Basic Photography Course

HYDROMETERS

237.223

Figure 9-1.Read tbe lower line of the meniscus when measuring

liquids

thermometer, your eyes should be level with the top of
the liquid column in the capillary tube; otherwise, the

reading may be off as much as 2 or 3 degrees. This error
is due to the refraction of the cylindrical magnifier that
is built into the capillary tube.

Most Navy photographic labs have metal, dial type

of thermometers made of corrosion-resistant steel. They

have a long, thin metal stem, or rod, with a circular dial
indicator at the top. The action of this thermometer is

remarkably fast, and the dial is easy to read.

The accuracy of all lab thermometers should be

checked regularly against one of known accuracy, such
as a Kodak process thermometer.

Another measuring device used in photography is

the hydrometer. A "hydrometer" is used to determine the

specific gravity of a solution. A specific gravity check
is one of the first tests to verify the dilution of a solution.
When the same chemicals are used and when the same

quantity of chemicals and an equal volume of water are
used each time, the resulting liquid is approximately the

same specific gravity each time. This is a characteristic
of that particular solution when all specific gravity
measurements are made at the same temperature.

The specific gravity should stay within an upper and

a lower limit as determined by the manufacturer for each
solution. Variations beyond the upper limit-indicating a
denser or heavier liquid-suggest that more than the
prescribed amount of one or more of the ingredients has
been used, an ingredient foreign to the solution has been
added, or not enough water was added to the solution.
Measurements that fall below standard limits might
indicate that something has been left out, that a foreign
chemical has been substituted, or that more than the
correct amount of water was added.

The silver content of a fixing bath increases as the

bath becomes exhausted. This causes the specific
gravity of the solution to rise. Hence, in addition to
testing the consistency of chemical solutions, specific
gravity tests may be used to check the amount of silver
in the fixing bath. A hydrometer used for this purpose
must be calibrated in grams of silver per liter of solution.

A hydrometer consists of a hollow tube with an

enlarged lower section, or float, topped by a narrow
stem. The lower section is weighted, so the hydrometer
will float in liquids with its stem protruding from the
surface. The stem is graduated with marks that are used
to indicate the density of the liquid in which the
hydrometer floats. When the density of the liquid is high,
it supports the hydrometer more easily, so less of the
stem is submerged. Less dense liquids allow the
hydrometer to sink deeper.

Hydrometers are commonly graduated in terms of

specific gravity. Specific gravity is the ratio of the
density of a substance to the density of distilled water.
However, hydrometers designed for special purposes
have different types of graduated scales. An example is
the hydrometer that is used to check the silver content
of a fixing bath.

Because of the effects of surface tension and

capillary action, a meniscus is formed at the interface
between the solution and the hydrometer stem. The

9-3

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Basic Photography Course

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DOFMaster for Windows On-line Depth of Field Calculator DOFMaster for Mobile Devices On-line Depth of Field Table Hyperfocal Distance Chart Articles FAQ Recommended Books Support Contact Links Home As an Amazon Associate I earn from qualifying purchases.	contents <- previous page next page -> HYDROMETERS 237.223 Figure 9-1.Read tbe lower line of the meniscus when measuring liquids thermometer, your eyes should be level with the top of the liquid column in the capillary tube; otherwise, the reading may be off as much as 2 or 3 degrees. This error is due to the refraction of the cylindrical magnifier that is built into the capillary tube. Most Navy photographic labs have metal, dial type of thermometers made of corrosion-resistant steel. They have a long, thin metal stem, or rod, with a circular dial indicator at the top. The action of this thermometer is remarkably fast, and the dial is easy to read. The accuracy of all lab thermometers should be checked regularly against one of known accuracy, such as a Kodak process thermometer. Another measuring device used in photography is the hydrometer. A "hydrometer" is used to determine the specific gravity of a solution. A specific gravity check is one of the first tests to verify the dilution of a solution. When the same chemicals are used and when the same quantity of chemicals and an equal volume of water are used each time, the resulting liquid is approximately the same specific gravity each time. This is a characteristic of that particular solution when all specific gravity measurements are made at the same temperature. The specific gravity should stay within an upper and a lower limit as determined by the manufacturer for each solution. Variations beyond the upper limit-indicating a denser or heavier liquid-suggest that more than the prescribed amount of one or more of the ingredients has been used, an ingredient foreign to the solution has been added, or not enough water was added to the solution. Measurements that fall below standard limits might indicate that something has been left out, that a foreign chemical has been substituted, or that more than the correct amount of water was added. The silver content of a fixing bath increases as the bath becomes exhausted. This causes the specific gravity of the solution to rise. Hence, in addition to testing the consistency of chemical solutions, specific gravity tests may be used to check the amount of silver in the fixing bath. A hydrometer used for this purpose must be calibrated in grams of silver per liter of solution. A hydrometer consists of a hollow tube with an enlarged lower section, or float, topped by a narrow stem. The lower section is weighted, so the hydrometer will float in liquids with its stem protruding from the surface. The stem is graduated with marks that are used to indicate the density of the liquid in which the hydrometer floats. When the density of the liquid is high, it supports the hydrometer more easily, so less of the stem is submerged. Less dense liquids allow the hydrometer to sink deeper. Hydrometers are commonly graduated in terms of specific gravity. Specific gravity is the ratio of the density of a substance to the density of distilled water. However, hydrometers designed for special purposes have different types of graduated scales. An example is the hydrometer that is used to check the silver content of a fixing bath. Because of the effects of surface tension and capillary action, a meniscus is formed at the interface between the solution and the hydrometer stem. The 9-3 contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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