Due to the abnormally high temperatures expected in the city within 24 hours, 240 tanks of kvass were brought in. Five criminals poisoned one of the kvass tanks; they were all caught and sentenced to death... They don't remember which tank they poisoned... Is it possible, by experimenting on the convicted, to identify the poisoned kvass tank, if it is known that even a negligible dose of poison is fatal, and the poison begins to take effect within 12 hours of entering the body?
The answer must be justified. An answer without justification will not be accepted.
Amendment: the poison will definitely kill the convicted person within 12 hours, but it may start to take effect at different times.