276 Dr. J. E. Reynolds on certain Mineral Silicates. 



Dana, do not appear to contrast favourably as regards simplicity 

 with the older ones, I venture to bring forward some views which 

 I have long held on the symbolic notation for the anhydrous si- 

 licates and on some points in their constitution. These views 

 were expressed in substance at one of the meetings of the Royal 

 Geological Society of Ireland last session; and the present junc- 

 ture seems a favourable one for discussing them and exhibiting 

 some advantages derivable in practice from their application. 



In the following observations it will be understood that the 

 new atomic weights for the elements are those employed, unless 

 otherwise specified. 



It is usual at the present time to represent the silicates as 

 constructed on the type of water ; thus the normal* hydrate of 

 SiO 2 is 



g 4 i() 4 , the type being g!|o 4 . 



A normal silicate is therefore 



t>4 r O 4 ? an( ^ a metasilicate p 2 ^O 3 . 



This, as we all know, is the general plan adopted by modern che- 

 mists for expressing the composition of these salts, variously 

 modified, however, by each author to suit his idea of the mode of 

 representing the constitution of the molecule. Thus Odling or 

 Wurtz would represent Willemite as 



rOZn"" 



2 ? n „}o«; Naquet, Si IV J g 



Frankland, SiZnO 2 "; and Dana, Si||0 4 ||Zn 2 . 



On ordinary grounds there can be no objection to the use of 

 the formulas just given; but practically they all have the very 

 serious defect of hiding the ' ' oxygen ratio " of the compound, 

 and we shall see presently that this defect is exaggerated as 

 we ascend in the series. It is difficult to understand how 

 mineralogists can do without the aid which this ratio affords in 

 the determination of species ; and it appears to me to be of the 

 utmost importance for the interests of practical mineralogy, that 

 any formulas now employed should be capable of exhibiting the 

 above ratio as clearly as those written in the old way did. I 

 am well aware that in order to do this it would appear to be ne- 

 cessary to surrender typical formulas altogether; but it will be 



* In the following pages I have adopted, for the sake of harmony, the 

 nomenclature and order of description of the silicates which Professor Dana 

 employs in the new edition of his ' Mineralogy.' Dana calls the normal 

 salt a unisilicate, and the second compound a bisilicate. 



