Apparent density, test procedures

This test procedure is applicable to foamed materials. Terminology of the test standard includes an apparent core density and an apparent overall density. The first term is applicable to cellular plastics that have their forming skin removed. The second term is applicable to cellular plastics that have their skin intact. According to the ASTM procedure, the term density with respect to foamed plastics shall be interpreted accordingly. 

No single test is sufficient to detect all possible contaminants and hence multiple procedures must be adopted. Organisms that grow rapidly in cell culture medium are readily apparent when contaminated medium is incubated at 37°C for a few days. Such contamination is not a serious problem as the experiment can quickly be terminated and the contaminated culture eliminated. It is the slow-growing contaminant which produces no obvious change in the medium and which exerts no marked cytotoxic effect, which may be overlooked and yet may dramatically interfere with a biochemical investigation, e.g. satellite DNA bands in CsCl density gradient analyses or unusual forms of enzyme may reflect the presence of a contaminant. 

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