This is just going to be a series of threads in which I am going to take various pieces of the Spiral Knights world, be they materials or concepts or other, and apply as much science as I possibly can.

How much science, you ask?

Let me put it this way - with the object in the subject header (the fiery goop Salamanders spit) - I have found out the most likely way that said spit is created.

First, the chemical that burns and makes that delightful red fire effect is: Calcium/Lithium/Caesium - Chloride. Any would do, but only Lithium or Caesium would be pyrophoric (self-igniting in the presence of warm air) to light the rest of the chemicals (But caesium is FAR too reactive to be consumed). Assuming that the spit IS created from a chlorinated Alkali metal then I can presume that the said molecule would have to be created. The initial thought would be some internal reaction to create the Lithium or Calcium-Chloride, and that is sensible; the stomach of a Salamander can be acidic (and chlorinated) to the point where lithium carbonate spontaneously forms inside their stomachs, but the sheer stomach-ache from this reaction (not mentioning all the other acid-based reactions inevitably going on) would make for one hell of a life. Evolution would undoubtedly scratch this method out.
So where else? Let us reconsider the idea of an internal synthesis, but replace the acidic nature of the stomach with a smidge more neutral one. After years of gremlin growth and industry it would not be unthinkable for acid rain - sulphuric acid and hydrogen chloride - to form, and if acid rain were to fall then if is entirely possible that a chromalisk would drink it and then adapt to thrive with it. And then it could consume some pieces of calcium or lithium carbonate after its drink of acid and the dissociated H+ ions could react with the carbonate groups and leave the alkalis to from chlorides with the chloride. Et viola! Alkali Carbonate that burns red!

But how does this compound not get absorbed and excreted by their digestive system, I ask myself? And I already had the answer before I even thought to ask. They have no intestines. Only a sack of walled muscle that allows the colonies of bacteria it received from its mother's milk in its youth to act as enzymes and fold and lyse the food it eats. The bacteria which was unable to survive the acidic environment brought on by the tart liquid the mammal drinks eventually died and their host along with them. Those that could would consume that which their host could not (grass and tubers) whilst they also digested that which the host could consume for nutrients and the like (meat) into molecules more readily absorb-able by the stomach walls.
This is what led to a freak mutation that left a poor chromalisk with bacteria that could form palmitic and napthanic acid (both components of napalm but with palmitic acid being a natural fatty acid) and a stomach wall that could NOT absorb it. And that's where the jelly substance comes from.
The way it is expelled is through the walls of the stomach convulsing explosively and forcing the accreted material up and out, usually also in an explosive manner. The reason why the stomach is able to do this is due to the fact that the stomach wall muscles resemble cardiac muscle that can be forced into action by the skeletal muscle covering the outside of it. A truly strange evolutionary adaptation. If I ever magically receive the ability to draw I will attempt to give a diagram of this organ.

Finally the reason why the regurgitated material is ignited at all is because of a pouch on either side of the Salamanders face that is able to hold material. The material in question being ground metal flakes. A protective secretion a.k.a. saliva stops them from harming the creature whilst being stored. When they need to be expelled the Salamander forces a vacuum within the pouches which causes metal flakes to gather at the enter/exit sphincter. When the Salamander expels the Alkali-carbonate/ethanoic acid mixture the creature may engage a series of muscles within its pouches which expel the now-dry flakes at a velocity that produces a spark, hopefully catching the expelled material within its arc.
The capability to expel an arc of fire would explain why Salamanders have such tough, broad teeth; for grinding down metals, no doubt.

And through these three processes; the accumulation of lithium carbonate in the stomach, expulsion of said material, and an ability to create a spark from the mouth, the Salamander can shoot fiery goop. The similar situation can be assumed to explain how other chromalisk sub-species can shoot their own special variety of goop i.e. diet and genetics.

Any questions?

What did I just read?
Exactly what you just read. If you want an easy-to-understand breakdown then give me a moment to let my brain process what I just wrote. Or ask the person behind you.
As for what you just read: You have just read a thesis on how chromalisks MAY have evolved a way to shoot fiery and other kinds of goop. Unfortunately I KNOW that what I just wrote would get thrown not only in the bin but would get mailed back to me after having been thrown into the bin to show me how terrible it was if I ever showed it to an accredited thesis committee.

So why did you do this?
Because I wanted to spend a couple of hours on this.