349 



on which day there was least moisture in the air, is the mean 

 of the whole three observations. 



Sir Robert Kane brought under the notice of the Aca- 

 demy the results of the analysis of the waters of the streams 

 which descend from the side of the Dublin mountains, such 

 as the Three Rock Mountain, with a view to illustrate the 

 process of decomposition of the granite masses of those rocks, 

 and the conversion of the felspathic elements into clays adapted 

 for ceramic manufactures. A great number of springs and 

 wells along the line of hills from Glencullen to Dundrum had 

 been examined, and with similar results ; but Sir Robert Kane 

 specially detailed the quantitative analyses of two waters from 

 Ticknock, above Rathfarnham, on the flank of the Three Rock 

 Mountain. 



The first of these specimens of water was taken from a 

 rapidly running stream, and it was found that it contained a 

 considerable quantity of soluble silica, combined with alkalies, 

 there being both potash and soda present. This stream passed 

 over a considerable tract of decomposing granite : 148,000 

 grains of this water left a residue on evaporation of 12-5 grains. 

 This residue was found to contain the ordinary constituents of 

 surface water, but in addition, alkalies and silicates amount- 

 ing to — 



Silica, 5,061 } 



Potash, 2,345 C 100,000. 



Soda, • 13,950 J 



The presence of alkaline silicates in such quantity in this 

 water induced Sir Robert Kane to have a still more detailed 

 analysis made of the water contained in a cavern excavated in 

 one of the quarries made for obtaining what is called freestone, 

 that is, the coarse powder of decomposed granite used in Dub- 

 lin for scrubbing floors. This water was stagnant, and was de- 

 rived from drainage through the adjoining masses of decompos- 



