ELECTRICAL CONDUCTIVITY OF CERTAIN SALINE SOLUTIONS. 55 
3, xvii.), in which he announced the same discoveries as HANKEL. He went into 
the subject much more fully than HanKeEt did, and his method was also better 
than the previous one. It was based on a suggestion of WHEATSTONE’s, and 
depended, like that of HANKEL, on the use of the differential galvanometer. 
But instead of having only one tube of the solution, BEcQUEREL had a tube in 
each circuit. After adjusting the length of the tubes so that no deflection was 
produced, he then introduced a coil of known resistance into one circuit, and 
shortened its tube so as to bring the needle again to zero. Then the resistance 
of the wire was equal to that of the column of liquid by whose length he had 
shortened that tube. This method was an improvement on that of HANKEL, in 
so far as it did away with, or at least diminished the effect of polarisation—a 
phenomenon, however, to which BEcQUEREL seems to have paid little attention, 
and to which he appears to refer in the expression, “la resistance au passage 
des solides dans les liquides.” But it was open to one grave objection, namely, 
that the current employed was of sufficient intensity to cause a very perceptible 
electrolysis of the liquid during the time it was being tested. This difficulty 
has been overcome by the use of the mirror galvanometer in the mode of test- 
ing we have employed. 
The results obtained by BEcQUEREL are summed up by him as follows :— 
“Saline solutions may be divided into two classes with regard to, conductivity. 
The first includes those solutions whose conducting power increases with the 
degree of concentration up to the point of saturation, such as sulphate of copper 
and chloride of sodium. ‘The second includes the solutions of deliquescent salts, 
_ or those which are exceedingly soluble in water, and whose conductivity at first 
increases with the degree of concentration, soon attains a maximum, then 
diminishes as the concentration increases; sulphate of zinc and nitrate of copper 
belong to this class. 
“If we represent by C the conductivity, and by g the quantity of salt dis- 
solved in unit volume of the solution, we have the equation— 
it . B 
C (or R, the resistance) = A + me 
A and B being two constants for the same salt at a constant temperature.” 
This equation, he says, applies to the solutions of the second class only from 
a very weak solution up to that of maximum conductivity. BECQUEREL’s results 
are often quoted as conclusive on the subject of the conductivity of liquids. 
The next experimenter was Horsrorp (Pogg. Ann., lxx., 1847). His 
method was no improvement on those of his predecessors, but rather the re- 
verse, as polarisation was not properly eliminated. His experiments were 
chiefly made on sulphuric acid and the metallic chlorides. 
VOL. XXVII. PART I, iE 
