i 9 7 
1880.J New Scientific Processes and Inventions. 
He takes the shales in the state in which they were formerly 
used by the alum and copperas makers. On prolonged exposure 
to air, namely, the sulphur of the pyrites becomes oxidised to 
sulphuric acid, and, attacking both the iron and the clay with 
which it is intimately associated, it forms a mixture of iron and 
aluminium sulphates. The shales are then lixiviated with water, 
and as the solution generally contains an excess of acid it is 
neutralised, as far as possible, by being allowed to stand in con- 
tact with scrap-iron. Being then run off into crystallising tanks 
a very considerable quantity of copperas is deposited. So far, 
it will be clearly understood, M. Fournier is merely following in 
the footsteps of the manufacturers of copperas and alum. But 
now comes the new feature of the process. After the copperas 
has been deposited, the mother-liquor, containing all the 
aluminium sulphate and a portion of iron sulphate, is run off, 
and mixed with common salt in such proportions that there may 
be sodium enough to combine with all the sulphuric acid, and 
chlorine enough to take up all the aluminium and the iron. The 
mixed solution, which should not exceed 23 0 Baume in specific 
gravity, is then exposed to a temperature of - 2° to 3 0 C. In 
what manner this temperature is produced is a matter of indif- 
ference as far as the principle of the invention is concerned. 
When I saw the process worked on the large scale at the esta- 
blishment of M. Raoul Picket, in La Chapelle, the sulphurous 
acid freezing-machine was used with very good results. In a 
short time double decomposition takes place, and we have in 
solution — instead of sodium chloride and aluminium sulphate — 
sodium sulphate and aluminium chloride. As, however, at tem- 
peratures bordering on and a little below o° C., sodium sulphate 
is almost insoluble, it is deposited in the state of a fine crystal- 
line sediment of the deca-hydrated salt (the ordinary form of 
Glauber’s salt), whilst the aluminium and iron remain in solution 
as chlorides. The mother-liquor is rapidly run off, and the de- 
posit is freed from the chlorides mechanically lodged among its 
crystals by washing with brine cooled down to o° C. by an inge- 
nious application of what might be called the waste cold. This 
brine afterwards serves towards the decomposition of the next 
lot of sulphates of aluminium and iron, so that nothing is lost. 
The crystals after washing are freed from moisture in a centrifu- 
gal machine, and are then fit for any purpose to which Glauber’s 
salt is applicable. I have lately learnt from the inventor that he 
has succeeded, at a very trifling cost, in using this salt as a raw 
material for the production of caustic soda. 
We return now to the mother-liquor — a solution of chlorides 
of aluminium and iron. One of the guiding principles of indus- 
trial chemistry is that every result of a decomposition should be 
brought out in a merchantable form. How far can this be carried 
out in the present instance ? To obtain chloride of aluminium 
in a hydrated state a very costly and circuitous process has 
