A study has been made of the transmittance of near infrared energy by a number of binary glasses. Of the systems studied, the lithia-silica and lead oxide-silica were found to have the highest transmittance of cnergy ill the range of wavelengths from 3.0 to 5.0 micron s. Thc' t rallsmittance of lithia-silica is compared with that of 1.he other alkali-silica glasses. Values of transmittance are given for lead silicate glasses of highcr lead eontellt than have been previously reported in the literature.

All curves demonstrate the reproducibility which can be attained with the apparatus.A study has been made of the transmittance of near-infrared energy by a number of binary glasses. Of the systems studied, the lithid-ailica and lead oxide-silica glasses were found to have the highest transmittance of energy in the range of wave lengths from 3.0 to 5.0 microns. The transmittance of lithid-silica glass is compared with that of the other alkali-silica glasses. Values cf transmittance are given for lead silicate glasses of higher lead content than previously reported in the literature.

The infrared transmittance of some calcium aluminate and germanate glasses has b ecn measured out to 6 microns. The range of compositions of the calcium alum inate glasses was CaO , 26.7 to 52 .0 pOl'cent, and A1z03, 28.2 to 49.6 perccnt. Barium oxide, BeO, Bi20 3 • La20 z, MgO, a nd PbO were added in varying amounts up to a maximum of 36.0 percent for anyone constitucnt. These calcium alumi nate glasses are good infrared t ransm itters but show a prominent water absorption band at 2.9 to 3.0 m icrons. This absorption ca~ be decreased somewh at by means of a dry air t reatment of the melt. Thcse glasses have a st rong tendency toward devitrification .Ge rmanium oxide is a good glass-fo rmer. Its glasses have about the same infrared t ransmi ttance as the calcium aluminate glasses in the absence of ox ides such as Si02 and BcO, " ' hich absorb in the '1.5-to 5.5-micron region .

(3] Thermal proper t ies of petrole um produ cts, NBS Misc. Pub . J\I97 (1929 An a nalysis has been made of t he absorpt ion ,bands of v ario us g~asses. by calcula ti?n of t he inte rnal t ransm ittances and surface losses. The waveleni1; t hs,. Ill ~ICrons , assocIated wi th broad a bsorp tio n bands ha ve been m easured , a nd t he a ctIve vIbratll;g grou ps cau smg t he a bsorp tion are a s follows : 2.7, CO2 ; 2.75, OH ; 2.75, CO2; 2. 9, OH asso Cl at~d ; 3.5, C O~--; 3.65, (N 0 3-) ; 3.8, Si -O bond ; 4. 0, C0 3--; 4.15, (N 0 3-) ; 4.25, CO2; 4.45, SI-O b?ncl ; a nd 4.7, OH associated . The g rea tes t lo s~ of infra red e neygy fo r a num be r of glasses IS cau sed by surface losses, rathe r tha n by tr ue m te rnal a b orptlOn.

Most silicate glasses have a region of absorption for radiant energy at wavelengths lon ge r t han 2.7 micron s. This absorption has been found to be cau sed by t he presence of water and CO2 in t he glass. Means for removin g much of this ab~o~ption from. so me glas?es hav~ been d eveloped. Also, it has been found t hat glasse.s contall1ll1g lead oXide or banum oXide, or combinations of the t wo , do not appear to retall1 as IToJuch. ,yater a s m?st o~he r glasse? . A soda-lead oxide-silica glass and a barium oxide-lead oXide-SIlIca glass with hi gh tran smi SSIOn for near-infrared energy have been developed .