Selenium

“ I think this experiment proves that selenic acid is not injurious to plants when used in small quantity, and that the acid is taken up and retained by plants, or at least by certain varieties of plants. The experiment, however, did not prove whether or not there was a partial replacement of sulphur trioxide by selenium trioxide or of sulphur by selenium. Having lately become possessed of large quantities of selenium compounds, I propose to grow plants in soil or water free from sulphur in any form, but supplied with potassium and ammonia selenates. ”

“ Chem., 1857, 71, p. 279) fuses the commercial selenium with potassium cyanide in a stream of hydrogen, takes up the melt in water and passes air through the solution; the precipitated tellurium is filtered off, and the solution then supersaturated with hydrochloric acid, when selenium is gradually deposited. E. Divers, (Chem. News, 1885, 51, p. 199) dissolves the element in boiling concentrated sulphuric acid and reduces the resulting selenious acid with sulphur dioxide, filters off the precipitate and washes it with water and alcohol. ”

“ We have observed that melted selenium behaves to the other substances as water to a greasy surface, and we are inclined to think that, when selenium is used in connection with metals not chemically acted upon by it, the points of contact between selenium and the metal offer a considerable amount of resistance to the passage of a galvanic current. By using brass we have been enabled to construct a large number of selenium-cells of different forms. The mode of applying the selenium is as follows: The cell is heated, and, when hot enough, a stick of selenium is rubbed over the surface. ”

“ Synthesis of 2-methyl-4-selenoquinalozone, 2-phenylbenzoselenazole and Its Derivatives INTRODUCTION
The general conception of selenium is that it is a comparatively rare element. Few realize that it has been known for over a century and that over twenty selenium minerals, containing from one to sixty-six per cent. of the metal, are considered by the mining corporations as important. ”

“ In turning off the gas light of the city at day break, in controlling the draft of the factory chimneys, and in regulating the rapidity of the manufacture of sulphuric acid, the selenium cell is an important labor saving factor. ”

“ Selenium combines directly with hydrogen when heated in the gas, and with fluorine in the cold. It burns with a blue flame when heated in the air or in oxygen, at the same time giving a characteristic smell of rotten horseradish, a reaction which serves for the recognition of the element. It combines directly with nitrogen, phosphorus, antimony and carbon, and with all the metals (except gold) to form selenides, of which those of the alkali and alkaline earth metals are soluble in water. Metallic selenium is a conductor of electricity, and its conductivity is increased by light ”

“ But if the seleniate of soda be mixed with muriate of ammonia and heated, selenium, nitrogen and water come over, no trace of sulphur appearing. The selenium may, however, be dissolved in excess of nitric acid, and the selenious acid produced tested by [p472] muriate of baryta, which would then separate sulphuric acid if present; the clear solution is to be saturated with carbonate of soda, evaporated to dryness, and the mixture of selenite and nitrate of soda obtained, fuzed in a porcelain crucible over a spirit-lamp. ”

“ The allotropy of selenium was first investigated by Berzelius; and more fully in 1851 by J.W. Hittorf, who carefully investigated the effects produced by heat; crystalline selenium possesses a very striking property, viz. when exposed to the action of light its electric conductivity increases. Another element occurring in allotropic forms is sulphur, of which many forms have been described. E. Mitscherlich was an early worker in this field. A modification known as “black sulphur,” soluble in water, was announced by F.L. Knapp in 1848, and a colloidal modification was described by H. Debus. ”

“ The resistance of selenium undergoes a change under the polarising action of an electric current, the variation increasing with the strength and the duration of the current. The effect of polarisation is however negligible, if the current be feeble and of short duration. There is a possibility of another difficulty arising from the effect of daily variation of temperature on the normal resistance of the selenium cell. Allowance for this could be made by taking a continuous record of the effect of hourly variation of temperature on the resistance of the cell kept in darkness. ”

