THE IMPORTANCE OF "IMPURITIES" AND TRACE SUBSTANCES G7 



Condenser Tubes: Traces of arsenic in copper facilitate rolling 

 and greatly reduce corrosion. 



Electro-plating: Tiny amounts of "addition agents" in the bath 

 may greatly improve the nature of the deposited metal. 



Baking: "Arkady" flour (named after Professor Robert Kennedy 

 Duncan) was mainly calcium sulfate, to aid yeast growth. 

 Sodium bromate, a "yeast food", enables bakers to start with 

 much less yeast, the total savings running into millions of 

 dollars annually. 



Lead: Tellurium (about 0.05 per cent) increases corrosion resist- 

 ance and establishes "work-hardening." Barium (0.08 per 

 cent) makes lead ring like a bell. Calcium (0.03 per cent) 

 increases tensile strength, valuable in sheathing cables. 



Brewing: Traces of proteolytic enzymes prevent "cold-cloud" in 

 beer. Water may be "Burtonized" (like that of the River 

 Trent") by traces of lime salts. 



Copper: Traces of copper (e.g., from preserving kettles) inhibit 

 the growth of molds in preserves; also the undesirable growth 

 of algae, etc., in reservoirs. 



Cast Iron: Tellurium is a powerful carbide stabilizer; 0.0005 per 

 cent is added in making chilled car-wheels. 

 Technical DDT, the insecticide, contains some substance or 



substances effective in inhibiting the catalytic release of hydro- 

 chloric acid by some insoluble impurity, possibly iron oxide. 6 

 On the other hand, here are some cases where traces are 



harmful: 



Troublesome Traces 



Foods: Less than one part of copper per million in coffee can be 



tasted. 

 Breiuing: Minute traces of iron make "ink" with the tannin of the 



hops, and in high dilution this gives some beers a sickly 



greenish hue. 

 Soap: Coconut oil containing one part per million of sulfur gives 



a soap prone to rancidity. 

 Lead-burning: Traces of arsenic in an oxy-hydrogen flame prevent 



good welds. Traces of platinum in lead storage batteries 



cause self-discharge. 

 White lead: Traces of silver produce a pinkish discoloration; 



traces of copper, a greenish tone. Over 0.0015 per cent is 



objectionable. 



