CLAYS OF MIDDLESEX COUNTY. 469 



Analyses of so-called Feldspar. 



123 



Free silica, 58.89 57.41 1 



Combined silica (SiO,), 16.99 16.59} 77 ' 4 ° 



Alumina (A1»0 3 ), 18.95 17-55 16.07 



Ferric oxide (Fe^Os), 0.49 0.54 0.53 



Lime ( CaO) , .... .... .... 



Magnesia (MgO), 0.25 



Potash (K2O), 0.15 0.12 0.15 



Soda (Na^O), 0.21 0.21 .... 



Titanic oxide (Ti0 2 ) , with SiO^ 0.90 with Si0 2 



Water (H«0), 4.90 6.30 4.30 



i. Feldspar from the Forbes farm. 



2. Edgar Brothers' feldspar. 



3. Feldspar bank on farm of Knickerbocker Life Insurance 

 Company. 



The analyses show great uniformity in the composition of the 

 material, and while the fluxes are low, still there is considerable 

 sand present, so that high refractoriness would not be looked for. 

 In fact, were it not for the large size of the quartz grains, the ma- 

 terial would fuse at a lower cone than it does. When tested at 

 cone 33 it can no longer hold its shape, although the quartz peb- 

 bles remain intact. A second grade became viscous at cone 31. 

 Since there are also layers or streaks of quartz sand which are in- 

 terbedded with the "feldspar," it is necessary in mining to keep 

 the sand separate from the "feldspar," and divide the latter into 

 twoi or even three different grades. The sand is used either for 

 fire mortar or building purposes, depending on its quality, and 

 the feldspar is used in the fire-brick mixture. 



FIRE SANDS. 



The general relation of the fire sands to- the clay beds of this 

 area has been described in Chapter VIII. 



The fire sand which underlies the Woodbridge fire clay is dug 

 at a number of points in this district, and is used to some extent 

 in fire-brick manufacture, but the use is decreasing. The material 

 is generally a white quartzose sand, with occasional layers of fine 



