412 



Scientific Proceedings, Royal Dublin Society. 



To prepare the mineral for chemical analysis, it was removed 

 from the mother-rock, powdered, and then inserted into a " Thoulet- 

 solution" in order to separate it from all adherent foreign matter. 

 Success attended this process, and the powder was observed under 

 the microscope to be free from all impurities. The specific gravity 

 was determined to be 2*26 at a temperature of 11° C. The ana- 

 lyses were conducted with the usual care, and the purity of the 

 precipitates was tested in all cases. A small quantity of alumina 

 was found to remain with the silica, and an almost equal quantity 

 of silica was detected with the alumina. The difference between 

 these two quantities, 0'08°/ o , had to be deducted from the silica 

 and added to the alumina. The mineral is easily dissolved by 

 acids with gelatinization. The amount of H 2 was estimated 

 three times. 



Under I. is given the mean of my two almost identical ana- 

 lyses. 



Under II. a natrolite-analysis made by Thomson, the locality 

 being given as "Antrim". He states that the mineral was "full 

 of holes, through which water containing iron seems to have 

 filtered." 1 



Si0 2 



A1 2 3 



FeO 



CaO 



Na 2 



K 2 



H 2 



Sp. g. = 



100-02 101-33 



2-26 Sp. g. = 2-139 



Divided by the atomic weights of the substances, my analysis 

 would give — 



0-776 

 0-27 

 0-046 

 0-214 



0-562 



or 



7-76 



2-7 



0-46 



2-14 



5-62 



Si0 2 

 A1 2 3 

 CaO | 

 Na 2 j 

 H 2 



2-60 



= 3 



= 1 



Na 2 = 1 



= 2-16 



I. c vol., i., p. 317. 



