Size classification of crystals

Some of the more important procedures associated with the characterization of particulate solids are outlined below. 

The physical and chemical characteristics of a bulk quantity of crystaUine material are determined by means of tests on small samples. These test samples must be truly representative of the bulk quantity otherwise any results obtained will be grossly misleading or completely useless. Inefficient sampling followed by careful analysis in the laboratory constitutes a waste of everyone s time and effort. Sampling, which is a highly speciahzed skill, should be carried out by conscientious, well-trained personnel who are fully aware of the tests that are to be made on the sample, without having any direct interest in the outcome of the analyses. 

The actual technique employed for sampling will depend on the nature of the bulk quantity of material, its location, the properties to be tested, the accuracy 

Bulk samples, which may range up to several hundred kilograms for large tonnage lots, have to be reduced to a smaller laboratory sample which, in turn, will have to be divided into several smaller test samples for subsequent analysis. These operations may be carried out by hand or with the aid of a sample divider. 

A simple sample divider is the riffle which usually takes the form of a box divided into a number of compartments with bottoms sloping about 60 to the horizontal, the slopes of alternate chutes being directed towards opposite sides of the box. Thus, when the bulk sample is poured through the riffle, it is divided 

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