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Rowland's own observations, although, of course, most of them have been given by others: Elements in the Sun, arranged according to Intensity and the Number of Lines in the Solar Spectrum. Not in Solar Spectrum. Antimony, arsenic, bismuth, boron, nitrogen, cæsium, gold, indium, mercury, phosphorus, rubidium, selenium, sulphur, thallium, praseodymium. With respect to these tables, Prof.
Running his finger along the eleventh, horizontal series, he continued: "The gold series not the group reads gold, mercury, thallium, lead, bismuth, and other elements known only to myself.
Sir William Crookes, of course, is best known as a great chemist, discoverer of the element thallium, and inventor of numerous scientific instruments; while Sir Oliver Lodge's most striking work has been in electricity, and more particularly in the direction of improving wireless telegraphy.
Light of one degree of refrangibility that corresponding to this particular green is emitted by the thallium-vapour. We will now remove the thallium and put a bit of silver in its place. The are of silver is not to be distinguished from that of thallium; it is not only green, but the same shade of green. Are they then alike? Prismatic analysis enables us to answer the question.
After waiting a little, we see that the green of the thallium lies midway between the two greens of the silver. Hence this similarity of colour. But why have we to 'wait a little' before we see this effect? The thallium band at first almost masks the silver bands by its superior brightness.
"Thallium!" I exclaimed, astonished in my turn. "Yes," responded Gazen, hurriedly. "Make a note of the observation, and also of the time. You will find a book for the purpose lying on the desk." I did as directed, and awaited further orders. The silence was so great that I could plainly hear the ticking of my watch laid on the desk before me. At the end of several minutes the professor cried
But the contemplation of the facts will render this subject more intelligible than words can make it. Within the camera is now placed a cylinder of carbon hollowed out at the top; in the hollow is placed a fragment of the metal thallium. Down upon this we bring the upper carbon-point, and then separate the one from the other.
Crookes, pursuing the same method, discovered the bright green band of Thallium, and obtained the salts of the metal which yielded it. The metal itself was first isolated in ingots by M. Lamy, a French chemist. All this relates to chemical discovery upon earth, where the materials are in our own hands.
Thus the kind of metals which formed the sparking points could be determined by analysing the light of the spark. This suggestion has been of great service in spectrum analysis, and as applied by Bunsen, Kirchoff, and others, has led to the discovery of several new elements, such as rubidium and thallium, as well as increasing our knowledge of the heavenly bodies.
These objections do not lie against the thallium paper, the oxidation to brown oxide by either ozone or hydrogen peroxide not requiring the presence of moisture, and the color, therefore, being independent of the hygrometric state of the air. Moreover, when well cared for, the papers undergo no farther change of color and may be preserved indefinitely.
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