136 CARNEGIE INSTITUTION OF WASHINGTON. 



by the leading American manufacturer had been increased from 

 15,000 to 28,000 pounds per month and its quaUty improved to such 

 an extent that rejections by government inspectors became compara- 

 tively rare. The output will probably reach 45,000 pounds gross 

 during the month of October, and if necessary can now be increased 

 still further. 



Now that the output has reached a magnitude such that an adequate 

 supply of suitable glass is assured for national needs, the attitude of 

 this laboratory toward the problem has changed somewhat. Instead 

 of straining every nerve to increase gross production, many refinements 

 are now being effected of a character to bring the quality of the glass 

 to a higher level. Of these a more detailed account will be published 

 in due time. 



Of the quality of the glass now produced, it may be said that the 

 present product is homogeneous and free from optical imperfections 

 except in so far as ''stones" still occasionally interfere to compel 

 wasteful cutting of otherwise excellent blocks. These are due at the 

 moment solely to unsuitable clay melting-pots, granules of which are 

 easily detached and remain in suspension in the glass. It is easy to 

 see that in a charge of optical glass weighing 1,000 pounds or more and 

 requiring to be stirred (as other glasses are not) for several hours to 

 produce the desired homogeneity, the pot wall, always more or less 

 soluble, may contribute grains which can not be eliminated. More- 

 over, glass pots after manufacture require some four months to dry 

 before they can be used, and the pots now in use by the trade were 

 neither developed nor intended for optical glass. An appropriate 

 study of this problem will necessitate improvements in the pot-maker's 

 art which are no less extensive than those which confronted the glass- 

 maker. This phase of the investigation has aheady been actively 

 taken up by Dr. A. V. Bleininger, ceramic chemist of the Bureau of 

 Standards (Pittsburgh), who has given assurance that an early and 

 adequate solution is near. 



The second cliief problem which confronts the glass-maker is the 

 large absorption of Ught in American-made glasses compared with 

 the foreign glasses hitherto available. Without entering upon unnec- 

 essary detail, this has been shown to be due primarily to the iron 

 contained in all the raw materials from which American glasses must 

 be made. In so far as the ingredients of the glass are concerned, 

 this difficulty has already been met through the cooperation of the 

 United States Geological Survey in seeking suitable sources of glass- 

 sand and of chemical manufacturers in purifying their output. There 

 still remains, however, the disagreeable fact that American pot clays 

 show some 2.5 times the iron content of the European pot clays, in 

 consequence of which the solution of as much as 1 millimeter of the 

 pot wall in the melting glass will multiply the iron content of the glass 



