Osmotic growths of ferrocyanide of copper.
Osmotic growths may be obtained from a great number of chemical substances. The most easily grown are the soluble salts of calcium in solutions of alkaline phosphates and carbonates, to which we have already alluded. We may also reverse the phenomenon by growing phosphates and carbonates in solutions of calcium salts, but in this case the osmotic growths are not so beautiful.
The various silicates play an important part in the constitution of shells and of the skeletons of marine animals. Most of the metallic salts, and more especially the soluble salts of calcium, give rise to the phenomenon of osmotic growth when sown in solutions of the alkaline silicates. In this way, by using different silicates and varying the proportions and the concentrations, we may obtain an immense variety of osmotic growths.
A good solution to commence with is the following:—
| Silicate of potash, sp. gr. 1.3 (33° Beaumé) | 60 gr. |
| Saturated solution of sodium carbonate | 60 gr. |
| Saturated solution of dibasic sodium phosphate | 30 gr. |
| Distilled water | make up to 1 litre. |
A fragment of fused calcium chloride dropped into this solution will produce a rapid growth of slender osmotic forms which may attain a height of 20 or 30 centimetres.
Small pellets may also be made of one part of sugar and two of copper sulphate and sown in the following solution, which must be kept warm until the growth is complete:—
| Ten per cent. solution of gelatine | 10 to 20 c.c. |
| Saturated solution of potassium ferrocyanide | 5 to 10 c.c. |
| Saturated solution of sodium chloride | 5 to 10 c.c. |
| Warm water (32° to 40° C.) | 100 c.c. |
In this solution we can obtain osmotic growths which may attain to a height of 40 centimetres or more, vegetable forms, roots, arborescent twigs, leaves, and terminal organs. These growths are stable as soon as the gelatine has cooled and set, and may be carried about without fear of injury (Fig. 35).