THE SEARCH FOR PRIMAL MATTER 



with a pressure of fifteen pounds to the square inch, 

 that its weight will balance the weight of a column 

 of a heavy substance like mercury to a height of 

 about thirty inches, is known to every one. It is 

 easy to imagine that there is not much air left in 

 a tube, say, that will only support such a column 

 a thousandth of an inch high. Professor Crookes 

 made such improvements in the Sprengel air- 

 pump that the measure of the vacuum he could 

 obtain was represented by a little column only a 

 few hundred-thousandths of an inch high. He 

 could exhaust a bulb so far that it contained less 

 than a millionth part of its original quantity of air, 

 or, for that matter, of oxygen or hydrogen, or any 

 other kind of gas with which it might have been 

 filled to start with. 



This was, and remains to this day, the highest 

 possible vacuum that can be got with an air-pump. 

 Still, measured by the delicate work that is done 

 nowadays in the laboratory, there was yet a com- 

 paratively large quantity of air, or gas, left. Pro- 

 fessor Crookes conceived the idea of making little 

 bulbs, shaped like dumb-bells, and sealing up in the 

 one end some substance like phosphorus or sodium, 

 which grabs very eagerly at water vapor and dif- 

 ferent kinds of gases. This absorbing power in- 

 creases very rapidly with heat, so that, by slightly 

 ning the one end of the bulb in which the 

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