Reading Anne McCaffrey's Dragonrider novels back in the day, I always pictured the "agenothree" flame-throwers borne by the queen riders as spraying flame at the falling thread.

Later in the series, it is revealed that "agenothree" is really HNO3, or Nitric Acid. While I seem to remember that the flame throwers spit fire, that does not fit in with the actual behaviour of Nitric Acid.

Is there anywhere in the books that either describes them as either spraying a liquid mist or (incorrectly) spraying streams of flame?


While I can't think of any instance where it specifically says, it is inferred that the flamethrowers fire a stream of flame. The first mention of agenothree is in Dragonsdawn:

Now, a sweep from bow to stern in a one-second blast chars as much Thread for the range of these throwers. Catch the end of the stuff and fire runs back up most of it. Don’t waste the HNO3.

(Bolding mine)

And here's a forum post about this exact question:

If I am reading correctly, the books ALL imply that the HNO3 was not just sprayed as a mist/vapour (although it WAS used as a liquid in AWOP to erode the anti-matter engines) but was ignited to produce flame. HOW?

I remember other references to them shooting flame, but I can't recall any quotes off the top of my head.

A couple other possibilities:

  • They may use both HNO3 sprayers and flamethrowers in different situations.
  • HNO3, when mixed with certain organic compounds such as turpentine, becomes self-igniting.

There's quite a bit of interesting discussion on this topic here.

Upon further reading, I think I have it figured out. Originally upon landing, and for some time after, flamethrowers were used. The oldtimers Lessa brought forward were still using flamethrowers. However, flamethrowers need a bit higher technology level than the 'current' Pernese have, in order to pressurize and contain the highly flammable gasses. As the machinery broke down, they switched from using true flamethrowers to agenothree sprayers, but by tradition, they were still called flamethrowers. Agenothree sprayers originally came about because it's much safer to use HNO3 (which is also a fertilizer) over/around farmland than it is to use a true flamethrower, which would burn crops as well.

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  • Oh no! D: I was hoping that I misremembered. I will cling to the turpentine explanation as a viable alternative. That link to the discussion is very interesting. – S. Albano Sep 12 '12 at 4:29
  • Yeah, I got distracted from answering for a bit because of that :D – SaintWacko Sep 12 '12 at 4:35
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    Also, I'm going to have to make Anne McCaffrey the next author I read through (again), as soon as I finish the Xanth series. – SaintWacko Sep 12 '12 at 4:45
  • @S.Albano - I added some new information I found. – SaintWacko Sep 12 '12 at 14:00

The agenothree shooters are, in fact, described explicitly as not shooting fire. In Dragonflight, before Lessa brought forth the Oldtimers and their equipment, Mastersmith Fandarel couldn't get a design for a flamethrower that actually worked, so he considered using agenothree instead - as an acid to destroy the thread directly, not as a fuel source:

There are, it is true, fluids which burn and sear. We use an acid to etch design on daggers and ornamental metals. We of the Craft call it agenothree.

Also, it's specifically mentioned that when used on dragonback it would disperse, and even serve as a fertilizer for crops on the ground, as Fandarel tells Lord Vincet of Nerat:

"Little man, agenothree in diluted form is what you use to fertilize your plants in the spring. [...] It would be better if we could get the spray up high in the air. Then it would float down and dissipate harmlessly fertilizing very evenly, too."

And even some of the Oldtimers, with their fancy flamethrowers, could see the use of a thread-destroyer that could serve as a fertilizer:

D'ram, particularly, was very much interested in Fandarel's agenothree sprayer, considering it better than thrown-flame, since it would also act as a fertilizer.

(All quotes from Dragonflight. Sorry not to have specific references, but my book is out on loan, so I'm quoting from an unpaged ebook)

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  • I wonder what is up with the quote from Dragon's Dawn then. It sounds like it was correct in the earlier stories, but was messed up later on perhaps? – S. Albano Sep 12 '12 at 15:08
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    I've gone over all HNO3 references in Dragon's Dawn again, and I think it's actually ok. the only explicit reference, the one SaintWacko mentioned, doesn't actually say the HNO3 caught fire, only that the thread did, once hit. A bit vague, I know, but might be what she had in mind. – Avner Shahar-Kashtan Sep 12 '12 at 15:24
  • A description of an interesting chemical reaction where a liquid causes something to combust seems like the sort of detail that authors like to include. I think that she had the science right in the first book, and it just fell through the cracks when writing about the origins of agenothree in Dragon's Dawn. It is a much cooler thing to picture though. :) – S. Albano Sep 13 '12 at 16:58

I am constantly bemused by the reference to Nitric Acid; Agenothree is clearly Silver Nitrate, it says so - Ag (Silver), NO3 (Nitrate). I don't understand why it isn't obvious to everyone.

Silver Nitrate is an excellent protein precipitant, and would make short work of the descending "thread".

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  • How good of a fertilizer is it? – Organic Marble Aug 25 '17 at 12:12
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    The glossary of terms at the end of the book explicitly calls it to be HNO3. Think of how these letters would be pronounced, not written. – Avner Shahar-Kashtan Sep 15 '17 at 13:51
  • "agenothree: a common chemical on Pern, HNO3". – Avner Shahar-Kashtan Sep 15 '17 at 13:52
  • I read in one of the books (dunno which one) that one of the 'standby duties' of a dragonrider was searing hilltops to keep them barren, thus ensuring any stray thread couldn't get a hold there. Would spraying a fertiliser not be counter to this idea? – DannyMcG Sep 17 '17 at 2:49
  • @Danny3414 It's a quote from Dragonflight, and it refers to having dragons sear the hilltops with flame, both to keep plants from growing and to practice flight formations and flame-breathing techniques. – Avner Shahar-Kashtan Sep 17 '17 at 4:02

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