182 ATTRACTION. 



the marble for introducing upright wires to hold tubes, or Eudiome- 

 ters ; also some oblong mortices, for allowing the ends of tubes, duly 

 recurved, to enter under the edges of vessels to be filled with gas ; 

 and in cases of rapid absorption, to afford a passage for the mercury, 

 into vessels, from which it might otherwise be excluded, in conse- 

 quence of their close contact, with the marble of the reservoir." 



" This reservoir requires nearly six hundred pounds of mercury 

 to fill it completely." 



Water ^cistern for gases. 



Any vessel containing water in sufficient depth to admit of filling 

 the air glasses, will answer in some good degree. There is in the 

 laboratory of Yale College, a pneumatic cistern constructed in 1803, 

 of which an engraving was given in the editions of Henry's Chemis- 

 try published by me, and which has been found very convenient. It 

 is furnished with air cells, which may be understood by an inspec- 

 tion of Dr. Hare's figure below. In mine, there were only the up- 

 per cells here represented under A A, but divided each into two 

 compartments, and nearly beneath them and under water, were hy- 

 drostatic bellows, for throwing in air and gas. From the cells, also, 

 proceeded tubes for the compound blowpipe, but the apparatus in 

 front, representing the arched tubes and the inverted kettle and its 

 treadle, and also the other lower cells under C C, were not in mine. 



Hydro-pneumatic Cistern of Dr. Hare. 



" The figure, here given, is such as would be presented to the eye, 

 were the front of the cistern removed." 



" A A, are two shelves formed by two inverted chests, which are 

 used as cells to contain gas : B is a sliding shelf, over a deep place 

 between the shelves, A A, which is called the well of the cistern." 



