What does black blotting paper in the stomach indicate after acid poisoning?

The presence of black blotting paper in the stomach after acid poisoning indicates sulfuric acid (H2SO4) poisoning. This phenomenon occurs due to the corrosive nature of sulfuric acid, which can lead to significant damage to the gastrointestinal tract. When sulfuric acid comes into contact with the tissues in the stomach, it causes a dehydration effect, leading to the formation of carbonized or charred material resembling black blotting paper.

This visual characteristic is specific to sulfuric acid because of its heavy corrosive properties and ability to dehydrate tissues, which is not typically seen with other acids. Hydrochloric acid (HCl) tends to cause erosive lesions without such carbonization, nitric acid (HNO3) creates yellow-brown discoloration due to the formation of methemoglobin, and carbonic acid (as a weak acid) does not produce significant tissue damage, thus not leading to such findings. Hence, the distinct appearance of black blotting paper serves as a diagnostic indicator for sulfuric acid poisoning.