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XLIII. Analysis of a Siliceous Deposit from the hot Volcanic 

 Springs of Taupo, New Zealand. By J. W. Mallet, Ph.D.^ 



THIS substance occurs as a porous but tolerably compact 

 concretion, opake, and of a white colour slightly tinged 

 with yellow, very tough and difficult to break, and intermediate 

 in hardness between felspar and quartz. 



Its specific gravity, taken in small fragments, is 2*031. 



Digested in a cold solution of caustic potash it dissolves almost 

 completely, though with great slowness. 



It was analysed by fusion with carbonate of soda in the usual 

 way, the portion employed being first dried at 212° in order to 

 separate merely hygroscopic moisture. 



By digesting the finely pulverized mineral in boiling water, I 

 found on testing the water with nitrate of silver that some soluble 

 compound of chlorine was present ; and by employing a larger 

 quantity of the siliceous sinter, having separated the chloride of 

 silver and removed the excess of silver by muriatic acid, on eva- 

 poration to dryness the substance in combination with the chlo- 

 rine was found to be sodium. Nothing but chloride of sodium 

 had been dissolved out by the water ; and by testing the solution 

 of the portion thus w^ashed obtained after fusion with an alkali, 

 it appeared that all the chlorine existed as such, and had all 

 been dissolved by the water. 



The results of the analysis were the following • — 



Silica 94-20 



Alumina 1*58 



Peroxide of iron . . '17 



Lime trace 



Chloride of sodium . -85 



Water 3'06 



99-86 

 If we deduct 1*53 per cent, of the silica as having been com- 

 bined with alumina and oxide of iron, the relative proportions of 

 silica and water in the mineral will be — 



Atom. 

 Silica . . 92-67 1-993 



Water . . 3-06 -340 



numbers which closely approximate to the formula 6SiO^, HO. 

 This difi*ers greatly from the composition of siliceous deposits 

 from the Geysers of Iceland, as given by Damour and Forch- 

 hammer, the per-centage of water being about one-half of that 

 indicated by their analyses. 



* Communicated by the Author. 



