|
|
|
|
|
|
|
|
|
|
|
|
|
1. Be sure the Hydrometer is clean and dry.
2. Use a smooth clear cylinder or jar that is dry or well rinsed with portion of sample.
3. Sample must be thoroughly mixed before testing, preferably by a stirrer which reaches the bottom of the sample container.
4. Immerse the Hydrometer slowly in liquid to a point below which it naturally sinks (not over 1/8").
5. Do not make reading until the hydrometer and liquid are at rest and free from air bubbles.
6. The temperatures of the hydrometer and liquid tested should be equal.
7. More accurate readings result when the temperature of the sample equals the temperature at which the hydrometer is graduated and approaches that of the surrounding atmosphere. When differences of temperature are unavoidable and vary from the standard, readings can be adjusted by use of correction tables.
8. The surface tension of the liquid can affect the hydrometer indication. The liquid for which a hydrometer is intended must be specified since readings will vary in liquids having the same density but different surface tensions.
9. Hydrometers of equivalent dimensions may be compared with each other even if the liquid used differs in surface tension from the specified liquid, but comparisons of dissimilar instruments, in such a liquid, must be corrected for the effect of surface tension.
10. To avoid errors due to spontaneous changes in surface tension, skimming and formation of surface films of impurities from apparatus, liquid or air, overflow the cylinder immediately before taking the reading.
11. Observe a point below the plane of the liquid surface and then raise the line of vision until this surface, seen as an ellipse, becomes a straight line. The point where this line cuts the hydrometer is the reading of the instrument.12. Errors of parallax when reading thermometer scale can be avoided by aligning the near end of the mercury column, the portions on either side of the stem and that seen through the capillary so they appear to be a straight line. When the eye is in this position the line of sight is normal to the stem.
*Condensed largely from NIST Circular No. 16.
PROPER USE OF THERMOMETERS
Thermometers are one of the most important instruments used in the laboratory. They are a relatively inexpensive means of reliably measuring temperature, provided they are properly used. It is essential that the instruments be used in the manner prescribed if true temperatures are to be ascertained. The following are some terms that should be understood and adhered to when true temperatures are to be obtained.
TOTAL IMMERSION: Thermometer is immersed into medium up to the point of reading.
PARTIAL IMMERSION: Thermometer is immersed up to immersion line or to depth inscribed on the back of the thermometer.
FULL IMMERSION: The complete thermometer is immersed in the medium, including the expansion chamber. (These instruments are read through a window or port in the bath).
IMPORTANT: Thermometers are not always used to indicate true temperatures, particularly where they are used in methods specified by many technical societies such as ASTM. It is most important to position the thermometer exactly as outlined in the method. Any deviation can cause erroneous indications.
PROPER OPERATION OF REFRACTOMETERS
Lift cover plate. Examine prism make sure it is clean. Use pipette to apply a couple of drops of solution to refractometer prism and close plate. Aim the front end in the direction of bright light and focus to your eyesight. Read the corresponding scale where the light and dark boundary line meet,
this is the correct reading. After using wet tissue with distilled water, wipe prism clean.IMPORTANT:
Always set adjustment point on refractometer in the same temperature that solution will be checked. If temperature is varying greatly you should set adjustment point every 30 minutes.Clean prism with distilled water using a wet tissue, wipe prism clean. Never submerge refractometer in any solution!
A refractometer is precision optical instrument. It should be kept in a clean dry environment not close to corrosives. Always handle carefully do not drop or handle roughly, avoid strong shocks.
Do not touch or scratch optical surfaces.Optical performance can not change. If the proper precautions and maintenance is adhered to your refractometer will give you many years of good service.
We have a full line of catalogs that we can send at your request. Please
feel free to
Phone: 501 589-2947...........Fax: 501 589-2285.........Email:
gfgw@hotmail.com
