Hy-drome-ter.
1. An instrument for determining the relative densities of liquids.
Distilled water is usually referred to as the standard of comparison.
It consists essentially of a bulb or float weighted at bottom so as to float upright, and having an elongated stem graduated to indicate the density of the liquid by the depth to which it sinks therein.
Hydrometers may be divided into two classes; those with which weights are used and those in which they are dispensed with.
Among the former are
Sykes's,
Jones's, and Siemen's, while Tralle's and many others are of the latter description.
In all, a correction must be applied to the observed indication when the temperature is above or below a certain standard (usually 60° Fah.), in order to obtain the true result.
Many instruments are only constructed with reference to liquids heavier than water; such are
saccharometers, salinometers, and
acidimeters, which, though bearing names, specifically indicating the particular kinds of fluids they are designed to test, are embraced in the general class hydrometer; such also are those adapted for fluids lighter than water, as
alcoholometers and
oleometers; all depend on the same principle, but greater delicacy is secured by confining the measuring capacity of the instrument within comparatively narrow limits, allowing it much greater vertical ranges for equal variations in specific gravity, so that extremely small differences become sensible.
The different weights in those of the weighted class are also intended for this purpose.
Hydrometers are made and specially graduated for testing spirits, petroleum, oil, milk, cream, vinegar, lye, lime-water, acid, ether, alcohol, silver solution, dye solutions, salt water, lime, alkali, sirup, ammonia, beer, bark ooze, eider, shellac, glue, wine, must, urine.
See list under meters.
Sykes's hydrometer is that legally employed in the collection of the revenue in
Great Britain.
It has a flat stem graduated into eleven equal parts, which are again subdivided into two.
Eight different weights, numbered respectively 10, 20, 30, 40, 50, 60, 70, 80, are employed in connection with the instrument.
The proper one to be used depends on the strength of the spirit to be tested.
It is placed on the lower projecting stem, sinking the instrument to a depth corresponding or nearly so to some one of the graduations on the upper stem; this is noted, and also the temperature of the liquid, and the corresponding strength per cent of spirit is then found from tables constructed for the purpose.
Jones's hydrometer is a modification of
Sykes's. It has a square stem, differently graduated on each of its four sides, and three weights which, with the unweighted instrument, correspond to the four scales.
Among those in which weights are dispensed with are Beaume's, the centigrade, etc.
Beaumes, is in very general use in
France and on the Continent of
Europe.
Its scale is based upon a solution containing 10 per cent of chloride of sodium (common salt).
The following table shows the specific gravity corresponding to different degrees of Beaume : —
For Liquids heavier than Water.
| Degrees | Specific | Degrees | Specific | Degrees | Specific |
| Beaume. | Gravity. | Beaume. | Gravity. | Beaume. | Gravity. |
| 0 | 1.000 | 26 | 1.206 | 52 | 1.520 |
| 1 | 1.007 | 27 | 1.216 | 53 | 1.535 |
| 2 | 1.013 | 28 | 1.226 | 54 | 1.551 |
| 3 | 1.020 | 29 | 1.236 | 55 | 1.567 |
| 4 | 1.027 | 30 | 1.246 | 56 | 1.583 |
| 5 | 1.034 | 31 | 1.256 | 57 | 1.600 |
| 6 | 1.041 | 32 | 1.267 | 58 | 1.617 |
| 7 | 1.048 | 33 | 1.277 | 59 | 1.634 |
| 8 | 1.056 | 34 | 1.288 | 60 | 1.652 |
| 9 | 1.063 | 35 | 1.299 | 61 | 1.670 |
| 10 | 1.070 | 36 | 1.310 | 62 | 1.689 |
| 11 | 1.078 | 37 | 1.322 | 63 | 1.708 |
| 12 | 1.086 | 38 | 1.333 | 64 | 1.727 |
| 13 | 1.094 | 39 | 1.345 | 65 | 1.747 |
| 14 | 1.101 | 40 | 1.357 | 66 | 1.767 |
| 15 | 1.109 | 41 | 1.369 | 67 | 1.788 |
| 16 | 1.118 | 42 | 1.382 | 68 | 1.809 |
| 17 | 1.126 | 43 | 1.395 | 69 | 1.831 |
| 18 | 1.134 | 44 | 1.407 | 70 | 1.854 |
| 19 | 1.143 | 45 | 1.421 | 71 | 1.877 |
| 20 | 1.152 | 46 | 1.434 | 72 | 1.900 |
| 21 | 1.160 | 47 | 1.448 | 73 | 1.924 |
| 22 | 1.169 | 48 | 1.462 | 74 | 1.949 |
| 23 | 1.178 | 49 | 1.476 | 75 | 1.974 |
| 24 | 1.188 | 50 | 1.490 | 76 | 2.000 |
| 25 | 1.197 | 51 | 1.505 |
For Liquids lighter than Water.
