Phosphorescence

A number of bodies have the peculiarity under certain circumstances of emitting light, the origin or cause of which has not as yet been fitly explained. Among such cases is the appearance of light during the process of crystallization. The transition of a substance from the non-crystallized, amorphous or liquid, to the crystallized condition, is accomplished by a simultaneous movement of its atoms, producing light in a manner which cannot be further accounted for.

In all cases to be mentioned, it will be found a very remarkable fact that when the substance has once shown this phenomenon, during its passage into the crystallized state, it will not show it again when redissolved and recrystal-lized. Evidently there is connected with it a positive change in the arrangement of the atoms, and the phenomenon of phosphorescence is only in so far coincident with the process of crystallization, as the latter is produced by a rearrangement of the atoms.

The amount of light developed is in all instances so small as to be observable only in the dark.

Arsenious Acid

This substance, as it appears when freshly prepared, and partly even for some length of time afterwards, is in transparent, glassy, perfectly colorless lumps. It gradually passes, beginning on the outside first, into a semi-transparent porcelain like, and finally into a perfectly opaque state. This change is caused by the atoms assuming the form of crystals. It is reduced more rapidly and with the appearance of light when the crystallization of the acid takes place from a solution of it. For this purpose a piece of the transparent arsenic is powdered and dissolved in somewhat dilated and boiling hydrochloric acid to saturation, with due observance of the caution necessary to guard against accidental poisoning. The glass vessel containing the solution is then allowed to cool slowly, having been placed on some non-conducting substance, such as wood. As soon as the crystallization sets in, the formation of each crystal is observed in the dark by a brilliant glimmer of light.

Sulphate Of Potash

The neutral sulphate of potash, when freshly prepared, possesses the same property of phosphorescence while passing into the state of crystallization. It is necessary that the solution of this salt be not made by dissolving crystals of it in water, but that it be a solution of its components sulphuric acid and potash, or bisulphate of potash and potash. For, the once crystallized salt has already undergone the change in the atoms on which the success of the experiment depends, and its immediate formation, as it were, an amorphous condition, is indispensable. To a solution of purified pearlash or salt tartar in hot water, dilate sulphuric acid is added gradually, as long as effervescence takes place, or the liquid turns red litmus paper to blue, then filtered and evaporated to the point of which, a small portion of it on cooling deposits crystals. The solution is then allowed to cool slowly in an open dish, and it will show in the dark a constant succession of viscid flashes attending the formation of crystals.

Better results are sometimes obtained by neutralizing a solution of fused bisulphate of potash with pearlash in the same manner.

Sulphate Of Soda And Potash

A mixture of 11 parts of sulphate of potash and 9 of effloresced sulphate of soda is fused in a crucible, then allowed to cool, powdered, dissolved in just enough hot water, and quickly filtered. On cooling, the formation of crystals is accompanied by a similar phosphorescence as that above referred to. Within a few hours after their formation they will shine again when rubbed; but on being redissolved and again brought to crystallization, no light will be observed, nor would any be seen in the original solution if it were too dilute when first made, and had to be evaporated.

Sulphate Of Potash And Carbonate Of Soda

A mixture of 8 parts of sulphate of potash and 3 of effloresced carbonate of soda, fused and treated in the same manner as the above, gives the same result.

Chromate Of Potash And Sulphate Of Soda

A mixture of 19 parts of neutral chromate of potash and 14 parts of effloresced sulphate of soda gives the same result as above.

Chromate Of Potash And Soda

The following mixture behaves in the same manner: 2 parts of bichromate of potash and one of dry carbonate of soda. In this case the crucible must be large enough to allow for the effervescence caused by the disengagement of carbonic acid.

Benzoic Acid

The sublimation of benzoic acid is attended by a brilliant exhibition of glimmering lights when properly conducted. An optional quantity of it is mixed with one-sixth of its weight of powdered charcoal, and put into a flat dish which is placed on a heated iron plate; the dish is covered by a large bell glass.