. The Bell System technical journal . ing the sensitive range of themethod to the median calcium content desired. Alloys having calciumcontents outside the range of the method may be estimated by admixturewith known amounts of lead-calcium alloys of known calcium lead, in general, cannot be used for dilution because the oxide andpossibly traces of impurities present in it cause the loss of some calciumfrom the mixture. To date most experience with the use of the visual test for calcium hasbeen on alloys made with chemical lead. This grade of lead is substantiallyfree from As, Sn,
. The Bell System technical journal . ing the sensitive range of themethod to the median calcium content desired. Alloys having calciumcontents outside the range of the method may be estimated by admixturewith known amounts of lead-calcium alloys of known calcium lead, in general, cannot be used for dilution because the oxide andpossibly traces of impurities present in it cause the loss of some calciumfrom the mixture. To date most experience with the use of the visual test for calcium hasbeen on alloys made with chemical lead. This grade of lead is substantiallyfree from As, Sn, Bi, Fe, Sb and Zn, and contains about per cent Ni, per cent Cu and per cent Ag. The variation in concentration ofthese elements in the commercial supply has not been found to be greatenough to cause serious interference with the indications given by thecasting test. However, the method is influenced by certain variations inimpurity content which are in excess of those normally encountered in the CO2 REMOVER HUMIDIFIER. H2O OR SALTSOLUTIONPOTASSIUMHYDROXIDE RELEASEVALVE DEWARFLASK TO CASTINGCHAMBER SOLIDCO2 Fig. 3—Apparatus used for regulating atmosphere composition usual supply. The presence of tin in the order of a few thousandths of oneper cent causes low indications of calcium content. The use of high puritylead in place of chemical lead has a similar effect. Bismuth additionsup to per cent are inconsequential. Arsenic and antimony form com-pounds with calcium which dross off in the mixing kettle so that theseelements would not be found in the finished sheath. The effects of theinterfering impurities referred to above can be corrected for, when theirpresence is known, by varying the atmosphere in the casting chamber or byadmixture with a known proportion of alloy having a pre-determinedhigher calcium content. By these procedures fissuring can be made tooccur in alloys that otherwise do not give this manifestation. In practicaloperation the brand of lead
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
