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Two glass stoppers act as valves. The sides are ground to fit the glass tube. |
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The purple glass stopper is partially filled with mercury. |
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"W. F. Rohrbeck New York" |
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. |
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Two glass stoppers act as valves. The sides are ground to fit the glass tube. |
|
The purple glass stopper is partially filled with mercury. |
|
"W. F. Rohrbeck New York" |
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