the
increased gravity of the liquid under observation, and repeating the process with
$

page_text: a larger weight as often as may be required for the entire range which the
instrument is to possess. The chief objection to this plan or arrangement is that
with every successive weight, as ordinarily constructed of heavy metals, the length
of the stem possesses a different value: and this repeated variation in the value of
the stem becomes at length so consid-rable, that, in the spirit Hydrometer at
present in most common use, the first range of gravities is nearly one sixth shorter
than the last, though indicated by the same length of stem.
Several methods have been adopted to compensate or correct this variation in
the length of the stem; as, by making the stem with several faces, each possessing
a different scale, but which from obvious disadvantages, such as, having too many
faces, if accuracy were to be attained with the consequent liability to confusion
and error, or the want of accuracy if the faces were few &°, early fell into disuse:
by calculating a table of specific gravities corresponding to the arbitrary indications
of the instrument, a plan which is plainly inconvenient and unscientific: or lastly
by the method well known as Bates'; which consists in making the weights or
poises hollow and of different dimensions, and then employing test liquids, by
trial and experiment with the poises, so to alter their weight and bulk, by the
introduction of weights into their interior, or by removing a portion of the surface,
or by slightly changing in some other way the shape and bulk of the poises, as to
adjust them to the weights and dimensions required. This plan is only applicable
to bollow poises, and is open to the error inseparable from experimental deter-
mination; whilst the hollow poises are liable to alterations in their shape, the least
alteration of which will vitiate the indications of the instrument.
In order that my improvements in Hydrometers and Saccharometers may be
better understood and readily carried into operation I will now proceed to describe
the same by formulæ, tables and calculations.
Having made a careful analysis of the problem of the Hydrometer and
Saccharometer, I have overcome the several difficulties their construction presents
and determined by calculation the exact weights and dimensions of an instrument
for any range of gravities, which will indicate these gravities by means of the
values of the poises and the divisions of the scale or stem. The materials for the
poises may be roughly divided into two classes; each possessing its respective
advantages which will be manifest in the sequel. In the first class are included
metals, such as, brass, copper, zinc, tin, or steel gilded or nickel-plated, aluminium
and others, having specific gravities varying from about 9 to 2-6, and, in the
second class substances of lower specific gravity, such as ivory, celluloid, vulcanite,
and others.
To make an instrument which will itself indicate specific gravities by means of
equal consecutive series corresponding to the successive poises and indicated by the
same length of stem, it is necessary that the stem should have a constant or nearly
constant value, As I have already remarked, if the length of stem corresponding
to the first range of the instrument be selected to indicate all the succeeding ranges,
when solid metallic poises are employed, it will at length be found considerably
longer than is requisite; and if the usual method be followed of graduating the
stem by fixing one end correctly, the discrepancy for each scale or range gradually
increases to the other end of the stem. By my improvements these objections are
partially removed, which I accomplish by calculating the weights and dimensions
to indicate correctly the middle range of gravities, thus dividing and distributing
the discrepancy evenly on both sides of the middle range, instead of allowing it
to accumulate towards one extremity.
I further calculate the weights and dimensions to indicate correctly the middle
gravity instead of the initial gravity of every range, and thus again divide and
distribute the discrepancy one-haif above and one-half below the middle of the
stem, instead of allowing it to accumulate towards one extremity.
By adopting a sufficient number of ranges to cover any given interval of
gravities, the discrepancy may be minimised to the vanishing point, but, as a large

page_text: number of poises might be considered a disadvantage, the same result of perfect
accuracy is obtained by stamping on each poise a fictor or multiplier of the
divisions of the stem counted from the middle; and the product added to, or
subtracted from the indication of the instrument, according to its position above or
below the middle of the stem, will be the correct gravity. In an instrument
calculated upon the plan to indicate the gravities from 780 to 1000, with ten poises
and eleven ranges of twenty units or degrees of gravity each, and brass gilded
with a specific gravity of 9 as the metal of the weights or poises, the third place
of decimals in the extreme case will be barely affected, and this discrepancy the
correcting factor or multiplier will remove. If twenty poises are employed, the
discrepancy is removed into the fourth place of decimals.
Taking aluminium specific gravity 26 as the metal of the poises, with ten poises
the discrepancy affects only the fourth place, and with twenty poises almost
disappears. This method is applicable to any interval or range of gravities, and
any metal of known gravity may be used for the poises, but, as an example, I will
now show how to calculate the weights and dimensions of an instrument of ten
poises and eleven ranges of gravities, to indicate the above interval, namely, from
780 to 1000, taking as the metal of the poises brass gilded, specific gravity 9. For
convenience of calculation the numbers 780. 800. 900 and so on, are treated as
whole numbers though in the resulting quantities the decimal point is restored to
its appropriate place, taking water as unity.
In calculating the dimensions of an instrument, the bulk of the stem is selected
as the unit of measure, which not only facilitates the calculations, but also, as will
be seen hereafter, exhibits in the clearest manner the fundamental principle
governing the relative bulks of the poises, in one class of instrument.
Let d
b
weight of instrument and poise indicating the middle range of gravities
from 880 to 900.
bulk of instrument, including the lower section of the stem, and of the
poise, indicating the middle gravity 890.
v = amount by which the bulk (b) is increased or diminished for any other
range or series of gravities.
Unity
= the bulk of the stem of which
the upper section and y = the lower section,
Then by the well known law

