HIGH-GRADE SILICA MATERIALS 25 



than 0.002 per cent Fe 2 O 3 ; for the better grades of lead flint, used 

 in the manufacture of cut glassware, the percentage of iron oxide 

 should not exceed 0.02 per cent. 



Plate glass used for mirrors may be made from sand containing 

 as much as o.io per cent Fe 2 O 3 , while if the plate glass is to be used 

 for windows the amount of iron oxide in the sand may run as high 

 as 0.20 per cent; in the case of ordinary green and brown bottle 

 glass, sands may be used containing from 0.50 to as high as 7 per 

 cent ferric oxide. 



Provided quartz rock is used instead of sand, the rock should 

 break down readily into a fine granular sand of fairly uniform grain, 

 when crushed ; this will be the case provided induration has not pro- 

 ceeded far enough to have converted the rock into a hard compact 

 quartzite with more or less intricately interlocking structure. 



The formations which seem most nearly to meet the foregoing 

 requirements are (a) the white saccharoidal variety of the Potsdam 

 sandstone, near Johnstown, and in the Moira-Bangor-Mooers dis- 

 trict; (b) the Oriskany sandstone at Oriskany Falls, and (c) the 

 Oneida glass sand. 



Structurally both the Potsdam and Oriskany meet the conditions, 

 breaking down without much difficulty into grains not far removed 

 in size from the rounded originals of which the rocks were made. 



The results of sieve tests on the crushed, washed and dried rock, 

 and on the Oneida glass sand, are given in table 3. The grains are, 

 moreover, fairly angular, because even in the friable saccharoidal 

 sandstones the grains have been more or less affected by secondary 

 growth, which has been sufficient to give them angularity of form 

 without at the same time having developed a very firmly interlocking 

 structure. 



Some of this material seems to meet the requirements with respect 

 to composition also, judging from the results of the analyses; by 

 referring to tables i and 2 it will be seen that the better beds of the 

 Potsdam in both the Johnstown and Moira-Bangor sections contain 

 very promising material for glass making, as does also the Oriskany 

 sandstone. 



Washing seems to improve the crushed rock to some degree, and 

 it might even be possible to obtain from some of the beds rock 

 which, after proper treatment, would closely approach optical 

 quality. There has been included in table I an analysis of Oriskany 

 sandstone from Pennsylvania, for the purpose of comparison ; this 

 sandstone, under favorable conditions of weathering, disaggregates 



