Transmission measurements with the Beckman quartz spectrophotometer

The Beekman quartz photoeleetri c sp ectroph otcmeter , covering th e wavelength ra nge from a bout 200 to 1,200 m illi microns, is proving of great utility in swctral t ransm ission and absorption m e asurem en ts. Esse n! ia l features of the instrument are described, including a constant-temperature enc losu re (for samples) designed a nd con structed at the Bureau. Varioll s instrumental characteri stics a re noted an d possible errors di scllssed , particularl y those that may be p re ent in the m eas urement of p olarizi ng samp les. Wavelength calibrations a re shown for two i nstruments. A de tailed ove r-all chec k of t he re li ability of data obtai ned on t he Beckman spect rop hotome ter by m eans of g las stand a rds of spectral transmittance shows it to giv e res ults ove r th e wavele ngth r a nge from 390 to 750 millimicrons fu ll y as reli able a s those obtain ed with othe r spectrophotom et ers, if indi cated precauti ons are taken.