With respect to measuring thirst, an analog scale was used. The boys marked an "X" on a line (14 cm), with 0 cm representing "Not Thirsty", and 14 cm representing "Thirsty". The location of their "X" was then converted to a percentage.
Your third question is an excellent one as it was crucial that the boys could not detect a difference in taste among the three beverages. An independent laboratory used artificial sweeteners to mask the saltiness of the NaCl beverage. A taste test was conducted with several children and adults prior to beginning the study, and statistical analysis revealed that, as a group, they could no detect a difference in taste among the beverages. This same taste test was then administered to each subject at the first visit, and once again, there were no significant differences. There was, however, a tendency for the boys to give the NaCl beverage a lower rating than the other two beverages.