Hydrometer calibration

Users of the Baum method found that the scale generally read 66 when llie float was submerged in oil of vitriol. Thus, early manufacturers of hydrometers calibrated the instruments by this method. There were variations in the Baumd scale, however, because of lack of standardization in hydrometer calibration. Consequently, in 1904, the National Bureau of Standards made a careful survey and finally adopted the scales previously given for light and for heavy liquids. 

However, a considerable number of hydrometers calibrated according to the Baume scale were found at an early period to be in error by a consistent amount, and this led to the adoption of the equation ... 

As the density gradient along the evaporator develops, a concomitant increase in boiling temperature also is found (Isselhardt et al., 2007). Raw sap boils at 212 °F, and syrup at 66.5 °Bx boils at 219.3 °F (at standard atmospheric pressure). Most producers use a hydrometer, calibrated in Brix or Baume and corrected for temperature, to determine the finished syrup density. 

Each laboratory at explosives plant should be provided with at least one "precision hydrometer calibrated by the National Bureau of Standards in Washington. As these hydrometers are very expensive, it is advisable to use them only for calibration of other laboratory and plant hydrometers, which are much cheaper. A simple method of calibration, such as used during WWII, at Keystone OrdnWorksis described in Ref 8. In this method the following liquids were used kerosene for calibration of hydrometers, range 0.700 to 0.800 iso-butanol for 0.800 to 0,900 boiled distilled water for 0.900 to 1.000 16% (by weight) soln of H2S04 in w for 1.000 to 1.200 41%... 

With the hydrometer technique, both density and depth of immersion vary with each reading. If the temperature is maintained constant at the hydrometer calibration temperature the density may be read directly from the hydrometer stem otherwise a correction needs to be applied [52]. 

There thus appears to be an error of about 0.1 % in the American tables. Jaulmes and Maiignan (1953) have calculated the corrections to be applied when a hydrometer calibrated at 15° C. (59° F.) is used at 20° 0. (68 F.). 

Because of their widespread use for simple process control, hydrometers are frequently calibrated, not in specific gravity, but in some units related to it, which bear (or bore at one time) some relationship to the concentration being so measured. 

The API gravity of water is 10°. A light crude oil would have an API gravity of 40°, while a heavy crude would have an API gravity of less than 20°. In the field, the API gravity is readily measured using a calibrated hydrometer. 

Fig. 3.7. Hydrometer (left) with large weighted bulb and calibrated scale. Pycnometer (right) is filled with fluid and when thermometer is inserted the liquid overflows into the small bulb.

Hydrometers are calibrated in density, specific gravity, and several arbitrary units such as degrees Baume (°Be), degrees American Petroleum Institute (°API), or °Brix. These units are used for specialized purposes in various industries. The relationship between the specific gravity (sp. gr.) of a liquid with a density less than water and these specialized units is given by the following equations ... 

Record the calibration temperature of the hydrometer that is found on the body. 

Baume hydrometer scale phys chem A calibration scale for liquids that is reducible to specific gravity by the following formulas for liquids heavier than water, specific gravity = H5 a- — n) at 60°F for liquids lighter than water, specific gravity = 140 a- (130 + n) at 60°F n is the reading on the Baume scale, in degrees Baume Baume is abbreviated Be. bo ma hT dram-ad-ar, skal )... 

Test Methods and Procedures 4.3.1 Ethyl Alcohol Content. Determine specific gravity at 15.6/l5.6uC (60/60°F) by means of a calibrated hydrometer, pycnometer or other... 

As densities vary with temperature, and as hydrometers are calibrated to be accurate at different temperatures, the fermenting solution should be warmed or cooled to near the calibration temperature for the particular hydrometer used for precise determinations, the actual temperature should be measured and the measured density should be corrected. 

A hydrometer is a very simple device used to measure the density of liquids such as urine or milk. A typical hydrometer has a weighted end to keep it upright in the liquid of interest. These devices are also usually calibrated. When placed in a liquid, a hydrometer will sink until it displaces an amount of fluid exactly equal to its weight. If the fluid is dense, it will displace only a small amount of fluid, and thus not sink very deep. If the density of the fluid is not very high, the hydrometer will sink deeper. The user simply reads the liquid density from the calibrated scale in the neck of the hydrometer. Two examples are shown in Figure 5.5. The fluid on the left has a greater density than the fluid on the right. 

The specific gravity of your urine samples will be measured with the aid of a hydrometer (urinometer see Fig. 52.1). Place the bulb in a cylinder. Add sufficient urine to the cylinder to make the bulb float. Read the specific gravity of the sample from the stem of the hydrometer where the meniscus of the urine intersects the calibration lines. Be sure the hydrometer is freely floating and does not touch the walls of the cylinder. In order to use as little urine as possible, the instructor may read the normal and two pathological urine samples for the whole class. If so, you will measure the specific gravity of your own urine sample only. 

For accurate work it is necessary to take into account certain correction factors, namely the meniscus correction and the change in suspended material, it is necessary to make readings at the top of the meniscus. Hence, there must be added to the latter a small quantity to correct for the procedure. In the case of water suspensions this correction is about 0.0003, and this figure is generally used. 

The second correction involves a correction for temperature. If poc denotes the density of water at calibration temperature, Tc (20 deg C as a rule), and h is the hydrometer reading at any temperature T% then it may be shown that the value of [Pg.83]

The weight of solids per unit-volume of suspension, W, entails no difficulty in its determination pycnometric methods, or simply by weighing a given "amount and displacement in a calibrated graduate. 

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