A method has been lieycloped f.or prepari~lg specimens of I' rubber jn a form suitable for precise m eas' urements of t he density. 1'he rubber 'is outgassed in a vacuum chamber, and while still under vacuum is molded into' a sheet abO u E }16 in. ' (1.6 mm) thick . . Specimens ' weighing between 1 and 2 g each are cut fr om this sheet 'and are, erpployed for the measurement of the de n s~t.Y by the method , of hy<;!rqstatic weighings, The values ol;>tained with, diffCl~ent specimens from the ame sample rarely differ from each other by more thaIl 0,05 perc~nt. Measurem ents are made sooh after molding because sonie rubbers reeoY-er, and develOp roughened surfaces and vacuoles which brin g about a decrease in t)le , appllJ"en,t density.
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Wood et al. (1942) studied this question.