SPECTROCHEMICAL ANALYSIS 383 



than ± 5 per cent of the amount determined. In some cases a pre- 

 cision of ± 1-2 per cent has been claimed. 



Having traced briefly the development of spectrochemical analysis, 

 we shall now describe the functions of a modern spectrochemical 

 laboratory and illustrate these functions by examples from the experi- 

 ence of the Bell Telephone Laboratories. At the outset it should be 

 pointed out that this laboratory is confronted with an exceptionally 

 wide variety of samples to be analyzed, due to the large number of 

 materials used in the Bell System. Other spectrochemical labora- 

 tories, generally speaking, place a different emphasis on the various 

 functions to be described. Furthermore, we work in cooperation with 

 a resourceful and skillful analytical laboratory and a well organized 

 microchemical laboratory,^ both of which have developed methods for 

 some materials covering the usual range of the spectrograph. As a 

 result our functions have been limited in some directions but extended 

 in others, so that again our experience may be somewhat different from 

 that of other laboratories. On the other hand, the work of this 

 laboratory illustrates the flexibility of the spectrochemical method by 

 demonstrating that it can sometimes be even more useful in collabora- 

 tion with other methods than in competition with them. 



1. Qualitative Analysis for Metallic Impurities 



This is probably the most common type of service performed. 

 The spectrograph is admirably suited for such analyses since, although 

 it utilizes only a small amount of sample, it can detect almost in- 

 finitesimal quantities of the metals and most of the metalloids. Fur- 

 thermore, a complete qualitative analysis can be run in a few hours — if 

 the spectrum is simple or the sample relatively pure one hour is usually 

 sufficient. Thus in a relatively short time and using only a small 

 portion of a completely unknown specimen a guide can be furnished 

 for quantitative analysis by spectrochemical or other methods. As 

 we shall see in the following section, it is possible also to obtain a fair 

 idea of the quantities of each metal present from the same spectrogram. 



Numerous examples could be cited but it will be sufficient to state 

 that all "general unknowns" are first subjected to a spectrochemical 

 qualitative examination before further analysis is attempted, and to 

 give two typical cases. A silver contact was behaving abnormally in 

 tarnish tests and was submitted for analysis. A qualitative test 

 revealed that the silver contained thallium. Subsequent checks on 

 the spools of silver wire from which contacts had been made showed 



''Clarke and Hermance, "Microchemical and Special Methods of Analysis in 

 Communication Research," Bell Sys. Tech. Jour., 15, 483 (1936). 



