700 KEPORT— 1900. 



Calcium and strontium silicidea are formed by exactly similar reactions from 

 similar compounds. They are white or bluish- white substances of metallic appear- 

 ance, and also resemble aluminium silicide and silicon somewhat in appearance. 



They possess a distinctly crystalline fracture, shewing plate-like crystals very 

 similar to those seen in the fracture of cast zinc, the crystals being, however, some- 

 what smaller in size. 



They oxidise slowly in the air and more rapidly under the influence of heat, 

 yielding silicon dioxide and the oxide of the alkaline earth metals present. Like 

 the carbides they decompose with water, but yield, instead of acetylene, hydrogen 

 in a pure state, which is evolved without explosion, the following being the 

 reaction : — 



(1) CaSio + 6 H,p = Ca (OH)., + 2 SiO„ + lOH 



(2) BaSi.,' + 6 H,0 = Ba (OH); + 2 SiO," + lOH 



(3) SrSi; + 6 H:0 = Sr (OH); + 2 SiO: + lOH 



The calcium compound dissolves slowly in cold water, but more rapidly in hot 

 water ; the barium compound decomposes rapidly in both cold and hot water. 

 The strontium compound dissolves more rapidly in water than the calcium, but 

 not so rapidly as the barium compound. 



It will be noticed by considering the equations 1, 2 and 3, that all of these 

 compounds evolve large volumes of hydrogen :— 



1 lb. CaSio producing •1041b, or 18-73 cubic ft. hydrogen 

 lib. BaSi', „ -OSllb. or 9-15 „ „ 



1 lb. SrSia" „ -069 lb. or 12-36 „ „ 



at 0° C. and 760 mm. 



Calcium silicide, when treated with dilute acids, either the oxy-acids or the 

 hydrogen acids, gives rise to the formation of a new compound which has the 

 formula Si.jHj and is therefore the silicon analogue of acetylene C.,H., and must be 

 called silico-acetylene since it bears the same relation to silico-methane (silicon 

 hydride) SiH^ as acetylene bears to methane CH4. The reaction being • 



CaSi, + 2 IICl = CaClj + Si,H,, 



Silico-acetylene is a yellow crystalline compound and differs in properties from the 

 compound SiHg which Ogier obtained by sparking SiII_, which was unstable and 

 exploded when subjected to a shock, Si^Ho being stable or non-explosive at 

 ordinary temperatures. 



When treated with 20 per cent, solution of caustic soda or potash, SioHj 

 yields hydrogen according to the following equation : — 



SioH^ + 4 NaOII -n 2 H^O = 2 Na, SiO„ + 1 OH 



Heated in air this compound S'l.Jl^ oxidises rapidly, giving 2 SiOo H.,0, and 

 when heated in a closed tube it breaks down into amorphous silicon and free 

 hydrogen. Strontium silicide when treated with a strong acid does not produce 

 silico-acetylene with the same facility, while the barium compound when so treated 

 produces a mixture of gaseous compounds and free hydrogen. These silicides can 

 be produced at low cost where electric power is cheap, are very powerful reducing 

 agents, and we hope will find large use in the dye industries. Some experiments 

 have been tried on molten steel carrying phosphorus and sulphur, and the requisite 

 quantity of silicide of barium or calcium completely removed these impurities as 

 well as all oxygen present. 



8. Report on the Electrolytic Methods of Quantitative Analysis. 

 See Reports, p. 171. 



