One way of identifying a substance without resorting to fiddly chemical methods is to determine its density.

其中一种不用高精度的化学方法验证物质的办法就是确定它的密度。

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One way to identify a substance without resorting to fiddly chemical methods is to determine its density.

要分辨一种物质，可以用密度测量法。而无须借助费事繁琐的化学分析法。

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Or a radioactive substance may be disintegrating at a known rate and we may be required to determine the amount of material present after a given time.

又如，某种放射性物质可能正在以已知的速度进行衰变，需要我们确定在给定的时间后遗留物质的总量。

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Accordingly, by observing how much of a radioactive substance has decayed, scientists are able to determine how old that substance is.

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The FBI has the lead in that investigation, of course, and has said in its statement that they will be conducting further tests to determine what the nature of the substance is.

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"Additional documentation indicates he refused to submit to a chemical analysis to determine alcohol concentration or presence of an impairing substance at the time of the citation, " the company said.

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