Note 5 — Chapter XVIII · SILICON AND THE OTHER ELEMENTS OF THE FOURTH GROUP
George Kamensky translation
This alloy, as Beketoff and Cherikoff showed, is easily obtained by directly heating finely divided silica (the experiment may be conducted in a test tube) with magnesium powder (Chapter XIV., Notes 17, 18). The substance formed, when thrown into a solution of hydrochloric acid, evolves spontaneously inflammable and impure silicon hydride, so that the self-inflammability of the gas is easily demonstrated by this means.
In 1850–60 Wöhler and Buff obtained an alloy of silicon and magnesium by the action of sodium on a molten mixture of magnesium chloride, sodium silicofluoride, and sodium chloride. The sodium then simultaneously reduces the silicon and magnesium.
Friedel and Ladenburg subsequently prepared silicon hydride in a pure state, and showed that it is not spontaneously inflammable in air, at the ordinary pressure, but that, like PH3, and like the mixture prepared by the above methods, it easily takes fire in air under a lower pressure or when mixed with hydrogen. They prepared the pure compound in the following manner: Wöhler showed that when dry hydrochloric acid gas is passed through a slightly heated tube containing silicon it forms a very volatile colourless liquid, which fumes strongly in air; this is a mixture of silicon chloride, SiCl4, and silicon chloroform, SiHCl3, which corresponds with ordinary chloroform, CHCl3. This mixture is easily separated by distillation, because silicon chloride boils at 57°, and silicon chloroform at 36°. The formation of the latter will be understood from the equation Si + 3HCl = H2 + SiHCl3. It is an anhydrous inflammable liquid of specific gravity 1·6. It forms a transition product between SiH4 and SiCl4, and may be obtained from silicon hydride by the action of chlorine and SbCl5, and is itself also transformed into silicon chloride by the action of chlorine. Gattermann obtained SiHCl3 by heating the mass obtained after the action (Note 4) of Mg upon SiO2, in a stream of chlorine (with HCl) at about 470°. Friedel and Ladenburg, by acting on anhydrous alcohol with silicon chloroform, obtained an ethereal compound having the composition SiH(OC2H5)3. This ether boils at 136°, and when acted on by sodium disengages silicon hydride, and is converted into ethyl orthosilicate, Si(OC2H5)4, according to the equation 4SiH(OC2H5)3 = SiH4 + 3Si(OC2H5)4 (the sodium seems to be unchanged), which is exactly similar to the decomposition of the lower oxides of phosphorus, with the evolution of phosphuretted hydrogen. If we designate the group C2H5, contained in the silicon ethers by Et, the parallel is found to be exact:
4PHO(OH)2 = PH3 + 3PO(OH)3; 4SiH(OEt)3 = SiH4 + 3Si(OEt)4.