| 10 | 1.000 | 27 | .896 | 44 | .811 |
| 11 | .993 | 28 | .890 | 45 | .807 |
| 12 | .986 | 29 | .885 | 46 | .802 |
| 13 | .980 | 30 | .880 | 47 | .798 |
| 14 | .973 | 31 | .874 | 48 | .794 |
| 15 | .967 | 32 | .869 | 49 | .789 |
| 16 | .960 | 33 | .864 | 50 | .785 |
| 17 | .954 | 34 | .859 | 51 | .781 |
| 18 | .948 | 35 | .854 | 52 | .777 |
| 19 | .942 | 36 | .849 | 53 | .773 |
| 20 | .936 | 37 | .844 | 54 | .768 |
| 21 | .930 | 38 | .839 | 55 | .764 |
| 22 | .924 | 39 | .834 | 56 | .760 |
| 23 | .918 | 40 | .830 | 57 | .757 |
| 24 | .913 | 41 | .825 | 58 | .753 |
| 25 | .907 | 42 | .820 | 59 | .749 |
| 26 | .901 | 43 | .816 | 60 | .745 |
In
Gay Lussac's centigrade hydrometer the specific gravity of a liquid heavier than water is found by subtracting the indication from 100 and dividing 100 by the remainder; if lighter than water, add the indication to 100 and divide 100 by the sum, thus 10° below 0° = 100/90=1.111 specific gravity; 10° above 0° = 100/110=0.909 specific gravity.
The hydrometer of Brix is that legally used in
Prussia; to ascertain the specific gravity the constant number, 400, is divided by 400 + the indication for liquids lighter than water, and by 400-the indication for those heavier than water.
The formula for
Beck's instrument is precisely similar, substituting 170 for 400.
[
1154]
Tralle's and Gendar's are used in the
United States, the former being adopted by government for ascertaining the duty on distilled spirits.
It is graduated from 0°, the indication in water, to 100°, alcohol, 50° being proof spirit.
A correction is required for temperatures above or below 60° F.
The volume of pure spirit is ascertained (1) when above proof by multiplying the indication by 2 and subtracting 100; and (2) when below proof by multiplying the indication by 2 and subtracting the product from 100.
The commercial hydrometer, Gendar's, is graduated to 100° each way from proof.
To ascertain the per cent of pure spirit: when the liquor is above proof, add 100 to the indication and divide the sum by 2; when below proof subtract the indication from 100 and divide the remainder by 2.
Rousseau's hydrometer, designed for ascertaining the specific gravity of very small samples of liquids, has a cup on the upper part of the stem in which a known amount, as one gramme, of the fluid is placed; the degree of submergence of the stem compared with that caused by an equal volume of distilled water gives the density of the fluid.
There are also hydrometers which indicate the density by means of a steelyard, having on one arm a vessel which is
in equilibrio in a tank when empty.
The mark on the other arm of the scale, at which the weight must be placed to maintain the equilibrium when the vessel is filled with liquid, determines its specific gravity.
