Beautiful Crystals.—Pour three ounces of diluted nitric acid into a glass vessel, and add gradually to it two ounces of bismuth, broken by a hammer into small pieces. The metal will be attacked with great energy, and nitrate of bismuth will be formed. Crystallize the solution by a gentle heat, and preserve the crystals, which possess great beauty, under a glass.
The Centre of Gravity.—A shilling may be made to balance on the point of a needle with very simple apparatus. Put a bottle on the table with a cork in its neck; into the cork stick a middle-sized needle in an upright position. In another cork cut a slit, and insert the shilling, then into this cork stick a couple of forks, one on each side, with the handles inclining outwards. Now poise the rim of the shilling upon the point of the needle, and it will rotate without falling. So long as the centre of gravity is kept within the points of support of a body it cannot fall. The balancing shilling may be transposed to the edge of a bottle, and it will still perform, even as the bottle is being tilted.
What a Vacuum Can Do.—Take a new or nearly new penny and rub it briskly upon your coat sleeve until it is warm. Then slide it up and down upon a door panel, pressing it closely to the wood. Now hold it in one place for a few seconds and you will find it will stick there, because between the penny and the surface of the door there is a layer of air which was slightly heated. As it became cool a partial vacuum was formed, and the pressure of the outer air held the penny to the door.
An Experiment in Leverage.—It would seem almost impossible that a column of iron or a plank or a spar of any kind could be so placed that one end of the spar needs support only, whilst the other end would extend from, say the edge of a precipice, horizontally into space; but that such can be done is very easily demonstrated, by very simple materials almost always at hand. By adopting the principle we may easily perform an interesting scientific parlour experiment, which always causes difficulty to the non-studious section of humanity, until the apparent mystery is explained.
In illustrating this experiment the prongs of two ordinary table forks are fastened together, one over the other—net fashion—thus causing the handles of the forks to form the termini of an angle of about 45 degrees. Now take an ordinary lucifer match and place one end between the network of the prongs firmly. Then place the other end of the match upon the edge of an elevation, such as a tumbler or cup, when the match, acting as a lever, with the forks giving a hundred or a thousand times additional weight to the lever, will rest (or apparently float in the air) without further support.
Ask your friends to try the experiment, after placing the materials before them, and find how many can perform it without guidance.
Coloured Fires.—It is perilous to make some coloured fires, especially those in which there is sulphur, and even if they do not explode their fumes are harmful, so that their use in the house for charades or other home purposes is objectionable and at times positively dangerous. We give, however, a number of coloured fires that are free from these drawbacks, though all the same it is wiser to reduce the ingredients to powder quite separately before they are mixed, and if a pestle and mortar are used all traces of one powder should be removed before another is introduced. Each ingredient should be reduced to a fine powder.
| Red Fire. | |
|---|---|
| Parts. | |
| Strontia | 18 |
| Shellac | 4 |
| Chlorate of Potash | 5 |
| Charcoal | 4 |
| Green Fire. | |
| Nitrate of Barytes | 18 |
| Shellac | 4 |
| Calomel (Chloride of Mercury) | 4 |
| Chlorate of Potash | 2 |
| Green Fire. | |
| Nitrate of Barytes | 9 |
| Shellac | 3 |
| Chlorate of Potash | 12 |
| Charcoal | 4 |
| Blue Fire. | |
| Chlorate of Potash | 14 |
| Salpetre | 6 |
| Ammonia Sulphate of Copper | 6 |
| Arsenite of Copper | 6 |
| Shellac | 2 |
| Blue Fire. | |
| Ammonia Sulphate of Copper | 8 |
| Chlorate of Potash | 6 |
| Shellac | 1 |
| Charcoal | 2 |
| Red Fire. | |
| Nitrate of Strontia | 9 |
| Shellac | 3 |
| Chlorate of Potash | 1½ |
| Charcoal | 4 |