PRESSURE UPON THE BASE OF VESSELS. 175 



of vessels it is necessary to mark upon the vessels 1, 2, 

 and 3 the height to which they are filled by an equal 

 quantity of water, namely, the quantity which nearly 

 fills the vessel 1. This will generally be found to be 

 about 40 CC , or 40 gr ; assuming, for illustration, that this 

 is the quantity required, the vessels are to be placed 

 successively upon the plate, 40^ of water poured into 

 each, and the position of the surface marked upon the 

 glass by a scratch with a file, or by pasting on it a 

 narrow strip of paper. Marks must also be placed 

 on the vessels 2, 3, and 4 at the same height as the 

 mark on vessel 1. These marks are shown in fig. 120, 

 and they shall represent the height of 4CF of water. 



The prepared plate is now sus- 

 pended from the left-hand arm 

 of the balance by a thread and 

 counterpoised. A small wire 

 hook is attached to the thread, 

 to facilitate the removal and sus- 

 pension. The vessel 1 is then 

 clamped in the fork of the retort- 

 stand, the thread passed through 

 it, hooked to the scale-pan, and the 

 iork carefully adjusted until the 

 rim of the cylinder everywhere 

 touches the plate, and the small 

 brass rod is exactly in the middle 

 jf the cylinder, as shown in fig. 

 126. The plate is now drawn 



!<>wn, so that the lower rim of ti ' 126 <" i -* n ** real sizc ^ 

 lie cylinder may be slightly oiled, and brought again 

 slowly and carefully into proper contact with the cylinder. 



