STATION 10. Hot Water Rinse The purpose of the hot water rinse is to eliminate the last traces of process chemicals and to raise the temperature of the metal sufficiently to cause flash drying of the parts before unracking. The principles of operation for the hot water rinse are essentially the same as those for the other single-station rinses. It should be noted that nitric acid or electropolishing solution dragged-in to the hot water rinse from Station 9 may be dried on the work and may interfere with the finished quality. Therefore, some care must be taken to ensure that these chemicals are not permitted to reach excessive levels in Station 10. If staining develops, the hot water rinse tank should be dumped and replaced totally or partially with fresh make-up water. The levels of chemical drag-in to the hot water rinse are likely to be too low to be analyzed by wet chemical analysis. For this reason, a simple test for acidity using pH paper is recommended as a control. Some city and ground water supplies contain unusually high levels of hardness minerals or other contaminants, and rinsing with deionized water may be the only way to produce stain-free work. Water purification companies offer small package units utilizing anionic/cationic resin beds in replaceable cartridges which are useful for generating small quantities of de-ionized water. A conductivity instrument is normally used to control deionized water systems.