TEST FOR DETERMINATION OF CALCIUM IN LEAD 435 



Unfortunately, none of these methods proved adequate. Either the 

 properties involved were insufiliciently sensitive to changes in calcium con- 

 tent, or other factors masked the effect of calcium. 



Early in the study of lead-calcium it was noticed that the molten alloys 

 quickly filmed^over with oxide. Careful observation of the characteristics 

 of these molten alloys revealed no phenomena that varied sufficiently with 

 calcium content to serve as a clue to the composition. However, when 

 these alloys were chill cast with as little agitation as possible, the surface 

 of the ingots became progressively duller with increasing calcium content 

 to a certain value. Further increase in calcium content resulted in the 

 Assuring of the surface oxide leaving bright metallic areas exposed. This 

 hssuring phenomenon, which is illustrated in Fig. 1, is the type of composi- 

 tion-sensitive indicator desired. When samples of lead-calcium are melted 

 and cast under controlled conditions the surface markings are reproduced 

 with considerable fidelity in respect to areas of dull and bright surface. The 

 ratio of these areas is dependent on the calcium content. For clearness 

 of illustration the samples were photographed under lighting conditions 

 that made the bright highly reflecting surfaces appear dark in the photo- 

 graph. 



The success of the method is dependent to a large extent on the details of 

 procedure that are given below. Since calcium is readily removed from 

 lead by oxidation, a melting and casting procedure for the test specimens 

 was adopted that resulted in a minimum loss of calcium. Fluxes and inert 

 atmospheres, which normally provide adequate protection against oxida- 

 tion, could not be used here since they seriously interfere with the Assuring 

 phenomenon that is the basis of the method. The means finally adopted 

 consists in melting a strip of the cable sheath to be tested in a hemispherical 

 sheet iron crucible about two inches in diameter. A Bunsen burner flame 

 of sufficient intensity to melt a 100-gram sample in about two minutes is 

 applied to the bottom of the crucible. The bottom edge of the sample 

 melts first and the balance of the sample shdes smoothly into the pool of 

 metal first formed with a minimum of rupture of the surface. The broad 

 round shape of the crucible permits it to be tilted until the lip is but a frac- 

 tion of an inch from the surface of the mold before the metal starts to pour, 

 thus subjecting the stream of molten alloy to only a brief exposure 

 to the atmosphere during pouring. The molten alloy should never be 

 stirred nor should the crucible be shaken unnecessarily during the casting 

 operation. Under the melting conditions described, the casting tempera- 

 ture of the melt is controlled sufficiently if the crucible is removed from the 

 flame three or four seconds after the last portion of the sample has melted. 

 By slight modifications in technique, samples for analysis may be taken 

 directly from the commercial melting kettles. The mold used is probably 



