282 SCIENCE PROGRESS. 



reproduced in the preceding- pages ; the simplification, or 

 complication, possible in such formulae may be exemplified 

 by the case of Serpentine ; the structure may here be re- 

 presented in three ways : — 



(i.) s/o >M s 



I x O— H 

 O 



I /O— H 

 Si-O— Mg— OH 

 O— Mg— OH 



(ii.) OH-Mg-O s . Q O-Mg-OH 



H — > | U " | O— H 



O— Mg— 6 



(iii.) H-O Si Q O-Mg-OH 



H— O | u | O— Mg— OH 



O— Mg— O 



The first is that adopted by Brauns, the second is that 

 of Tschermak, but the third expresses perhaps even more 

 suggestively the breaking up of the mineral into Enstatite 

 and Olivine. Tschermak prefers the symmetrical grouping 

 (ii.) as harmonising better with the derivation of Serpentine 

 from two molecules of Olivine. 



Groth suggests that Serpentine may be one of the two 

 following molecular compounds, H 2 Mg 3 (Si 4 ) 2 . H 2 or 

 (Mg OH) 2 Si 2 5 . Mg (OH) 2 , the former representing a chlo- 

 ride mineral with one molecule of water of crystallisation, 

 the latter a molecular compound of Picrosmine and Brucite ; 

 but here we begin to lose sight of the relationship to Olivine 

 which is suggested by the pseudomorphs. 



I have entered at some length into the views which have 

 been propounded concerning the chemical construction of 

 Serpentine as an instance of the arguments used by these 

 able chemists in their endeavours to solve the mystery of 

 the natural silicates. 



Such speculations should perhaps be regarded rather as 

 illustrating the straits to which mineralogists are driven in 

 their study of the silicates than as successful attacks upon 