“ If care is taken to limit the rise of temperature of the selenium to 100° C., and if it is very gradually cooled after being maintained for an hour or two at that temperature, a mass is obtained which conducts electricity to some extent, and which shows increased conductivity under the influence of light. But in examining the conductivity of selenium so prepared at various temperatures below 80°, and without accession of light, it was found that its conductivity increases with rise of temperature, in which respect it resembles carbon, sulphide of metals, and generally electrolytes. ”

“ The receiver consisted of a parabolic reflector to catch the rays [Pg 50] and focus them on a selenium cell connected by an electric circuit with an ordinary telephone earpiece.
On delivering a message into the mouthpiece the speaker would, by agitating the mirror, send a succession of light waves of varying intensity towards the distant selenium cell. Selenium has the peculiar property of offering less resistance to electrical currents when light is thrown upon it than when it is in darkness: and the more intense is the light the less is the obstruction it affords. ”

“ In certain cases, sulphur, selenium, or tellurium may take the place of oxygen, and the corresponding compounds are called respectively sulphur acids or sulphacids, selenium acids, or tellurium acids. When the hydrogen of an acid is replaced by a positive element or radical, a salt is formed, and hence acids are sometimes named as salts of hydrogen; as hydrogen nitrate for nitric acid, hydrogen sulphate for sulphuric acid, etc. In the old chemistry the name acid was applied to the oxides of the negative or nonmetallic elements, now sometimes called anhydrides. ”

“ The discovery of a new law of nature, a new ultimate fact, or one that even temporarily puts on that appearance, is like the discovery of a new element in chemistry. Thus, selenium was hardly discovered by Berzelius in the vitriol works of Fahlun, when it presently made its appearance in the sublimates of Stromboli, and the rare and curious products of the Hungarian mines. ”

“ It crystallizes in colourless needles. Selenasulphuric acid, H2SeSO3, is only known in the form of its salts, which are usually obtained by the action of selenium on solutions of the metallic sulphates, a selenotrithionate being simultaneously produced. The salts are unstable and readily decompose when heated. Selenotrithionic acid, H2SeS2O6, is also obtained in the form of its potassium salt by the action of potassium hydrogen sulphite on a selenosulphate. It is readily decomposed by acids with liberation of sulphur dioxide and selenium. ”

“ The element is usually obtained from the flue dust or chamber deposits of sulphuric-acid works in which a seleniferous pyrites is burned. In this process, the residues are boiled with a dilute sulphuric acid to which nitric acid and potassium chlorate are added in order to transform the element into selenic acid, H2SeO4, which is then reduced to selenious acid, H2SeO3, by boiling with hydrochloric acid, and finally to selenium by sulphur dioxide. ”

“ The liquid rapidly deposits free selenium, owing to the oxidation of the hydrogen selenide retained in solution. Light appears to decompose the triselenide into free selenium and the subselenide B4Se.
Silicon selenide, SiSe3, has likewise been obtained by M. Sabatier by heating crystalline silicon to redness in a current of hydrogen selenide. It presents the appearance of a fused hard metallic mass incapable of volatilization. Water reacts most vigorously with it, producing silicic acid, and liberating hydrogen selenide. ”

“ Hydrogen selenide and telluride are gases like sulphuretted hydrogen, and, like it, are soluble in water, form saline compounds with alkalis, precipitate metallic salts, are obtained by the action of acids on their compounds with metals, &c. Selenium and tellurium, like sulphur, give two normal grades of combination with oxygen, both of an acid character, of which only the forms corresponding to sulphurous anhydride—namely, selenious anhydride, SeO2, and tellurous anhydride, TeO2 [79] —are formed directly. ”

“ It was known that crystalline selenium is a substance peculiarly sensitive to light, for when a ray strikes it an electric current passes far more easily through it than if it were kept in the dark. It therefore occurred to Professor Bell that if a telephone were connected in circuit with the current, and the ray of light falling on the selenium was eclipsed by means of the vibrations of sound, the current would undulate in keeping with the light, and the telephone would emit a corresponding note. ”

