157 
For this purpose the scalar value of the smallest weight was first directly 
determined and then that of the difference between two successive 
ones. Every weight, the largest weighs about 3 mer., the smallest 
0.2 mgr, corresponds therefore to a known number of sealar divisions. 
The weighing takes place according to the compensation method. 
A cup (fig. 38a) with the tray. (fig. 35) and a number of weights 
is hung on the balance, so that the pointer can freely move along 
the scale; its position is read in the microscope. If the cup is filled 
with substance, the pointer is again brought to about the same 
position by removal of weignts from the tray. After correction for 
different position of the pointer before and after the weighing the 
removed weights show the quantity of substance in the cup, 
expressed in the seale of the ocular micrometer. Before and after 
every weighing the zero position of the balance is determined by 
the aid of a test tray U, which always remains in the balance. 
Every scalar division of the micrometer corresponds to 0.003 mer. and 
allows an estimation down to fourths. To exclude temperature 
influences as much as possible during the weighing, the glass of 
the balance right of the scale is protected by a piece of white 
card-board. 
3. Results. For equation 3 to be applicable, the diameter of 
the dissolved substance must be large with respect to the free path 
Fig. 5. 
