The Two-Color Formaldehyde Clock

Aiiodier day. - The rich dark green of the tulip-trees and the oaks, the grey of the swamp willows, the dull hues of the sycamores and black-walnuts, the emerald oj the cedars (after rain) and the light yellow of the beeches. 

Formaldehyde is toxic. The experiment should be carried out in well-ventilated hood. 

SOO-ml. beakers, four 250-mL graduated beakers, dropping pipettes, stock bottles for indicator solutions, two 1-L measuring cyclinders, safety glasses, proiective gloves. 

Formalin (formaldehyde solution, 37%), sodium sulfite, sodium hydrogen sulfite, ethylencdiamine tetraacetate (EDTA), thymolphthalein solution, p-nitrophenol, phenolplulialein, elhaiiol. 

Solution A 22 mL of formaldehyde solution are diluted to 1 liter with water and allowed to stand for 24 h to allow complete depulynierlsailon lo occur. The HCHO concentration is 0.3 mol/L. 

---