557 
of Edinburgh, Session 1874 - 75 . 
each of the three experimenters mentioned had used in all his 
(or their) observations a method quite different from that of the 
others; and that, while the results of one pair on zinc-vitriol 
agree, the results of the other pair on dilute sulphuric acid also 
agree. Kohlrausch and Nippoldt’s determinations are used as a 
medium of connection between those of the other two ; and only 
on the supposition that they used throughout the same method or 
methods connected by compared results, can they reasonably be 
used as such, or the agreement between Kohlrausch and Nippoldt 
and Paalzow be supposed to assist in establishing the accuracy 
of Professor Beetz’ results. What, then, are the facts ? Professor 
Beetz has made a series of observations of the conductivity of zinc- 
vitriol solutions; Paalzow, of dilute sulphuric acid. Kohlrausch 
and Nippoldt have investigated solutions of' both, but with different 
and unconnected, methods . In all cases in which they investi- 
gated zinc sulphate they used Professor Beetz* method. The 
principle of his method is the use of non-polarisable electrodes ; 
that of Kohlrausch and Nippoldt’s, the reduction of polarisation 
by means of rapidly alternating currents and large electrodes to 
as small an amount as possible. In one determination their 
mode of investigation was quite the same as Professor Beetz’ ; * 
in the other they used magneto-electric alternating currents in- 
stead of the ordinary galvanic current. f It is evident, however, 
that, even in this determination, since they used amalgamated 
zinc electrodes and not platinum ones, they were working with 
Professor Beetz’ method and not their own ; for the alternating 
currents are characteristic of their method, only in so far as 
they prevent the heaping-up of the polarising substances on 
platinum or other polarisable electrodes. A link is wanting, then, 
between the methods used by Kohlrausch and Nippoldt in their 
sulphuric acid determinations and their zinc sulphate determina- 
tions respectively. Nor is this link supplied by the comparison of 
methods given by Kohlrausch and Grotrian ; $ for they make only 
a single comparative observation, and their platinum electrode 
method is an improvement upon that of Kohlrausch and Nippoldt. § 
There being no connecting link, Professor Beetz cannot cite 
* Pogg. Aim. cxxxviii. p. 376. t Ibid. p. 373. 
X Ibid. cliv. p. 10. § . Ibid. p. 2. 
