This post was written by Trey Smith, the Library of Congress 2015-16 Science Teacher in Residence. This post comes in anticipation of National Chemistry Week.
Throughout history, humans have sought out substances to color, coat, and cover dwellings, objects, and bodies. Modern inorganic pigments and dyes joined natural and organic substances used by the ancients. The properties of one substance, lead white, once made it the pigment of choice in white paint.
Paints are colloids, mixtures that include a pigment, solvent, and binding medium. Lead white was the main white pigment used by classical European artists and for painting building exteriors and interiors. Over time, paints using zinc oxide and titanium dioxide compounds competed with lead paint.
An 1852 article in the New York Daily Tribune describes the toxicity of lead in paint and points to a zinc-based pigment as a desirable alternative. Students might:
- make note of the arguments offered against lead and for paints with zinc;
- be inspired to research the use of zinc oxide and titanium dioxide today and their properties, such as opacity and solubility; and
- apply what they know about elements, compounds, and mixtures to the article.
Despite health concerns about lead, lead remained a prime paint pigment. Students might compare the 1852 article to later articles that promote the continued use of lead paint.
- A 1907 advertisement in The Lafayette (LA) Advertiser tells consumers to stick with white lead paint; and
- A 1918 ad for certain-teed paints and varnishes points to government approval of lead white paint.
A key question for further investigation would likely emerge during the comparison: Why did lead paint remain in use? Ask student to identify tools and techniques the companies used to sell their products. What is scientific about the advertisements? What is not scientific or even pseudoscientific?
The federal government finally banned the use of lead-based paints in the construction of public housing in 1971 and instituted a broader ban in 1978. But the public health concerns and public policy debates about lead did not end. Two decades later, the Senate passed, but the House subsequently rejected, the Lead Exposure Reduction Act of 1994. The bill text presents an argument in Title I (called “findings” in legislative lingo) to describe why Congress is taking further action on lead. Students might:
- dig deeper into the argument presented in the legislation;
- offer their own arguments, after conducting research, for policy action or inaction on lead; and,
- use the legislation as a starting point for problem- and project-based learning, especially since concerns about lead poisoning are intertwined with issues of race and class.
Recent lead legislative text provides a context for learning about scientific measurement. While science classes typically focus on measurement for the purpose of experimentation in a lab, the Consumer Product Safety Improvement Act of 2008 uses measurement language about parts per million (ppm). Instead of telling students about ppm beforehand, allow students to raise their own questions about the term. Students might also investigate further:
- What are related proportions and measurements used to scientifically describe amounts of substances?
- Are there other public policies that use ppm standards?
In each case, the primary sources related to lead poisoning provide opportunities to examine arguments, place science in public contexts to increase student engagement, and catalyze further chemistry learning. What other opportunities emerge from using newspapers and legislative text in a chemistry class?