Sifting Through Sieved Samples

Situation There are two vendors for a particular bulk chemical who meet all written specifications. The products are equally useful for the intended reaction as far as the chemical parameters are concerned both comply in terms of one physical parameter, the size distribution of the crystals, but on the shop floor the feeling prevails that there is a difference. Because the speed of dissolution might become critical under certain combinations of process variables, the chemical engineers would favor a more finely divided raw material. On the other hand, too many fine particles could also cause problems (dust, static charging). 

Questions Are the materials supplied by the two vendors systematically different How could such a difference be quantified  

As it turns out, one vendor s material contains almost no particles (0.5%) in the 261-564 /xm class (bin 15) this means that the %-weight results accurately represent the situation. The other vendor s material, however, contains a sizable fraction (typically 5%, maximally 9%) in this largest size class this implies that 1-5% invisible material is in the size class 564 /xm. Evidently then, the size distribution curve for this second material is accurate only on 

Proceed as if the data were not distorted and carry in mind that any result so obtained is biased. 

Employ a model that mathematically describes a size distribution of this type, adjust the model parameters for best fit, and estimate the missing fraction above 564 /tm after correcting the observed frequencies, continue with a correct statistical analysis. 

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The sample is wet-sieved through a Tyler 300-mesh phosphor-bronze twilled-wire-cloth sieve which passes material finer than 50 /z. All the clay and the finer portion of the silt are washed through the sieve into a 1-liter sedimentation chamber. The silt remaining with the sands is dry-sifted through another 300-mesh Tyler sieve, added to a series of sand sieves. 

Dried milk and nonfat dry milk. Transfer the sample to a dry, air-tight container with a capacity of ca. twice the volume of the sample and mix by shaking and inverting. Sift the sample through a 0.85 mm mesh sieve if necessary to break up any lumps and return it to the air-tight container. 

As part of the preparation for your experiment described in problem 4 you used a mortar and pestle to grind the sample. You were completely satisfied with the result since the powder appeared fine and homogeneous to your eyes, but when you discussed the process with your thesis advisor, he asked you to sift the powder through a 25 pm sieve. This discussion happened just before you were about to take off across campus since your allotted time on the powder diffractometer starts in 10 minutes. Describe your course of action and explain why ... 

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