Liquid hydrometer scales

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 )... 

Close examination of these equations, shows that accurate calibration of the hydrometer with several different liquids allows a precise graduation of the immersed height directly in specific gravity units, or hydrometer scales (e.g., Baum, Twaddell, API, etc.). 

Table 20.1. Hydrometer scales Scale Liquids heavier than water...

Twaddell Hydrometer. This hydrometer, which is used only for liquids heavier than water, has a scale such that when the reading is multiplied by 5 and added to 1000 the resulting number is the specific gravity with reference to water as 1000. To convert specific gravity at 60°/60°F to Twaddell degrees, take the decimal portion of the specific gravity value and multiply it by 200 thus a specific gravity of 1.032 = 0.032 X 200 = 6.4° Tw. See also special table for conversion to density and Baume scale. 

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.

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. 

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. 

By the spindle.—method by the hydrometer is based upon. the fact that a solid will sink in a liquid, whose sp. gr. is greater than its own, until it has displaced a volume of the liquid whose weight is equal to its own and all forms of hydrometers are simply contrivances to measure the volume of liquid which they displace when immersed. The hydrometer most used by physicians is the urinometer (Fig. 4). It should not be chosen too small, as the larger the bulb, and the thinner and longer the stem, the more accurate are its indications. It should be tested by immersion in liquids of known sp. gr., and the error at different points of the scale should be noted on the box. The most convenient method of using the instrument is as follows The. cylinder, which should have a foot and rim, but no pouring lip,. 

Hydrometer hI- dra-mo-t3r (1675) n. An instrument that senses and indicates the density of a liquid in order to measure the specific gravity of a liquid or solution. A simple type consists of a glass tube with a bulb at its bottom, fine lead shot in the bulb, and a graduated scale within the tube. The amount of shot is adjusted before the top of the tube is sealed so that, when the hydrometer is floated in a liquid of density within its calibrated range, the scale reads the density of the liquids at the meniscus. 

This is a hydrometer used for meeisuring density (specific gravity) of industrial liquids which are greater than one. Measures of specific gravity between 1 and 2 are divided into 200 equal parts, and each division is 1 degree. The specific gravity of a solution equals the number of degrees on the Twaddell scale multiplied by 5 and divided by 1,000. The Twaddell is named for its inventor. 

A hydrometer is a float caliberated (with water) to indicate specific gravity (usually on API scale) of a 1 iquid by the extent (depth) to which it submerges into the liquid. Though it permits very rapid measurements, a hydrometer is usually employed only where approximate specific gravity is acceptable. 

Pour the liquid sample under test into the hydrometer jar slowly, so as to avoid air bubbles. Suspend in the sample a thoroughly cleaned and dry thermo-hydrometer (a hydrometer with a thermometer enclosed in its body, Fig. 4.6). When the hydrometer has come to rest, depress it slightly into the liquid and then release. When the hydrometer has again become stationary, note simultaneously the readings on the gravity scale and the thenno-scale of the hydrometer. 

The API gravity is read by observing the freely floating API hydrometer and noting the graduation nearest to the apparent intersection of the horizontal plane surface of the liquid with the vertical scale of the hydrometer, after temperature equilibrium has been reached. The temperature of the sample is read from a separate accurate ASTM thermometer in the sample or from the thermometer which is an integral part of the hydrometer (thermohydrometer). 

Depress the hydrometer about two scale divisions into the liquid, and then release it. The remainder of the stem of the hydrometer, which is above the level of the liquid, must be kept dry since unnecessary liquid on the stem affects the reading obtained. With samples of low viscosity, impart a slight spin to the hydrometer on releasing to assist in bringing it to rest, floating freely away from the walls of the cylinder. Allow sufficient time for the hydrometer to come to rest, and for all air bubbles to come to e surface. This is particularly necessary in the case of more viscous samples. 

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