“ In its natural state selenium is practically a non-conductor of electricity, its resistance being forty thousand million times greater than copper. Its practical value lies in the property which it possesses, that when in a prepared condition it is capable of varying its electrical resistance according to the amount of light to which it is exposed, the resistance decreasing as the light increases. ”

“ Selēnol′ogy, selenography.—adj. Selēnōtrop′ic, turning to the moon.—ns. Selēnot′ropism, Selēnot′ropy. [Gr. selēnē.]
Selenite, sel′en-īt, n. a transparent and beautiful variety of gypsum: a salt of selenium: a supposed inhabitant of the moon.—adjs. Selenit′ic; Selenitif′erous. [Gr. selēnitēs (lithos, stone) , moon-like—selēnē, the moon.]
Selenites, sel-ē-nī′tez, n.pl. a genus of coleopterous insects.
Selenium, sē-lē′ni-um, n. an element discovered by Berzelius in the refuse of a sulphuric-acid factory in 1817.—n. Sel′ēnate, a compound of selenic acid with a base.—adjs. ”

“ The selenium-cells were then placed in a paraffine bath, and exposed for some' hours to a temperature of 210° Cent., after which they were allowed to cool with extreme slowness. The results obtained with these cells were very extraordinary; in some cases the resistance of the cells when exposed to light was only one fifteenth of their resistance in the dark. ”

“ The demand for the metal is so small that there are half a dozen concerns in the United States either willing to supply gratis any reasonable quantity for research work, or to sell it at cost. In a special report of the National Research Council on selenium (3) , it is estimated that there could be produced annually, without making any material additions to the present plants, not less than 300,000 pounds. ”

“ They take this dust and treat it with acids until they get the pure selenium. Sometimes selenium comes in crystal forms, and again it is combined with various metals for different uses.
"There's one good thing about it. There are several varieties, and I'll try them all before I give up."
"That's the way to talk!" cried Ned. "Never say die! Don't give up the ship, and all that. But, Tom, what you need now is a little fun. You've been poking away at this too long. Come on out on the lake, and have a ride in the motor boat. It will do you good. It will do me good. ”

“ A thorough study of one element of a family makes the study of the other members a much easier task, since so many of the properties and chemical reactions of the elements are similar. Thus, having studied the element sulphur in some detail, it is not necessary to study selenium and tellurium so closely, for most of their properties can be predicted from the relation which they sustain to sulphur. ”

“ All the metals are good conductors, though the resistance of lead is 12 times that of copper or silver, that of iron 6 times, and that of mercury 60 times that of copper. The resistance of all metals increases as their temperature rises.
Selenium in its crystalline state may also be regarded as a conductor, though its resistance is 3.7×1012 times that of a piece of copper of the same dimensions. Its resistance increases as the temperature rises. Selenium in the amorphous form is a good insulator, like sulphur.
Many liquids conduct electricity by electrolysis. ”

“ Sulphur compounds have similar physiological action. It is known that triphenylstibine sulphide, or sulphoform, (C6H5) 3SbS, has a curative effect in skin diseases, as it liberates “nascent” sulphur on the skin. It is equally natural to expect some organic selenium compound which liberates finely divided selenium to exert a remedial influence on animal bodies. The selenoquinazolone prepared in the course of this research and described more fully in another section of the paper, has this prospect. ”

“ The clear benzalaniline was then poured into 160 grams of selenium dust in a pyrex flask on a sand bath, the flask being connected with an air condenser as before. In order to distribute the flame to better advantage over the bath, an air space was made between the Meker burner and the bath by introducing a wire gauze. Hydrogen selenide was evolved freely. Complete reaction took three days. ”

“ The light passes through the positive into the cylinder, and is reflected towards a selenium cell; and as the positive has an almost infinite number of gradations of tone, or degrees of light and shade, the amount of light reaching the cell varies constantly all the time. The selenium therefore alters its resistance, and allows a constantly varying current to pass through it, and so to the transmission line.
At the receiving end is another cylinder having the same rotating and forward movement, and round this is fixed a sensitive photographic film. ”