Question and Answer Forum

MISCO Refractometer Q&A Forum

Find answers to many common questions concerning applications, operation, calibration, and maintenance of refractometers:

Salinity Testing (3)

What are all the different salt scales used for? I need to measure salinity content but don’t know what scale I need.

Chemically, salts are ionic compounds that result from the neutralization reaction of an acid and a base. There are several varieties of salts containing chlorides, acetates, fluorides, and sulfates. The most common salt is sodium chloride (NaCl) or regular table salt. Although we have a refractometer scale that will measure most common salts, we also have an extensive list of scales for sodium chloride. You may select from scales for measuring sodium chloride concentration in percent by weight, specific gravity, freeze point, parts per thousand (ppt), g/100g, density, percent saturation, and even Baume. The most common units of measure are percent by weight, percent saturation, and freeze point. The scale that is correct for you depend on what unit of measure you are most interested in. Multiple salt scales can be programed into the MISCO Palm Abbe digital refractometer so you can just change between different units of measure as your needs change. MISCO also has scales available for the salinity of seawater.

Full question

We just purchased a MISCO digital salometer for measuring sodium chloride concentration. We have a process that needs to mix DI water with Sodium Chloride (NaCl) to 100% saturation. I am hoping that the meter I have bought is the correct version for this job?

The MISCO Digital Salometer is a refractometer that measures the percent saturation of sodium chloride (NaCl) salt in water. The refractometer will display the percent saturation of sodium chloride from 0 to 100% as well as display the freeze point of the solution in either Fahrenheit or Celsius (model dependent). A digital Salometer overcomes many of the problems associated with traditional analog Salometers. Traditional Salometers are cumbersome to use and time consuming. They are simply a glass or plastic hydrometer with a special scale that displays degrees SAL instead of specific gravity. In use, the traditional Salometer is floated in a graduated cylinder containing salt brine. The reading is taken at the point at which the surface of the fluid crosses the analog scale divisions; the temperature must then be read with a thermometer, followed by a manual temperature correction of the reading.

There is no method for field calibrating the apparatus; it is difficult to resolve the tiny scale divisions; it must be thoroughly cleaned and dried to prevent salt residue from influencing subsequent readings; and it is easily broken. The MISCO Digital Salometer is much easier to use and much more accurate. Simply place a couple of drops of sodium chloride solution on the measuring surface, close the evaporation cover, and press the button to initiate the readings. The percent saturation is displayed nearly instantly on the large LCD display.

Products

Sodium Chloride Salt Brine Refractometer Salometer,  Sodium Chloride Salt Brine , Percent Saturation , Freeze Point in °C

Sodium Chloride Salt Brine Refractometer Salometer,; Sodium Chloride Salt Brine,; Percent Saturation Freeze Point in °F

 

We have a pool with 18% salt (a mixture of NaCl, CaCl2 and MgCl2). Is there a digital device [refractometer] that can measure the % of salt in the water?

I have some concerns about your ability to measure percent salt in a multi-component mixture with a refractometer. You see, refractometers are very good at measuring binary (two-part) mixtures such as sodium chloride and water, where the refractive index value of water is a constant (static or known) and sodium chloride is the variable. However, when there are many different components in a solution, such as sodium chloride (NaCl), calcium chloride (CaCl2), and magnesium chloride (MgCl2), it is difficult to tell what the contribution is that each component makes to the total refractive index.

So, if the refractive index changes, it is impossible to say, with any certainty, which of the component parts has changed. Since a refractometer only measures the total refractive index of a solution and cannot selectively read the refractive index of one particular component. All water soluble fluids look the same to the refractometer. Therefore it will be impossible to get a reading that is meaningful.

The Palm Abbe refractometer does have scales for binary solutions of sodium chloride (NaCl), calcium chloride (CaCl2), and magnesium chloride (MgCl2), but cannot measure a mixture of all three.