A liquid can be protected from sharp temperature changes caused by air circulation or cold drafts by putting the beaker inside a larger beaker.A liquid product can then be tested, or a test liquid adjusted by addition of end members. Once the temperature of the liquid is taken, the appropriate Sink-Floats can be selected. Changing the temperature of the liquid can be avoided by preparing a table and using several Sink-Floats.Any adjustments, if they must be made, are then minor. The simplest method of temperature control is to standardize tests, when possible, at average room temperature.Density varies inversely with temperature. The operator must know the degree to which a temperature change will affect his result. Temperature changes cause density changes in liquids.Broader temperatures are allowed if three or more floats are used as described. For accurate testing, the temperature of the batch, or at least the test section must be controlled. The sight gauge system must be equipped with screens to prevent the Sink-Float from being washed through. To make a density determination, close valves or shut off mixers, or other agitating systems, to permit the test chamber to come to equilibrium and the Sink-Floats to respond to the density of the liquid. Tanks or pipes equipped with bypasses must provide continuous flow through the by-pass so the sample in the Sink-Float chamber is the same as in the tank or pipe line. If flow cannot be stopped long enough for the Sink-Floats to indicate the density, a by-pass can be arranged. When frequent testing is required, it may justify setting up a vertical sight gauge to contain the Sink-Floats. Semi-Continuous Monitoring – This method is primarily for use with tank and piping systems. A series of Sink-Floats makes adjusting the liquid, by bringing the next heavier Sink-Float into suspension, a simple procedure. The surface can then be skimmed again to remove new floaters. In general, where a series of separations are to be made by adjusting the liquid, it is better to start with a low density. A transparent container such as a lab beaker, cylinder, or battery jar is employed to hold the density liquid, or filled with product for quality control testing. Beaker Method – The most common technique for using Sink-Floats is the “beaker” method.
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