page_text: Putting G the middle gravity of any series, with brass gilded specific gravity 9
for the metal of the poises, the formula for the specific gravity
indicated, becomes

page_text: of their respective series, and that to obtain the gravities for the two ends of the
stem 505618 must be added, and 494382 subtracted from the total bulks.
In the preceding table a comparison has been made of the gravities indicated by
the instrument, and of the corresponding true gravities. It will be seen that the
greatest discrepancy occurs in the two extreme ranges of gravities indicated by
the instrument; that, it is greatest at the two ends of the stem and gradually
disappears, both as the middle range and the middle gravity of every range are
approached; also that it does not exceed in the extreme ranges one (1) in the
third place of decimals whilst from 840 to 940 it barely amounts to the value of
one subdivision of the stem.
This small remaining difference is corrected by stamping upon the poises or
otherwise indicating, a factor or multiplier of the divisions of the scale, counting
from the middle. Should the product of this factor by the number of the division
contain three figures, the correction applies to the third place of the gravities; if
two figures, to the fourth place; the correcting number being the first on the left
of the product. In the preceding example these correcting factors are 10, 8, 6, 4
and 2 respectively.
To illustrate the method of their employment, suppose that the instrument were
employed without any poise, and that the whole of the stem were immersed, the
correcting factor of this range is 10; and since the division of the scale is the
tenth from the middle, 10 x 10 =100; and the correction is one (1) in the third place,
and so on for every other range with its appropriate factor. It must be further
observed that this correction on the side of the low specific gravities, must be added
to the indicated gravity when above the middle of the stem, and subtracted when
below; whilst on the side of the high specific gravities the operation must be
reversed, and the correction subtracted from the indicated gravity when above the
middle, and added when below.
The length of the middle stem or scale is ascertained or obtained by fixing its
upper and lower extremities in distilled water at 60 degrees Fahrenheit, of which
the specific gravity is 1000. This is readily done by calculating the respective
weights, which must be added to the weight of the instrument and poise for
the middle range (without disturbing or affecting the bulk, and therefore at the
top of the stem) in order to sink the instrument in distilled water to the points on
the stem corresponding to the two extremities of the middle range. To illustrate
and make clear the preceding example,
Let ww be the adjusting or test weights for the top and bottom of the stem
natival than

page_text: -
By this method of proceedure, no artificial test liquids are required in the adjust-
ment of the instrument; for if an instrument of any weight and bulk be selected,
but of such a buoyancy that it floats to the top of the stem in distilled water with
the specified weights attached, namely, the poise for the middle range of gravities,
and the first of the adjusting or test weights, bearing their prescribed proportions
to the weight of the instrument all the other details must of necessity be correct;
for the bulk of the stem is fixed by the substitution of the second for the
first adjusting weight; and the weights of the poises having their prescribed
proportions, their bulks are exactly determined by the specific gravity of the
material of which they are composed,. In practice it will be necessary to first
ascertain that the instrument possesses a sufficient buoyancy to float in the
lightest liquid it has to indicate, and the adjustment is effected in the manner
herein described.
T
I now proceed to describe the modifications, occasioned by the employment of
the second class substances above mentioned in the construction of the poises.
Having already stated that when the poises consist of metals of lower specific
gravity than brass, a closer correspondence "cæteris paribus" (other things being
equal) is obtained between the real and indicated gravities. In order to make this
more manifest as well as to exhibit the reason, I have in the following table
instituted a comparison between brass, aluminium and ivory of the specific
gruvities 9, 26 and 178 respectively, shewing the relative bulks of the poises
and the greatest discrepancy in each case.
An examination of this table discloses that in proportion as the specific gravity
of the poises diminishes, the discrepancy between the real and the indicated
gravities also diminishes; the signification of which fact is, that the respective
lengths of the stem required to indicate the extreme ranges more nearly
approximate to that indicating the central range, that is that the stem possesses
a nearly uni'orm value.-Simultaneously also with this approximation to an
uniform value of stem, as a natural consequence of the reduction of the specific
gravity of the material of the poises, the bulks of the latter increase until the
nea ly regular increment to the total bulk for every new range approximates to
unity, which is also the bulk of the stem the tenth poise of specific gravity 1.78
being nearly ten times the bulk of the middle stem. The inference therefore may
be made, that :-
:
If the total bulk is augmented by the bulk of the stem exactly for every new
range of gravities, the stein will possess a constant value and always indicate equal
intervals.

