Talk:Five Weeks in a Balloon

Bias
The 'Racial Sterotypes' section of this article is incredibly biased. It needs to be removed or rewritten. There's nothing really special about these things, or the 'Treatment of African Wildlife'. These were simply the ways of the time.75.89.1.12 (talk) 16:32, 6 June 2008 (UTC)

Hot Air with Hydrogen
Does the story describe a hot air balloon with hydrogen?--69.122.62.231 (talk) 23:16, 4 September 2009 (UTC)


 * No, it describes a hydrogen balloon which is heated to increase volume and thus lift. Ingenious, but not realistic for the reasons mentioned in the main article.--Gautier lebon (talk) 18:31, 6 January 2010 (UTC)

Inconsistent scientific/technological reference
I like this section since I think it adds value to the article without detracting from Verne's work: after all, he is basically a science fiction writer. But the original version had no references at all. I think that what the original version said was correct, but I have not found it easy to document this through citations. I have added one note which contains multiple references and some calculations to support what is said in the first paragraph. And I've added other paragraphs with references. But I would appreciate it if people could (1) double-check what I added and (2) add additional references.--Gautier lebon (talk) 09:13, 9 January 2010 (UTC) yes someone should change it it to heated hydrogen balloon. — Preceding unsigned comment added by Theorginaltrainguy (talk • contribs) 11:25, 30 January 2013 (UTC)

Inconsistent scientific/technological reference
The description of the apparatus used to heat the hydrogen gas in the balloon is deeply flawed. Jules Verne states that it uses a powerful electric battery to electrolyze water into hydrogen and oxygen, and then burns resulting hydrogen in a blow-pipe. He also says that the apparatus weighs 700 pounds (including the battery) and it is able to process 25 gallons of water. This is physically impossible. Even using state-of-the-art 21st century batteries (e.g. lithium-ion batteries) and assuming zero losses, one needs over 4000 pounds of batteries to electrolyze that much water. A lithium-ion battery stores 160Wh/Kg, see. The electric power required to electrolyze hydrogen equivalent in energy content to 1.04 US gallons of gasoline is about 33 kWh, assuming perfect efficiency, see and. The resulting quantity of gas has an energy content of about 38 kWh (137 MJ), see Gasoline (note that this is more than the energy that was input, which is not possible according to the laws of conservation of energy--as noted above the estimate for the energy required to electrolyze the water assumed 100% efficiency, which is not realistic). The energy required to heat hydrogen is 14.3 joules per gram per degree, see Specific_heat. The total energy stored in 300 Kg of lithium-ion batteries would be about 48kWh, which could theoretically electrolyze hydrogen containing 55 kWh (198 MJ). This would be sufficient to heat about 275 kilos of hydrogen by 50 degrees. The specific volume of hydrogen is about 12 m3/Kg at 1 atmosphere and 20 degrees, see. The balloon described by Verne had a volume of 90 thousand cubic feet (2548 m3), see chapter 7 of his book. So it would require about 212 Kg of hydrogen to fill the balloon completely; Verne states that the hydrogen weighed about 125 Kg, which is consistent with starting with a balloon that was only half-full, in order to allow for expansion. Given that the energy contained in the battery could only heat the 125 Kg of hydrogen by 50 degrees twice, it is clear that there was nowhere near enough energy in the battery to sustain a five week flight, and this because the gas would cool over time and would need to be heated many times over (not to mention the fact that Verne states that the hydrogen was heated by more than 100 degrees more than once--again, well beyond the capacity of even a modern high-performance battery). This number should be increased by at least a factor of five if authentic mid-19th century batteries are to be used. It would have been far more realistic simply to electrolyze the water up front and to load a tank of compressed hydrogen onto the balloon (electrolysis of that quantity of water produces less than 25 pounds of hydrogen).

Further, it would have been more efficient to use the energy contained in the battery to heat the gas directly. Electrolysis of water is not 100% efficient. So some of the energy contained in the battery is wasted and the heat generated by burning the obtained hydrogen is less than the heat that could have been obtained by simply using a resistance connected to the battery. In fact, Verne implies that the described device is a perpetual motion machine, since he implies that greater energy can be obtained by electrolysis than could have been obtained from the battery directly: if this were true, then the obtained hydrogen could be used to boil water to create steam to power an electrical generator to create more electricity for the battery. This may have been a deliberate joke by Verne.

Though the novel goes into great detail with much of the calculations involving the lift power of the hydrogen balloon, and how to obtain the proper amount of volume through changes in temperature, are gaps in the logic. The balloon rises up when heated, and lowers as it is allowed to cool. This pattern is used as numerous plot points and is shown to be a somewhat quick process of cooling. At night, however, there is little mention of them maintaining the temperature through the night. Another gap in the scientific logic is the lack of reference to the effect of atmospheric temperature on the balloon itself, though the temperature is referenced as affecting the heating coil.

And it would be very dangerous to light a fire in the nacelle under a balloon filled with hydrogen.

Further, in Chapter 41, the load carried is progressively reduced in order to allow the balloon to rise higher and higher. But in fact a single load reduction would have been sufficient, because at that point the lift of the balloon would have exceeded the weight and it would have continued to rise until the volume of gas was reduced. (The density of air decreases with increasing altitude, thus reducing the lift at constant balloon volume, but the balloon would expand proportionately, due to decreasing air pressure, thus maintaining constant total lift.)

In Chapter 26, it says the doctor takes the balloon up to five miles (8 km). Later, in Chapter 29, in order to get over Mount Mendif, the doctor "by means of a temperature increased to one hundred and eighty degrees, gave the balloon a fresh ascensional force of nearly sixteen hundred pounds, and it went up to an elevation of more than eight thousand feet" which is noted as being "the greatest height attained during the journey." If this is meant to imply that the doctor went eight thousand feet above Mount Mendif, at a height greater than five miles (8 km), Jules Verne would have greatly underestimated the drop in temperature and how much heat would have been required to keep the balloon at that height for any length of time.

At the time when the book was first written, lands to the north and northwest of Lake Victoria were still poorly known to Europeans. Jules Verne makes a few inaccurate predictions here, such as placing the source of the Nile river at 2°40′N (instead of 0°45′N); claiming that this source is just over 90 mi from of Gondokoro (the actual distance is closer to 300 miles); not mentioning Lake Albert at all (it was not discovered by Europeans until after the publication of the book). Much of the geography described further in the book is completely fictional. For example, coordinates given for the "desert oasis" in chapter 27 correspond to a location in a savanna region of southern Chad, less than twenty miles (32 km) from a big river.