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Luminous Paint

ONE of the latest and most novel applications of chemistry to the wants of every-day life, is exemplified in the patent taken out by the late Mr. Balmain for the manufacture of luminous paint. There are many things in nature which show the strange phenomenon called phosphorescence. This word has doubtless been chosen to express the appearance of phosphorescent substances, because of their similarity in effect to phosphorus; but chemically they have no connection with that material.

We are all familiar with the luminous appearance of the sea, which is mainly due to a small animal called the notiluca miliaris. The glowworm is still more familiar as a phosphorescent phenomenon; and although it has from time immemorial formed the theme of poets, and the admiration of mankind in general, the manner in which its luminous quality is brought about and exercised still remains a puzzle to scientific men. There are various living things which become luminous, or partly luminous, under certain conditions. In this country a species of centipede, the scolopendria electrica, is, besides the glowworm, one of the best known. But in warmer climes there are various kinds of flies which are so strongly luminous, that they are often placed in ladies' hair as an ornament in place of diamonds or other gems. Certain plants and fungi are sometimes phosphorescent. Among the first may be named the tiger-lily, the nasturtium, and the marigold, all bearing flowers of an orange colour. These have been observed to emit flashes of light at certain seasons and under certain conditions; but it must not be supposed that the appearance is at all common. It is probably due to electricity. The same may be said of those exhibitions of phosphorescence occasionally seen during atmospheric disturbance. The strange phenomenon called St. Elmo's fire, seen on the spars and rigging of ships, will come under this description. So also will the luminous appearance occasionally seen on water-spouts, and the points of fire which have frightened travellers in mountain districts, by appearing upon their bodies during thunderstorms.

We have thus seen that examples of phosphorescence can be gathered from both the animal and vegetable kingdoms. We shall presently show that the mineral world is also rich in similar phenomena.

The first discovery bearing upon this part of the subject, was made by accident by a poor cobbler of Bologna. During some experiments in the vain endeavour to find out the philosopher's stone, by which the base metals were to be turned into gold, he turned his attention to a heavy spar picked up near the outskirts of the city. This was the sulphate of barium, which, by heating with charcoal, he unknowingly converted into sulphide. This mineral is strongly phosphorescent, and the detection of its qualities much surprised its discoverer. This occurred in the year 1602, and nothing more was discovered in the same connection for more than 150 years when Canton first produced the phosphorus which goes by his name. Phosphorus it is not in reality, although it is called, so. It is made by caleining oystershells with sulphur, the resulting compound being sulphide of lime.

The exact preparation of Balmain's luminous paint remains a secret in the hands of a few. It is no doubt a modification of Canton's phosphorus, but is certainly very much more luminous than anything previously produced. The patent merely claims the mixture of a luminous compound, with oil or other media, so that it can be applied to surfaces like ordinary pigment. A few of the uses to which it is proposed to apply it may here be detailed, and we cannot do better than quote the words of Professor Heaton, from the paper read upon the subject before the Society of Arts:-- "Let us now turn to the suggested applications of the paint. They may be roughly divided into the ornamental and the useful, and I need only mention a few out of the many that occur to the mind. In the former class we may include those painted india-rubber balls, which are very pretty, and suggest nocturnal lawn-tennis. Statuary, grotto work, and ornamental tiles, also give striking and beautiful effects. Here is a large bust of the Prince Consort which has been painted and illuminated. You see how fine an effect it produces. Clock faces, so prepared, show the time all night, and watch-boxes enable us to do as much for our watches. The ends of lucifer-match boxes have been painted with the same material. There would obviously be no difficulty in finding one of them in the dark. "To pass to more important applications, the roofs of railway carriages have already been treated experimentally with the paint, with results that appear satisfactory. The light would, of course, only be employed for daylight trains which run through tunnels. Then, again, it is proposed to paint the names of streets, the directions at post-offices, sign-posts, and advertisements, in the same way. Here are some framed notices, "Lodgings to let," and such like, which would easily be seen, at any rate, through a great portion of the night. Still more important is the use of this luminous paint in gunpowder magazines, spirit stores, and for purposes of exploration in coal-mines during seasons of danger, besides many such uses that may be thought of. "But of all the proposed uses of the luminous paint, none seem to me so important, or so certain of practical success, as the marine applications. Several of these have already been realised in a satisfactory manner. For signal and mooring buoys, for instance, its utility is obvious. It is of the utmost importance that the buoys employed for marking channels should be seen easily, the safe entrance to a harbour or river frequently depending upon the successful passage through a line of buoys. The entrances to Poole harbour, and to the mouths of the Thames and Medway, are marked in this way, and great difficulty and danger are often experienced on dark nights in making out the buoys. Now, there can be no doubt that a buoy, thickly-painted with luminous paint, would remain visible through the whole, or nearly the whole, of a night. A few evenings ago I assisted at the trial of a small mooring buoy at Erith. It was not placed in the water till nine at night, having, of course, been for some hours before in darkness. We found that it was easily visible at distances of over a hundred yards, although the night was not a clear one, and the light, to which the buoy had been exposed, had not been very good. Yachtsmen, returning to moorings late at night, would find such buoys a great advantage, and many collisions might, in this way, be avoided. Equally important is the application of this paint to life-buoys. Life-buoys are, or should always be, kept on deck in convenient situations. A life-buoy thrown to a man overboard will often save his life, particularly if the man can swim. But what is the use of throwing out a common life-buoy on a dark night ? It is impossible for the man to see it, and it is equally invisible to those on board. Here is a life-buoy painted with luminous paint. It has been on the roof of this house all day, and has, consequently, been now several hours in darkness, yet you see it emits a light that could easily be seen at a very considerable distance. Any decently good swimmer could easily reach it, while the ship's boats would know at once the point to which they must row. "Finally, there seems no doubt of the usefulness of the paint in diving and other submarine operations. We have ready a diver in full dress, painted all over with the luminous paint. He is being illuminated in the next room. Now he enters, and you see what a brilliant and ghost-like appearance he presents. At present one of the greatest difficulties in submarine operations arises from the intense darkness. With this new arrangement every diver will be his own lanthorn, and will carry down with him a stock of daylight that will assist his labours materially. This dress was actually so used at Southampton a day or two ago. Mr. Philip Hedger, the Superintendent of the Southampton Dock Company, has sent a letter to Messrs. Ihlee and Horne, in which he says, that the diver descended, on a somewhat murky day, into twenty-seven feet of not very clear water, and found that he was able to distinguish the bolt heads and muscles on a ship's-bottom with ease. Mr. Hedger seems to entertain no doubt of the success of the new application."

It will be gathered from the foregoing that the luminous paint requires exposure to sunlight, or some artificial source of illumination before it becomes phosphorescent. Magnesium wire is, perhaps, the most effectual agent for this purpose. The cost of the paint is at present twenty-eight shillings per cwt., but no doubt exists that it will become cheaper as the demand increases.