MM. Buff and Wohler on new Silicon Compounds. 457 



alter the relation between the chlorine and the silicon. But the 

 deportment of the body to aluminium showed the true state of the 

 case. When the vapour of the protochloride is passed over fusing 

 aluminium, it is decomposed with the greatest ease, a quantity 

 of hydrogen is liberated, chloride of aluminium sublimes^ and the 

 rest of the aluminium is covered with a crust of black crystalline 

 silicon. From the composition of the protochloride as finally 

 adopted, it is clear why it is not formed when ordinary chloride 

 of silicon is passed over heated silicon. 



Hydrobromate ofProtobromide of Silicon, Si^Br^ + 2HBr. — This 

 is formed under similar circumstances, and has similar proper- 

 ties to the protochloride. 



Hydriodate of Protiodide of Silicon, Si^P + 2HI is formed in 

 the same manner as the foregoing compounds. It is a dark-red 

 brittle mass, which fumes strongly in the air, is readily fusible, 

 and solidifies on cooling to a crystalline mass. Heated more 

 strongly it boils and distils over. It is only slowly decomposed 

 by water. It is soluble in bisulphide of carbon, with a blood- 

 red colour, and may be obtained in dark-red crystals on concen- 

 trating and cooling the solution. 



Hydrated Oxide of Silicon, Si'-^0^ + 2H0. — This is formed by 

 decomposing any of the preceding compounds by water, but it is 

 easiest obtained as a bye product in the preparation of the proto- 

 chloride. 



After filtering off from the water it is washed with a little cold 

 water, and dried at first by pressing between blotting-paper and 

 then over sulphuric acid. 



Thus prepared it forms a snow-white, light, amorphous pow- 

 der. It is dissolved by caustic and carbonated alkalies, and even 

 by ammonia, with violent disengagement of hydrogen. It can 

 be heated to 300° C. without losing water, and without being 

 changed, but at a higher temperature it takes fire and burns with 

 a phosphorescent light, hydrogen being liberated, which inflames 

 with a violent explosion. 



It burns in oxygen with a brilliant light; it also burns when 

 heated in a covered crucible, but the residual silica is more or 

 less brown from amorphous silicon. In fact, the hydrate when 

 heated gives off siliciuretted hydrogen, though unfortunately only 

 at a temperature at which the latter is decomposed. When the 

 hydrate is heated in a tube, a gas is disengaged which fumes in 

 the air, but on account of the admixed hydrogen does not sponta- 

 neously inflame. When inflamed, however, it burns, formingsilica. 



The hydrate is slightly soluble in water ; and the sohition of 

 it, obtained in the preparation of the protochloride, being filled 

 with bubbles of hydrogen, has all the appearance of being in a 

 state of fermentation. 



The solution of the hydrate has a powerful reducing action, 

 Phil. May. S. 4. Vol. 15. No. 102. June 1858. 2 H 



