The conditioning of crucibles and dishes for gravimetric work involves pretreatment to eliminate the dirt and moisture. All containers should be thoroughly leaned with water and then heat-treated under exactly the same conditions as those to which the container will be subjected in the actual determination. If the container is to be used to measure total solids at 103 or 180, it should be conditioned at that temperature. To heat the dish, particularly porcelain ware, at higher temperatures, such as at 550, will drive out more moisture than desired. The dishes should be heated or fired at the desired temperature, cooled in the desiccators and weighed, heated and fired, cooled and weighed, repeatedly, until the container reaches what is known as constant weight. For small dishes with a weight of less than 25 g, this is assumed to be 0.0002 g. for heavier dishes the allowance is greater but never 0.0005 g. with a little experience, the beginner will learn that a preliminary heating or firing of less than 2 h is seldom worthwhile. This is particularly true of new dishes and of old dishes that have not been used for some time. After dishes have been brought to constant weight, they should be kept in a desiccators to avoid collection of dust or adsorption of moisture prior to use.