[11 bis] The following consideration is very important in explaining the nature of the lower hydrates which are known for silicon. If we suppose water to be taken up from the first hydrates (just as formic acid is CH(OH)_{3}, _minus_ water), we shall obtain the various lower hydrates corresponding with silicon hydride. When ignited they should, like phosphorous and hypophosphorous acids, disengage silicon hydride, and leave a residue of silica behind--_i.e._ of the oxide corresponding to the highest hydrate--just as organic hydrates (for example, formic acid with an alkali) form carbonic anhydride as the highest oxygen compound. Such imperfect hydrates of silicon, or, more correctly speaking, of silicon hydride, were first obtained by Wöhler (1863) and studied by Geuther (1865), and were named after their characteristic colours. (_See_ Note 6). _Leucone_ is a white hydrate of the composition SiH(OH)_{3}. It is obtained by slowly passing the vapour of silicon chloroform into cold water: SiHCl_{3} + 3H_{2}O = SiH(OH)_{3} + 3HCl. But this hydrate, like the corresponding hydrate of phosphorus or carbon, does not remain in this state of hydration, but loses a portion of its water. The carbon hydrate of this nature, CH(OH)_{3}, loses water and forms formic acid, CHO(OH); but the silicon hydrate loses a still greater proportion of water, 2SiH(OH)_{3}, parting with 3H_{2}O, and consequently leaving Si_{2}H_{2}O_{3}. This substance must be an anhydride; all the hydrogen previously in the form of hydroxyl has been disengaged, two remaining hydrogens being left from SiH_{4}. The other similar hydrate is also white, and has the composition Si_{3}H_{2}O (nearly). It may be regarded as the above white hydrate + SiO_{2}. A yellow hydrate, known as _chryseone_ (silicone), is obtained by the action of hydrochloric acid on an alloy of silicon and calcium; its composition is about Si_{6}H_{4}O_{3}. Most probably, however, chryseone has a more complex composition, and stands in the same relation to the hydrate SiH_{2}(OH)_{3} as leucone does to the hydrate SiH(OH)_{3}, because this very simply expresses the transition of the first compound into the second with the loss of water, SiH_{2}(OH)_{3} - H_{2} + H_{2}O = SiH(OH)_{3}. When these lower hydrates are ignited without access of air, they are decomposed into hydrogen, silicon, and silica--that is, it may be supposed that they form silicon hydride (which decomposes into silicon and hydrogen) and silica (just as phosphorous and hypophosphorous acids give phosphoric acid and phosphuretted hydrogen). When ignited in air, they burn, forming silica. They are none of them