Reference method for measuring the surface tension of chromium electroplating: chapter 6

6. Procedure for Measuring Surface Tension

• 6.1 The analysis for surface tension of the solutions is to be done at 25°C and at a rate of 20 drops per minute.
• 6.2 As part of the daily solution checks and before analyzing any samples for surface tension, check the drop count of the stalagmometer using distilled water. The stalagmometer must produce 20 ± 1 drops for the 2.5 ml stalagmometer. If the number of drops is outside the 19 - 21 range, then clean the stalagmometer as per section 9. If this does not produce acceptable results, discard the stalagmometer and obtain a new one.
• 6.3 Collect a sample of plating solution from the plating tank as per section 5.
• 6.4 When the temperature of the collected sample is at 25°C, place the flat end of the stalagmometer into the solution. Using the pipette bulb, draw up the solution to above the top set of lines on the stalagmometer. Place your finger on the top end of stalagmometer or hold the bulb in position while transferring the stalagmometer over a waste receptacle. (Wear nitrile gloves at all times). Release your finger or the bulb and drain the solution into the receptacle.
• 6.5 For each sample of solution for surface tension analysis, fill and empty the stalagmometer at least three times as per section 6.4 with that sample before measuring. This ensures that the interior surface of the stalagmometer is thoroughly wetted with the solution.
• 6.6 To measure the surface tension of the solution, fill the stalagmometer with the sample to above the top set of lines on the stalagmometer. If any foam should appear, then remove the foam by squeezing and releasing the pipette bulb so the solution raises and falls in the top portion of the stalagmometer.
• 6.7 Once the foam is removed, allow the solution to fall to the top set of lines and record the point at which a drop is released. This is the initial starting line.
• 6.8 Release the solution and count the number of drops that fall from the stalagmometer as the liquid level falls to the equivalent line of the bottom set of lines on the stalagmometer. If a partial drop is forming at this point, use the drop count up to that point. Do not count the partial drop as one drop.
• 6.9 Determine the density of the solution using one of the methods in section 7.