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of the three first cups; its mean value furnished the initial quantity. 
The increases in weight of K4 >; yielded the diffusion rests. 
The cups were weighed in the balance represented in fig. 4. The 
preparation of a micro balance suitable for our purpose has presented 
many difficulties; after a great many futile attempts we have suc- 
ceeded in making an efficient apparatus, with which all the experi- 
ments described below have been carried out, and which has proved 
very satisfactory. The balance consists of a wooden bottom "4, 
provided with three levelling screws and a detachable wooden case 
B, the front side of which consists of glass. The balance rests on 
a board C, which is placed with three rubber stops on the wall 
bracket D. On the bottom lies the glass plate /, on which the 
stand /’ has been cemented. The beam G consists of a thin glass 
rod provided with a piece of a razor, which is fastened to the 
beam with sealing wax, and rests free on the glass plate //7. One 
extremity of G ends in a thin glass fibre /, which moves along a 
scalar division on the celluloid plate A. To the other extremity of 
the beam is fastened a very thin quartz thread 4, provided with a 
glass hook M, which serves for the suspension of the cups. The 
beam is restricted in its movement by the horizontal glass rods MN 
and O, so that only small oscillations are possible. Further the 
plumb P, hanging over a mark on the bottom, the drying vessel 
with concentrated sulphuric acid Q, and the plate #, which serves 
for the adjustment and removal of the cups, are indicated in the 
figure. During the weighing no displacement of the razor in the 
direction left-right takes place on careful manupilation, at least if 
the plate 7 has beer placed quite horizontal by the aid of a level 
or a ball from a cycle bearing; the only movement that takes place 
is a small rotation round the vertical axis which removes the pointer 
somewhat from the scale AK. The glass tube S serves to keep this 
distance always very small, which is required for the reading of 
the position of the pointer in the microscope, which stands horizon- 
tally before A. Tube S ends in a very thin glass thread, and can 
be rotated by a handle outside the case. [f a movement of the beam 
in the direction left-right should have taken place, the original 
position can be restored by bringing the beam on Q and the cork 
disk of 7, which can again be rotated round a horizontal axis from 
the outside, and can be slid in and out. Accordingly the balance 
case need only be removed for the refreshing of the drying substance 
Q. The microscope has an ocular micrometer; the value of the scalar 
divisions K is expressed in that of the micrometer as unity. The 
weights used are likewise gauged by means of the ocular micrometer. 
