Different Scales for Refractometers
The Reichert 10440 refractometer used in the Wildland Fire Chemicals Systems (WFCS) laboratory in Missoula, MT, and at many airtanker bases, has an arbitrary scale, with a range of 0 to 30 units. The arbitrary scale commonly is used to test industrial fluids, such as antifreeze. This scale is available in a limited number of refractometer models offered by only a few manufacturers.
The Brix scale is common in refractometers. This scale measures the grams of sugar in 100 grams of pure sucrose solution. An 18 on the Brix scale represents 18 grams of sucrose in 100 grams of a pure sucrose/water solution.
We evaluated refractometers with both types of scales. A conversion chart provided by Reichert was used to convert retardant values from the arbitrary to the Brix scales. The relationship between the two scales is nearly linear, with the Brix scale reading roughly one unit higher than the arbitrary scale. Table 1 indicates specific refractometer values for a given fire retardant in both arbitrary and Brix units. All printed values released by WFCS are based on the arbitrary scale. It is critical to keep the scale in mind when reading printed material from either WFCS or the retardant companies that describe the recommended refractometer values for a particular retardant (known as refractometer targets).
| Retardant | Arbitrary scale (units) | Brix scale (percent) |
|---|---|---|
| Fire-Trol LCA–R/F | 13 to 15 | 14 to 16.2 |
| Fire-Trol LCG–R/F | 14 to 16 | 15.1 to 17.3 |
| Fire-Trol GTS–R | 15 to 18.25 | 16.2 to 19.7 |
| Fire-Trol 300–F | 15 to 18.25 | 16.2 to 19.7 |
| Phos-Chek HV–R/F | 11 to 13 | 11.9 to 14 |
| Phos-Chek MV–R/F | 11 to 13 | 11.9 to 14 |
| Phos-Chek LV–R | 11 to 13 | 11.9 to 14 |
| Phos-Chek LC–95A | 12.75 to 14.5 | 13.8 to 15.7 |
| Phos-Chek LC–95D | 13.75 to 15.75 | 14.8 to 17 |
| Phos-Chek D75–R/F | 11.25 to 13.25 | 12.2 to 14.3 |
| Phos-Chek 259–R/F | 12.25 to 14.5 | 13.2 to 15.7 |
| Phos-Chek G75–F/W | 10.25 to 12.25 | 11.1 to 13.2 |
