Speedle: Crisis averted.
Horatio: Tell that to his widow.

Using a Draeger Tube to test for nitric acid fumes, the instrument made a clicking sound. This device does not click. The bellows pump is squeezed drawing air through the tube. A reaction takes place between the air contaminant and the material in the tube causing a color change. The length of stain is proportional to the concentration.

Nitric acid is a liquid and not a gas. The gaseous precursor is NO2 when combines with water forms nitric acid, HNO3. Neither causes instant death.

Horatio writes the symbols for sulfuric acid, H2SO4, on a clear board. Both numbers should be in subscript but he writes the 4 as a large number, suggesting a lack of basic chemistry knowledge.