Twaddel's hydrometer is used in
England for liquids heavier than water.
Its degrees are converted into specific gravities by multiplying them by 5, adding 1,000, and dividing the sum by 1,000.
Thus, —
20° Twaddel = 20 × 5 + 1,000/1,000 = 1.100
The density of liquids may also be determined by means of a series of glass beads of different specific gravities; the heavier sink and the lighter float on the surface, while one that indicates the precise specific gravity, which is marked in thousandths on its surface, remains in equilibrium at any depth in the liquid.
The subject is fully discussed in Kuppfer's “Handbuch der Alkoholometrie,”
Berlin, 1865.
See also Alcoholometer, Acidimeter, areometer, saccharometer, etc. See list under meter; see also unit.
The most familiar hydrometer, to many, is a hen's egg, used by a farmer's wife to test the strength of lye for making soap.
When it floats as large as a quarter-dollar above the liquid the strength is satisfactory.
Others test it by its action on a feather.
Small hollow glass spheres called bubbles are also used in testing spirits, the rate at which they ascend therein being a gage of the gravity of the liquid.
The hydrometer was in all probability invented by
Archimedes, who was killed in the storming of
Syracuse, 212 B. C. His discovery of the mode of ascertaining specific gravity by displacement of liquid is referred to by many writers of
Europe,
Asia, and
Libya.
Seneca, Pliny, and Galen, who flourished during the first and second centuries of our era, and whose writings refer to the methods then in use of ascertaining the specific gravity of solids and fluids, appear unacquainted with the hydrometer, though the instrument is clearly described by Priscian, who died about A. D. 528.
Synesius of Ptolemais wrote to
Hypatia that he wished to use a
hydroscopium, and requests that she would cause one to be constructed for him. He says, “It is a cylindrical tube, the size of a reed or pipe, a line is drawn upon it lengthwise, which is intersected by others, and these point out the weight of water.
At the end of the tube is a cone, the base of which is joined to that of the tube, so that both have but one base.
This part of the instrument is called
baryllion. If it be placed in water it remains in a perpendicular direction, so that one can readily discover by it the weight of the fluid.”
Hypatia was brutally murdered by a mob of Alexandrine monks, instigated by Cyril, A. D. 414.
With the death of
Hypatia expired another period of intellectual research.
Cyril was the president of the council which condemned
Nestorius.
After a dreary interval of several centuries, philosophy again revived in the city of
Alexandria, while the Papacy shrank out of
Asia and
Africa, ejected from the great capitals Antioch, Jerusalem, and
Alexandria; the Nestorians became the tutors of Mesopotamia and Chaldea, and in connection with the Jews founded colleges.
Among these, that of Djondesabour first instituted a system of academical honors which has descended to our time.
This college was patronized by the
Khalif Haroun al Raschid, who forbade any one practicing medicine until after a satisfactory examination at the college of Djondesabour or that of
Bagdad.
The areometer used by the Saracens about A. D. 1000, and for many centuries, was a form of hydrometer.
It is described by Abu-Jafar Al-Khazini, an eminent Saracenic writer of the twelfth century, and is credited to
Pappus, a Greek philosopher, who was contemporary with
Theodosius the
Great, A. D. 379 – 395.
Al-Khazini refers to the original discovery of
Archimedes, upon which the instrument is based, and takes a very pious view of the line of discovery.
See the “Book of the balance of wisdom,” in Vol.
VI. of the “Journal of the American Oriental Society,” New Haven, 1860.
See
supra, pp. 141, 142.
In the sixteenth and seventeenth centuries, the salinometer was used in the salt-works of
Germany, and is referred to as a well-known invention.
Pepys, in his “Diary,” December 10, 1668, refers to
Boyle's hydrometer as “a bubble to try the strength of spirits with.”
2. A current gage; known also as a
tachometer, rheometer, hydrometric pendulum, Woltmann's mill, etc.
