A Rapid Visual Test for the Quantitative Determination of 

 Small Concentrations of Calcium in Lead* 



By EARLE E. SCHUMACHER and G. M. BOUTON 



A method is described for estimating calcium in lead which consists in 

 casting a test ingot in a prescribed manner and comparing its surface 

 appearance with the surface appearance of standards. The calcium 

 content can be determined by inspection. 



IN THE manufacture of lead-calcium sheath it is desirable to control 

 the calcium content to 0.028 ± .005 per cent in order to obtain the most 

 desirable combination of properties. Since calcium is a very active element 

 chemically, special manufacturing procedures were developed to minimize 

 the contact of molten lead-calcium alloy with the air. Despite the im- 

 proved techniques, some calcium is always lost and must be replaced. 

 Before this can be accomplished satisfactorily, obviously, the calcium con- 

 tent of the alloy must be determined. Conventional chemical procedures 

 are accurate but not entirely satisfactory for plant control use because they 

 are time consuming and too costly. The best of the chemical methods 

 introduces a lag of at least two hours in melting kettle control. Quantita- 

 tive spectrographic analysis methods were carefully tested, and while 

 they showed some advantage over conventional methods, they were still 

 unduly time consuming. 



With the ever increasing interest in lead-calcium alloys for cable sheath, 

 storage-battery grids, and other applications, it became desirable that a 

 rapid, reliable and not too costly method be developed for determining their 

 calcium content. In approaching the problem, several methods of attack 

 involving physical, chemical, or electrical properties suggested themselves. 

 A few of the methods investigated were: 



1. Observations of the rate of oxidation or tarnish of freshly cut surfaces 

 using a variety of atmospheres and temperatures. 



2. Thermal EMF measurements against pure lead. 



3. Measurements of hardness or strength of samples after various heat 

 treatments. 



4. ]Measurements of electrode potentials in various solutions. 



5. Use of various metallographic techniques. 



6. Observation of recrystallization tendencies after the samples had been 

 deformed. 



* This article is being published in Metals and Alloys. 



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