about 11 o'clock
The day of our ascension was that of the great fair of September , which attracts all the world to Frankfort . The apparatus for filling was composed of six hogsheads arranged around a large vat , hermetically sealed . The hydrogen gas , evolved by the contact of water with iron and sulphuric acid , passed from the first reservoirs to the second , and thence into the immense globe , which was thus gradually inflated . These preparations occupied all the morning , and about 11 o'clock , the balloon was three-quarters full ; sufficiently so ; -- for as we rise , the atmospheric layers diminish in density , and the gas , confined within the aerostat , acquiring more elasticity , might otherwise burst its envelope . My calculations had furnished me with the exact measurement of gas required to carry my companions and myself to a considerable height . We were to ascend at noon . It was truly a magnificent spectacle , that of the impatient crowd who thronged around the reserved enclosure , inundated the entire square and adjoining streets , and covered the neighbouring houses from the basements to the slated roofs .