ELECTRICAL CONDUCTIVITY OF FERRIC SULPHATe SOLUTIONS.
1027
of the oxides which dissolve water and that no definite basic phosphates or silicates form. The curve for alumina and phosphoric acid shows a decided drop a t the point corresponding to AlPO,, the curve rising on either side. This compound probably forms but we do not consider the result conclusive. We wish to express our thanks to the Committee for the C. 11. Warren Fund of the American Academy of Arts and Science for a liberal grant enabling us to carry out this work. S H E F F l ELI3 LABORATORY,
NEWHAVEN,CONI?.
THE ELECTRICAL CONDUCTIVITY OF FERRIC SULPHATE SOLUTIONS. BY R O G E R C. WELLS.
Received July 15, 1909.
The interesting behavior of ferric sulphate solutions when diluted or heated has been studied by several investigators chiefly with the desire to find out the composition of the basic precipitates thus formed.2 The present paper contains data upon the electrical conductivity of these solutions. The conductivity method has been shown to be an excellent help in following changes in solution and the results here given may prove useful in working out a theory of the state of ferric sulphate in solution. Preparation. o j Neutral Ferric Sulphate.-When ordinary ferric sulphate is dissolved in water the solution usually contains an excess of acid. Maus, long ago, however, pointed out the interesting faot that such a solution, if moderately concentrated, will dissolve ferric hydroxide. I t is therefore an easy matter to secure a solution which will analyze “neutral” by first saturating the ordinary solution with ferric hydroxide and then adding sulphuric acid to neutrality. &4little ferric hydroxide was precipitated and very thoroughly washed for this purpose. After agitation with the ferric hydroxide and filtration the ferric sulphate solution gave on analysis 0.4239 gram equivalent Fe,O, per liter and 0.4115 gram equivalent SO, per liter. After adding the calculated amount of sulphuric acid an analysis gave 0.4173 gram equivalent Fe,O,, 0.4126 gram equivalent SO,. A final addition of acid brought up the concentration to 0.4173 gram equivalent Fe,O,, and 0.4170 gram equivalent SO, per liter, which was the solution used in all the experiments here described. Apparatus.-The measurements were made with the usual conducPublished by permission of the Director of the U. S. Geological Survey, Scheerer, Pogg. Ann., 44, 453 (1838). Pickering, J . Chem. Soc., 37, 807 (1880). Moissan, Trait6 de chintie minerale, 4, 375,
* Pogg. Ann., IT, 75 (1827).
I028
GENERAL. I'NYSICAI,
.\SD INORGANIC.
ti\-i t v ,tpparatiis ' The electrically heated and regulated thermostat con\tatit t o i t 02' I:ot larRe 1 ciluniei of solution dip electrodes Mere c'onst~iictetl I t \ \ a \ foiiiicl \ erl; importarit t o determine the cell \?a\
Fig. l
I.
Ostwald-Luther, Plivsik-clieni., Messungen, 11. 30,?
ELECTRICAL CONDUCTIVITY OF FERRIC SULPHATE SOLUTIONS.
IO29
factors with exactly as much solution and with the electrodes in the same position as obtained in actual measurements. Pure potassium chloride was made up to 0 . 0 2 N for determining the cell factors. Sufficiently pure water was employed to make the correction a very small fraction in most cases. I n the tables v represents the number of liters containing a gram equivalent of salt (1/6 Fe,(SO,), in grams) and A = 1000K v the equivalent conductivity where K is the specific conductivity. T h e Behavior of Ferric .%@hate on DiEution.---When a concentrated solution of ferric sulphate is diluted a precipitate appears on standing or warming which has usually been designated "basic salt." I t contains ferric oxide and sulphate. The composition of such "basic salts" has been shown by Cameron and Robinson to be indefinite.' The formation of this precipitate, however, is sufficient evidence of the tendency of dilute ferric sulphate to hydrolyze. Furthermore, one would certainly expect the hydrolysis of ferric sulphate to occur from analogy with ferric chloride. The latter salt has been studied by Goodwin,, who found that the conductivities of the dilute solutions increase with time, a phenomenon becoming very marked a t high dilutions and accompanied by the formation of a yellow precipitate. Similar changes occur with ferric sulphate. By the method of successive dilutions values were obtained for the conductivity up to v = 16 a t 2.5' without observing any irregularity. At higher dilutions a slow increase became evident, much more marked a t higher than a t lower temperatures. Time curves for such observations were obtained for a number of dilutions and temperatures. The results are given in Table I and some are plotted in Fig. I . TABLEI. Equivalent conductivity.
