Show DEFIES HEAT AND COLD A new binl tit llis by ric the new aerman glass is a new and singular t arture in that line disregarding us it does the ordinary principle that glassi mu it contain together iv ith silica and a divalent or trivalent metallic oxide the oxide of a metal an alkali metal or but while thus free from alkali can be worked before the blowpipe and has a camall coefficient of expansion pan sion the inventor hays the new york sun was led to the production of his compound glass by studying the state of strain in ordinary glass vessels and tubes cooled in contact with air As a hollow glass g lass vessel cooled in contact with the air has its outer skin in a state of compression while the inside i in a state of tension it is easily dam aged on the inside but is resistant resi stent on he outside a hollow glass vessel if introduced when cold into warm air has its outer skin thrown into a state of compression but it when it ia hot it is exposed to cold air its outer skin is thrown into a state of tension this being the reason why cold air causes glass to crack more readily than liot air docs the inventor succeeded in throwing the outer layer into a permanent state of compression by covering the glass vessel with a thin outer layer of w aich has a small coefficient of expansion the flacks flasks made of such glass can be filled with boiling aniline and immediately sprinkled on the outside with cold water glass dishes too can be heated over the naked flame without cracking bure tubes of this compound glass are also made to meet all the requirements of practice and have been kept in continuous use on locomotives for five months |