SPECTROSCOPY IN INDUSTRY HARRISON 205 



American public with the scientific methods used in his factory, 

 by printing in some of the leading weeklies full-page advertise- 

 ments which pictured a laboratory worker gazing at a spectrogram, 

 with the caption "Eyes That See Through Steel." The description 

 which followed of the value of the spectroscope in perfecting auto- 

 mobile parts was a very good one, but every line in the spectrum 

 at which the man was looking quite obviously had come from zinc 

 atoms ! 



Spectroscopic analysis indicates that no entirely pure sample of 

 any metal has ever been prepared, and since single foreign atoms 

 placed here and there in the lattice structure of a metallic crystal 

 can greatly affect its properties, really pure metals probably have 

 properties with which we are as yet not familiar. 



In the food-preserving industries the spectrograph is coming into 

 very wide application. That 2 or 3 parts of aluminum or lead can 

 be detected readily in 10 million parts of lobster or condensed milk 

 may seem unimportant, since such concentrations are below the toxic 

 limits considered dangerous to health, yet obviously tests on the 

 rapidity with which the internal coatings of cans dissolve in foods 

 stored within them can be made more easily and quickly when such 

 sensitive methods of detection are available. Chocolate and chew- 

 ing-gum manufacturers use spectroscopic analysis to insure that the 

 lead content of their products is below the limits set by pure-food 

 laws. Whiskey distillers, finding something in their product which 

 causes it to turn cloudy, have used the spectrograph to locate the 

 cause in minute amounts of cadmium, let us say (to cloak the real 

 offender in anonymity) ; and by analyzing samples from various 

 parts of the distillery line, have been enabled to locate the coil or 

 condenser which introduced the offending element. 



Has the arsenic and lead been properly removed from sprayed 

 fruits before canning? The spectrograph will tell. Is beer kept 

 in cans dissolving anything more from the container than it would 

 if kept in bottles? Again, the spectrograph gives an easy means 

 of deciding. 



Spectroscopic analyses can be performed by two entirely indepedent 

 and dissimilar means, which have different applications. In emis- 

 sion analysis, use is made of the characteristic light emitted when 

 the material is burned electrically in front of the slit of a spectro- 

 graph. In the second method, absorption spectrophotometry, light 

 waves of every length in the desired region are sent through the 

 material to be analyzed (which must be somewhat transparent, like 

 glass or blood serum or peppermint extract or beer) and the spectro- 

 graph is used to determine how much of the light of each wave 

 length has been absorbed by the material. 