page_text: Assuming therefore the regular increment to the total bulk for every new range
to equal the bulk of the stem; proceed as follows:-
Let dweight of instrument.
If the specific gravity of the first poise be taken as the specific gravity of all
the poises it will be found that there is a deficiency of weight in all the subsequent
poises, but in adjusting the weights care must be taken not to disturb the relative
bulka. To meet and overcome this difficulty one or other of the following methods
must be adopted.
First by increasing the specific gravity of the poises in the necessary proportions,
and secondly, by adding the deficient weight at the top of the stem, where it
will not be submerged by means of small supplementary and correcting weights

page_text: The specific gravity of the poises can be easily adjusted by combining with the
lighter material of the poise a proper proportion of a heavier metal &; for the
specific gravity of two substances being known, the exact proportions by weight of
each required to compound a given weight of an intermediate specific gravity is
readily calculated; or by modifying the composition of the material of the poises
if vulcanite & be employed.
'
It should here be observed that if the device of supplementary weights be
employed, the specific gravity of the poises need not necessarily be 16; for a
material of any specific gravity may be employed, but the plan is only practicable
within certain limits, because if the specific gravity of the material of the poise
be too high or too low the supplementary weights to be subtracted in the former
and added in the latter case become too considerable, and would injuriously affect
the stability of the instrument which is one of the chief advantages attaching
to the principle of submerged weights. As an alternative to the plan of supple-
mentary weights at the top of the stem, since the whole of any given range is
equally affected, the equivalent of the supplementary weights can be stamped upon
their corresponding poises as a correction.
With materials of low specific gravities another method of calculation will give
similar results, and make the stem correspond to equal or nearly equal intervals of

page_text: gravities and that there may be no uncertainty as to the nature or extent of my
invention, I will give a demonstration of the said method
Using the same symbols as before and also putting v = bulk of any one of the
poises; and V = bulk of the next greater;-= gravity of the material of
the poises and G = initial gravity of any range, then by the construction of the
instrument, when the terminal gravity of one range is the initial gravity of.
the next.
•
The weight of the instrument and lesser poise is in the same proportion to the
bulk of the instrument minus the bulk of the sten, and lesser poise, as
the weight of the instrument and greater poise is to the bulk of the instrument
and greater noise.
..

page_text: By selecting such a number of ranges that Z* shall be the square of the power
of Z corresponding to the middle range, not only will the work be much facilitated,
but the further advantage will be secured of fixing correctly the initial gravity of
the middle range as well as of the two extreme ranges.
The example already selected is a very suitable one, and the powers of Z corre-
sponding to the first, middle and last ranges will be Z Z³ and Z10 respectively:
and G. 780: G₁ = 880: G₁
= = 980.
These values substituted in the pressione conection

page_text: #11807
which is constant for every range.
Having thus stated the nature of my invention and described the manner in
which the same is to be or may be performed, or carried into practical effect, I
would have it understood that I do not confine myself to the precise details or
calculations given as the same may be varied or modified without departing from
the principle of my invention, but what I claim as my invention according to the
material of which the poises are composed, and desire to be secured to me by
Letters Patent is :-
First. The use and adaptation of solid metallic poises, with the method of
calculating the weights and dimensions of the instrument, to indicate the middle
range of gravities, and the middle gravity of every range, correctly, as shewn in
Scheme 1; and thus securing an approximation to the uniform value of the stem,
which approximation can be rendered as close as may be desired by simply
increasing the number of the poises; or by securing the same result of accuracy
with fewer poises when they are composed of heavy metals; with the plan of
stamping upon the poises or otherwise indicating, a correcting factor or multiplier
of the divisions of the stem, by the use of which the gravities indicated on the
stem are simply and readily reduced to the true gravities, substantially as and for
the purposes described.
Second. The construction and use of poises composed of materials of low specific
gravities which alone will permit of the attaininent of an uniform value of the
stein with every successive poise, and the practical adaptation of the methods that
have been described; first, of augmenting the total bulk by the bulk of the stem
exactly with solid poises for every new range as shewn in Scheme 2; second, of
increasing the specific gravity of the successive poises in ascertained and regular
proportions as shewn in Scheme 3; third, of employing supplementary weights,
each connected with its corresponding poise, to be used at the top of the stem as
shewn in Scheme 4; or, as an alternative of stamping upon the poises or otherwise
indicating the equivalent corrections;-fourth, the method of employing materials
of low specific gravities, which give an approximation to regularly equal and
consecutive ranges of gravities, so close as to render the gravities indicated by the

page_text: instrument practically identical with the true gravities, which are obtained by the
methods of calculation illustrated in Schemes I and 5.
Third. The method of adjusting the instrument and the length of the stem,
being effected in distilled water at 60° Fahrenheit without the aid of artificial test
liquids.
Fourth-The application of the various methods herein demonstrated to the
construction of instruments well known as Hydrometers and Saccharometers to
indicate any range of gravities, although the range of gravities from 780 to 1000
has been selected for the purpose of illustration substantially as and for the purpose
described.
In witness whereof I the said Thomas Derham have hereunto set my hand and
seal this fifth day of March in the year of our Lord one thousand eight hundred
and eighty four
Signed, Sealed and delivered by the
said Thomas Derham in the presence
of EDMUND CHADWICK
Agent for the patentee.
30 Arrowsmith Terrace.
Bolton.
THOMAS DERHAM (LS)