Time.
v = 19.12 t = 25O
I min. a f t e r diluting. 15 rnin. 30 "
57.2
5 days 8 "
82.3 82.3
min.
i3.2 53.6 73.9 96.9 97.6
v = 25.15
0.66 rnin.
t
2
((
4
'(
15
"
57.7 57.8 69.7 70.3 70.5 70.7
38
"
71.2
44
71.3
hi. hr. 4hr. 6 hr. 18 hr.
=
30°
I hr. 16 rnin. 4 hrs. 26 rnin. 6 hrs. 6 min. 18 hrs. 3 days
72.2
73.2 77.2 80.0
J . Physic. Chem., 11, 641 (1907). 2.Physih. Chem., 21,
I (1896).
Equivalent conductivity.
Time.
v = 38.24 t = 250 = 61.12 t = 30° V
I
4
"
IO
"
I
"
3 27
"
IO0
"
IO1
I
I
"
13 min. 48 " 53 38 " ' I
103 106 117 121
131
,
1030
GENERAL, PHYSICAL AND INORGANIC.
TABLEI (Continued). Time. 22
hr.
8 min.
3 days
8
61.12 t = 30°
"J
=
9
I'
25
min.
I ?
"
61
j'
122
' I
32
''
2 = 201
t = 30°
"
I11
"
248
''
80
hrs. I . 5 min.
I10
2.7
4
"
7
"
29 48
'I
' I
= I21 t = 30°
?I
2.51
3.5 4 . j9 9
t = 30°
t
=oo
v = 300 t = 290
"
? j?
78.4 79.5 80.4 80.4 81.6 84 I 18
Ia
(6
I2j
2
"
149
4
('
8
I'
* 94
156
214
36
"
2 36
"
-
v = 300
I
t
2
'i
105
3
"
206
I
'/
I bo
1
1'
202
5
' I
30°
v = 300 1 = 30°
"
7
245
"
min.
i'
215
hrs. j days 2 min. 4 (' 6 " 9 I' 16 " 386 " 0 . 5 min.
201
"
3 4 -
205 "
"
'' ''
24
I'
150 '64 173 181 189 197
"
"
I
"
176
1;
26 36
169 I. 75
IO
21
42 52 = IjI
= 300
58
'I
14
'u
"J
::
73 131 140 158 3 days 6 " 0 . j min. 1.5 "
"
20
'I
f
I60
2
4 8 17 38
I'
' I
38 " '( 43 0.66 min.
53 104
22
v = IO1 t = 30°
Equivalent condnctivity.
Time.
" ' I
3
Solution clear. Ppt. appears. Ppt. visible. ' Ppt. Solution remains a clear very pale yellow.
s
min.
' I
16
''
27
'1
61 " 99 119 ' ' 18 hrs. 3 days /'
11.9
212
219 128 242
258 265
269 294 303
ELECTRICAL CONDUCTIVITY OF FERRIC SULPHATE SOLUTIONS.
103I
TABLEI (Continued). Equivalent conductivity.
Time.
4 days. 7
v
= 600
t =oo
t
-
min.
a IO
('
98.7 98.3 99.5 107.7
14
"
117
0 . 5 min.
202
I10
226
I
"
229
2
((
"
237
5
' I
min.
3 6 39 119'
= 600
G
306 302
99.6
I
9
v
Time,
~ 8 . 9 ~ 1.5
3 4
'I
" "
"
v t
= 600 = 30°
I
I'
"
2
"
3
"
19
" I'
day
Equivalent conductivity.
248 236 240 246 247 2 60 266 295 327 353 337 342
The True Conductivities of Ferric Sulphate Solutions.---If the curves
Fig. 2. Solution shows a very pale yellow opalescence.
1032
GENERAT,, PHYSICAT, .4ND INORGANIC
derived from the above measurements are considered it will be seen that it is possible to estrapolntr \,slues lor the conductivities at zero time which m a y rensonabll; be taken a s the conductivities of ferric sulphate soiuticiis." 'l'hese c:ztrapolatecl \-slues form a continuous curve with those obtained by the metiiod of successi\-e dilutions of the concentrated solution. f3>- repetition. fairly concordant \-slues were thus obtained and are plotted in Fig. 2 lor the temperatures 0'. 25' and 30'. The c~irx-esenable one to read oli' the values for the conductivity a t the customary dilutions arid also sliow the temperature coefficient of the conductivity a t the various dilutions. Tlie data iron1 which the first part of the curves are plotted arc gi\-en in 'l'able IT. s.
TABLEI1 Equivalent conductivity.
36.19 45.33 j7.2 i3.2 26.24 25).
