YSI 9300 Photometer - Manual (Page 136)

PHOTOMETER TEST INSTRUCTIONS
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Silicon, in the form of silica, is one of the earth's most abundant elements.
Silicon is found widely in natural waters as colloidal silica or soluble silicates.
Silica and silicates do not normally cause any problems in water intended for
domestic consumption. However, their presence is undesirable in water used in
a variety of industrial applications. This is because of the tendency of such
water to form a hard scale on equipment. Silica and silicate containing waters
are particularly troublesome in steam generating plant such as high pressure
boilers since silica scale can build up on turbine blades.
Formulations containing silicate are used in industrial water treatment, as it is
necessary to control the silicate within specified levels.
The YSI Silica test provides a simple means of measuring silica and silicate levels in
natural, treated, industrial and cooling waters over the range 0 - 150 mg/l SiO
2
.
Method
Sodium molybdate reacts with silica under acid conditions to produce molybdosilicic
acid. Phosphate reacts in a similar manner. Interference by phosphate is
prevented by introducing a reagent that destroys any molybdo-phosphoric acid
which may form.
The reagents for the method are provided in tablet form and the test is carried
out simply by adding tablets to a sample of water. The intensity of the color
produced in the test is proportional to the silica concentration and is measured
using a YSI Photometer.
Reagents and Equipment
YSI Silica HR No 1 Tablets
YSI Silica HR No 2 Tablets
YSI Silica PR Tablets
YSI 9300 or 9500 Photometer
Round Test Tubes, 10 ml glass (PT 595)
Photometer Method
AUTOMATIC
WAVELENGTH
SELECTION
0 – 150 mg/l SiO
2
PHOT.56.AUTO