370 Proceedings of the Royal Society of Edinburgh. [Sess. 
III. A Synthetic Silicate Resembling Glauconite. 
Some attempts by Calderon and Chaves, quoted by Collet and Lee,* to 
synthesize glauconite-like silicates seem to have led to no very definite 
results. By means of the method now to be described, a substance very 
similar to glauconite may be prepared in the laboratory. The principle 
consists in allowing colloidal solutions of a complex ferric radical to react 
on an alkaline silicate solution. 100 cc. of a 10 per cent, solution of 
potassio-ferric tartrate (corresponding to 2*4 gr. Fe 2 0 3 ) are added to 50 cc. 
of a solution of potassium silicate containing 1-2 gr. Si0 2 . The mixed 
liquids immediately assume a greenish-blue colour, and in a very short time 
set to a clear stiff jelly. The jelly is broken up and heated under pressure 
to 180° for 6-8 hours, the result being a magma of green flocculent particles 
in a colourless mother-liquor. These particles are washed by decantation 
with dilute acid, dilute alkali, and water, then filtered off and dried. 
The substance thus obtained is a double silicate of potassium and iron. 
A portion of the latter is in the ferrous state : the double tartrate was 
originally not quite free from ferrous iron, and a further partial reduction 
of ferric iron would seem to have taken place in the heating operation. 
Under the microscope the substance appears quite amorphous and, except 
for a slight variability in the colour of the particles, homogeneous. It is not 
readily attacked by alkalies or cold dilute acids ; warm dilute acids, how- 
ever, slowly decompose it, in which respect it is rather less resistant than 
glauconite. The colour of the substance is grass-green, but the tint fluctuates 
somewhat in different preparations. That the green colour is due to ferrous 
iron is indicated by the fact that solutions of a hypobromite, or of hydrogen 
peroxide, discharge the colour of the silicate, converting it into a straw- 
coloured substance. 
Chemical analysis after drying at 110° gave the following figures : — 
Ignition loss . . . . . . 4T9 
Si0 2 . 56-80 
Fe 2 O s 28-16 
Fe() 4-16 
K 2 0 ...... 7-27 
100-58 
In composition, therefore, this silicate is not unlike natural glauconite, 
the chief differences being that it is more acid and contains much less 
water of hydration. Whilst it is not pretended that its formation and 
* Loc . cit ., p. 263. 
