OPTICAL GLASS FOR WAR NEEDS 117 



diameter and height and hold 1,000 pounds of crown, and 1,500 

 pounds or more of dense flint. Pots sometimes contribute 0.02 

 to 0.04 per cent, of iron oxide to the glass, which is very 

 objectionable. Again, if a high refractory clay with poor bond- 

 ing qualities is mixed with a better bonding clay, the latter may 

 dissolve out, causing stones to be cast into the glass. The puri- 

 fication of pots after building has been attempted, but it makes 

 the pot porous and entirely too fragile. The outcome of 

 Bleininger's work was a so-called porcelain type of pot, made 

 up of white ware bisque, crushed to pass a ten-mesh sieve, 35 

 per cent. ; pot shell crushed to pass a ten-mesh sieve, 10 per 

 cent. ; feldspar, 3 per cent. ; flint, 4 per cent. ; Tennessee ball 

 clay, Number 5, 15 per cent.; Illinois bond clay, 5 per cent.; 

 and kaolin, 28 per cent. These pots were made by hand and a 

 typical formula for a cast pot is : whitevvare bisque, 48 per cent. ; 

 plastic bond clay, 23 per cent. ; kaolin, 24 per cent. ; feldspar, 5 

 per cent. 



These pots withstand the severe corrosive action of even 

 dense barium crown glass, and are ready for use in much less 

 time than the German type of pot. Just as the glass-makers 

 did all they could to produce a sufficient quantity of good glass, 

 so the pot-makers continued their researches and contributed 

 largely to the final success. La Clede-Christy, the Buckeye, the 

 Gill, and the Willetts Clay Products Companies deserve great 

 credit, while the work on pots is probably considered the 

 greatest contribution of the Bureau of Standards to the glass 

 problem. 



In furnace operations the cycle has been shortened from the 

 two and a half days here fore used customarily to twenty-four 

 hours, a very important improvement in glass-house practice 

 which was worked out by the Geophysical Laboratory in the 

 plant of the Spencer Lens Company. This has been accom- 

 plished by improvements in methods of stirring, stirring 

 machines having almost eliminated the hand stirring which 

 Jena had considered indispensable. Proper stirring is perhaps 

 the most dfficult part of glass-making technique and involves 



