Q. Will a cement floor for a cellar allow ground-air to pass through it, bringing in contagion in case the soil is polluted, as it must be in Baltimore, judging from a recent letter in your paper?

A. Ordinary hydraulic cement, as commonly applied upon cellar-floors, has too much sand mixed with it to stop the passage of air. In fact, it is difficult to make a cellar-floor air-tight without an application of asphaltum, or other similar substance, applied hot.