19 
On the Crystallization of the Sulphates of Iron, 
Cobalt, and Nickel. By Robert Thomas. 
(Read January 9th, 1867.) 
The object in view, in crystallizing the salts of the mag- 
netic metals, being to ascertain whether there is any relation 
between the magnetic principle in those metals and the action 
which takes place in the crystallization of their salts, ex- 
periments have been made with a less number of atoms of 
water than are usually found in the natural crystals of these 
salts, and the results of these experiments are here submitted 
as indications of the possibility that some such relations 
exist. 
Faraday has shown* that a crystal of sulphate of iron “is 
compounded of superposed flat crystals or plates, and that 
the magne-crystallic axis goes directly across these.” After 
many trials, the writer has been able to get these “ plates ” 
to form on the “ slide,” which may be done as follows : — 
Take a concentrated solution of sulphate of iron, with a small 
quantity of sugar to prevent oxidation of the film of iron. 
Drive off the water as rapidly as possible with a “ Bunsen's 
burner ” or “ spirit-lamp,” and when nearly dry the “ plates ” 
will form, and, if carefuily watched, their formation may be 
seen even by the unaided eye. Then place the slide quickly 
at a higher temperature, and further crystallization of the 
plates will be arrested. When perfectly dry, the slide should 
be kept at a temperature of about 65° Fahr. ; but these pro- 
cesses (even when great care is taken) are influenced much 
by the state of the atmosphere. If it be too moist, the 
foliation (seen in the specimens) will proceed from all points 
of the “ plates.” The slide should then be placed at a higher 
temperature, when the foliations will proceed only from each 
pole, or from the ends of the longest diameter of the plates, 
and curve backwards towards the opposite pole, exhibiting 
the same configurations as iron filings when arranged round 
the magnet, the crystalline force appearing to flow in the 
direction of the magne-crystallic axis described by Faraday. 
Specimens of the crystals of the salts of cobalt and nickel 
are also shown, which clearly indicate that they all have the 
same mode of formation as, but less definitely marked than, 
those of iron. And if the relationship to which reference has 
been made should be found to exist, this less perfect crystal- 
* Series xxii, § 2546. 
