179 
variations. As however this slight variation sensibly affects 
the rate of f oav through the siphon, the apparatus is slightly 
modified as follows. Between the reservoir B with its flask A 
and the dripping sphere a second reservoir W is placed. This is 
kept in a s:atc of continual overflow. The overflow is regu- 
lated by means of a few filaments of cottonwool hanging over 
the edge of the overflowing vessel and so fashioned that the 
thickest part of the cotton plug is in contact with the edge. 
Finally the rate of flow is so sensitive that it is impossible to 
procure an exact and predetermined rate by the ordinary 
screw adjustement of the holder which carries the siphon. 
For the final adjustment it is convenient to depend upon the 
elasticity of the siphon which is at first rigidly fixed so as to 
deliver the liquid at nearly the required rate. A heavy ring is 
then slipped on the siphon so as to bend it more or less. A 
little caoutchouc is wrapped round the ring where it touches 
the glass so as to prevent it from slipping. See Fig. III. 
The following table shows how the size of a drop is affected 
by the quantity of solid matter which it, holds in solution. 
The liquids examined were solutions of chloride of calcium 
of different strengths. They Avere prepared as folloAA's : — 
A solution nearly saturated (at 28 ° C.) Avas taken as the 
starting point. Solution 1. An accurately stoppered bottle Avas 
tAA'ice filled vrith solution 1, emptied into a beaker and mixed 
with tAvo bottles of Avater. This gave solution 2. Half of this 
was kept and the rest, mixed again with its own volume of wa- 
ter gave solution 3 and so on. In this Avay without knoAV- 
ing the strength of solution 1 : Ave knoAv that the successive 
strengths of the solutions whether there be loss of volume, due 
to chemical combination, or not, are as S, 
S S S S S 
0 
} -4 ) 8 j 16 > 32 
These numbers give exactly the relative quantity of solid 
matter in a unit of volume of the liquid. As however solution 
I on dilution evolves heat, the sizes of the drops cannot be 
derived from their Aveiglit directly. The specific gravity of 
each solution has to be determined. 
