Dr. Heddle and Mr. R. P. Greg on British Pectolites. 251 



from the Morne Mountains, said to be this mineral, have by our 

 own analysis proved to be table spar, and consequently the only 

 locality we have as yet of this mineral in the British Islands. 



Frankenheim argues that pectolite is anhydrous, chiefly because 

 he wishes to prove it to be a hornblende. This is quite inadmis- 

 sible ; from not one locality has it been found anhydrous, and 

 the per-centages from the different localities do not vary much, 

 averaging about 3 per cent. ; and although the proportion of 

 water does vary half a per cent, when the powdered mineral 

 has been dried at 212°, yet when this necessary precaution 

 has been taken, the proportion is in each specimen invari- 

 ably the same ; any previous variation must therefore have been 

 due to hygrometric moisture. In addition to this, we find 

 the mineral to be very slightly absorbent; that from Ratho 

 absorbs *53 per cent, of moisture, that from the Castle Rock 

 •29 per cent., and that from Ayrshire *35 per cent. ; again, it 

 parts with the water it does contain only after the most intense 

 heating. The Castle Rock mineral, after about ten minutes' 

 exposure to a red heat, gave only 1*2 per cent, of water; a loss 

 in the analysis led us to redetermine the water, when, after 

 exposing the mineral to a heat approaching to whiteness for thirty 

 minutes, we got 3'13 per cent. Seeing, then, that the mineral 

 in powder is almost now-absorbent, and that it retains the water 

 it does contain with such tenacity, it appears to us to be an ex- 

 traordinary conclusion to arrive at to say that water is unessen- 

 tial ; and to exclude a constantly present constituent merely to 

 suit a theory, is absurd. 



There is a difference of opinion with regard to the formula of 

 this mineral, and its place in the system. Dr. Scott rejects the 

 formula given by Berzelius, and prefers one of his own, which 

 agrees admirably with his analysis ; but as the quantity of water 

 as therein stated is much greater than elsewhere found, his for- 

 mula of course does not suit the analyses of others. 



Frankenheim also rejects Berzelius's formula, and offers 

 instead, — 



4(4CaO, 3Si0 3 ) + (4NaO, 3Si0 3 )+5HO, 



the calculated per-centages of which are, — 



Silica 15 atoms = 52*76 

 Lime 16 atoms = 34-29 

 Soda 4 atoms = 9'53 

 Water 5 atoms = 3-42 



This, it must be allowed, agrees well with the analytical results; 

 but the question is, does it agree more closely than Berzelius's; 

 for Frankenheim substituted this formula in order that he might, 

 by writing it more simply 4(CaO, NaO) 3SiO y + 110 (where the 



