Fig. 316.—Gold-leaf exposed to the fumes of mercury.
A very ingenious little lamp may be constructed which lights of itself without the help of a flame. It contains a bell of glass, which is filled with hydrogen gas, produced by the action exercised by a foundation of zinc on acidulated water. If the knob on the upper part of the apparatus is pressed, the hydrogen escapes, and comes in contact with a piece of spongy platinum, which, acting by oxidation, becomes ignited. The flame produced sets fire to a small oil lamp, which is opposite the jet of gas. This very ingenious lamp is known under the name of Gay-Lussac’s lamp. Platinum can also produce, by mere contact, a great number of chemical reactions. Place in a test glass an explosive mixture formed of two volumes of hydrogen and one volume of oxygen; in this gas plunge a small piece of spongy platinum, and the combination of the two bodies will be instantly brought about, making a violent explosion. Make a small spiral of platinum red-hot in the flame of a lamp, having suspended it to a card; then plunge it quickly into a glass containing ether, and you will see the metallic spiral remain red for some time, while in the air it would cool immediately. This phenomenon is due to the action of oxidation which the platinum exercises over the fumes of ether. This curious experiment is known under the name of the lamp without a flame. This remarkable oxidizing power of platinum, which has not yet been explained, was formerly designated by the title of catalytic action. But a phrase is not a theory, and it is always preferable to avow one’s ignorance than to simulate an apparent knowledge. Science is powerful enough to be able to express her doubts and uncertainties boldly. In observing nature we find an experience of this, and often meet with facts which may be put to profit, and become useful in application; nevertheless it is often the case that the why and the wherefore will for a long time escape the most penetrating eye and lucid intelligence. It is true the admirable applications of science strike us with the importance of their results, and the wonderful inventions they originate; but if they turn to account the observed facts of nature, what do they teach us as to the first cause of all things, the wherefore of nature?—Almost nothing. We must humbly confess our powerlessness, and say with d’Alembert: “The encyclopædia is very abundant, but what of that if it discourses of what we do not understand?”
Fig. 317.—Discolouration of periwinkles by sulphuric acid.
Artificial Colouring of Flowers.
In a course of chemistry, the action exercised by sulphurous acid on coloured vegetable matter is proved by exposing violets to the influence of this gas, which whitens them instantaneously. Sulphurous acid, by its dis-oxidating properties, destroys the colour of many flowers, such as roses, periwinkles, etc. The experiment succeeds very readily by means of the little apparatus which we give in fig. 317. We dissolve in a small vessel some sulphur, which ignites in contact with air, and gives rise, by its combination with oxygen, to sulphurous acid; the capsule is covered with a conical chimney, made out of a thin sheet of copper, and at the opening at the top the flowers that are to be discoloured are placed. The action is very rapid, and a few seconds only are necessary to render roses, periwinkles, and violets absolutely white.
Fig. 318.—Experiment for turning columbines a green colour with ammoniacal ether.
M. Filpol, a distinguished savant, has exhibited to the members of the Scientific Association, Paris, the results which he obtained by subjecting flowers to the influence of a mixture of sulphuric ether and some drops of ammonia; he has shown that, under the influence of this liquid, a great number of violets or roses turn a deep green. We have recently made on this subject a series of experiments which we will here describe, and which may be easily attempted by those of our readers who are interested in the question. Some common ether is poured into a glass, and to it is added a small quantity of liquid ammonia (about one-tenth of the volume). The flowers with which it is desired to experiment are then plunged into the fluid (fig. 318). A number of flowers, whose natural colour is red or violet, take instantaneously a bright green tint; these are red geranium, violet, periwinkle, lilac, red and pink roses, wall-flower, thyme, small blue campanula, fumeter, myosotis, and heliotrope. Other flowers, whose colours are not of the same shade, take different tints when in contact with ammoniacal ether. The upper petal of the violet sweet-pea becomes dark blue, whilst the lower petal turns a bright green colour. The streaked carnation becomes brown and bright green. White flowers generally turn yellow, such as the white poppy, the variegated snow-dragon, which becomes yellow and dark violet, the white rose, which takes a straw colour, white columbine, camomile, syringa, white daisy, potatoe blossom, white julian, honeysuckle, and white foxglove, which in contact with ammoniacal ether assume more or less deep shades of yellow. White snap-dragon becomes yellow and dark orange. Red geranium turns blue in a very remarkable fashion; with the monkey-flower the ammoniacal ether only affects the red spots, which turn a brownish green; red snap-dragon turns a beautiful brown; valerian takes a shade of grey; and the red corn-poppy assumes a dark violet. Yellow flowers are not changed by ammoniacal ether; buttercups, marigolds, and yellow snap-dragon preserve their natural colour. Leaves of a red colour are instantly turned green when placed in contact with ammoniacal ether. The action of this liquid is so rapid that it is easy to procure green spots by pouring here and there a drop of the solution. In like manner violet flowers, such as periwinkles, can be spotted with white, even without gathering them. We will complete our remarks on this subject with a description of experiments performed by M. Gabba in Italy by means of ammonia acting on flowers. M. Gabba simply used a plate, in which he poured a certain quantity of solution of ammonia. He placed on the plate a funnel turned upside down, in the tube of which he arranged the flowers on which he wished to experiment. He then found that under the influence of the ammonia the blue, violet, and purple flowers became a beautiful green, red flowers black, and white yellow, etc.