# How do you calculate the combined weight of items that lack weight?

### Rules Questions

I'm looking to give the party a pound of phosphorous and a pound of magnesium. Both items are weightless in the portions used for alchemy, so presumably a pound of them is a considerably bigger portion. How big should such a portion be? And how much should it cost? Without knowing a rule of thumb for how to add up multiples of a weightless item, I'm staring at a zero. Help?

I usually figure that anything marked weightless that clearly can't be weightless, at minimum, 1/20th of a pound, or the weight of a gold coin.

These substances, as alchemy reagents, seem heavier to me, so I would put one dose at 0.1 pounds.

One rule of thumb is to assign 10 weightless items to be 1 pound of encumbrance. It's also the old D&D weight for 1 gold coin (10 per pound)

So you might say that an alchemy portion is 1.6 ounces or 3 Tablespoons (about what a shot glass would hold).

I've heard of 1/10th, 1/20th, or 1/25th based on folks I have asked in real life. Is there any consensus?

My only advice is to choose something and stick with it.
Consistency can be more important than accuracy most the time.

It really doesn't matter in many respects. Select the one that reflects the number of uses that you want your players to have, make a note and be consistent.

If you want to get fancy assign a different value to each component, so they get 12 uses of phosphorous in that 1lb, and 26 uses from that 1lb of magnesium.

well first off one is assuming a level of technology that may not be there.
Are high temperature kilns and oxygen free ovens available?
What are the raw materials and where are they coming from?
How are they processed.
Salts or metals? There's quite a bit of difference and reducing salts into metals can be a complex process.
So -
Phosphorous salts are easy enough to come by and pure phosphorous is very rare. White phosphorous is something used in water to ignite flash paper (the magic trick where you see a note suddenly engulfed in flames, as the solution dries the phosphor ignites setting the paper on fire). You do understand that white phosphor ignites on contact with air (oxygen). lol... it might be a bit hazardous to carry around in a cloth bag so a tiny vial with a few grams of white phosphorous might be all that's obtainable. Red phosphorous is more stable. Calcium phosphate, calcium orthophosphate, or ferrous phosphate would be alternatives.
Magnesium as salts are easy to come by, the metal is not naturally found pure. Unlike phosphorus, magnesium is produced commercially using electricity (electrolysis). That's out of the range of alchemy (sublimation, calcination, etc). Magnesium sulfate is useful, but not sparkly in fireworks.

so what do you expect them to do with these minerals? Is there something in mind?

on the weight issue, weight is one thing, encumbrance another. Most of the ENC is twice the weight. For game purposes english units are used, so look up grains, drams, ounces... troy and tower weights... lol...

Density is what you are looking for, that's kg/m^3 or g/cm^3(cc)
White Phosphorous(WP), P, is 1.823 g/cc, Mg is 1.738 g/cc
1 pound(lb) is 453.6 grams(g), 1m^3=264.17 gallons or 29.5735cc=1 fl ounce (of water).
so 1 lb of WP is 453.6/1.83=247.87cc or 8.4 fl ounces, so a little over a cup of volume (if a solid dense mass). Likely to be 1 oz WP in a vial of water with a bit of oil, so I'd say 4 lbs of ENC due to the 16 (very dangerous) 1/4 ENC vials each containing a bit over 1 Tablespoon of WP.

and 1 lb of Mg is 453.6/1.738=261cc or 8.83 fl oz, so a little over a cup of volume again (if a solid dense mass). Likely to be a powder, so I'd double the volume. Still I'd use an ENC of 2 due to the density.

edit - bag of Mg powder to 1 ENC as it's dense. This is based on a waterskin of 4 lbs coming in at 4 ENC.
I would not reduce the ENC due to packaging on the white phosphorous. If a vial cracks your backback is going to ignite sometime later...

When I first read the topic and OP, I thought you were asking how much a pound of phosphorous or magnesium would weigh.

Anyway, there are a few ways to figure it out. If you note a Magnesium Golem, it takes 1,000 lbs of magnesium to construct (mixed with other rare chemicals) which costs 4,000 gold. Depending on what proportion of the cost is taken up by those non-magnesium materials, the cost of pure magnesium is no higher than 4 gold/lb if bought in bulk.

Next, there's this FAQ:

FAQ wrote:

Weapons: There are melee weapons in Ultimate Combat (pages 131 to 132) with a weight of "—". If these weapons are primarily metal (like the kerambit), how do you calculate the cost of creating mithral versions of these weapons?

Treat these weapons as 1/2 lb weapons for the purpose of creating a mithral version of the weapon.

If you go buy this rule, two doses of alchemical magensium or phosphorous would be one lb; the Magnesium would cost 2 gold/lb and the phosphorous would cost 4 sp. The Magnesium certainly falls within the expected range as it is less than 4 gold/lb. However, there are exceptions. For instance, 20 arrows is, by default, 3 lbs (0.15 lb/arrow). Crossbow bolts are 1 lb/10 (0.1 lb/bolt) and repeating bolts are twice that. So the half pound figure probably serves best for an upper-bound for the weight as anything higher than a half lb would likely have already been rounded up to a full pound.

Another example is the Skydragon Firework. It's 10 lbs and consists of a cardboard tube filled with the alchemical preparation which consists of 100 total doses of ingredients which are calcinated (burned down). The weight of the wrapping is likely negligible so that would suggest that the weight of the ingredients after being burned down is around 10 units/lb (thus, fewer units/lb of unprocessed ingredients).

Personally, I think a good balance point is probably 4 units/lb. So 1 alchemical "dose" of an ingredient with "-" weight is about 0.25lbs. This matches the price of the magnesium golem at 4 gold/lb of magnesium and counts the price of the "rare chemicals" as negligible next to the shear bulk of magnesium being used (and probably matches whatever you save by getting bulk magnesium).

I'm looking to give the party a pound of phosphorous and a pound of magnesium. Both items are weightless in the portions used for alchemy, so presumably a pound of them is a considerably bigger portion. How big should such a portion be? And how much should it cost? Without knowing a rule of thumb for how to add up multiples of a weightless item, I'm staring at a zero. Help?

Unless it's being carried by someone who zoinked their Strength down to 5 or less, I don't bother with niggling details at the ounce level.

well - I don't believe that the authors were aware of certain small measurements and material components tend to get done with a wide brush (general unspecific statements) but they did make statements in spell about a drop or pinch.
So being pedantic (this is a Rules Thread... lol);
1 tsp = 1 fl dram = 5mL = 5cc{water} = 60 drop = 60 minim = 8 dash = 16 pinches = 32 smidgens. This can vary based on the diameter of the pipette and the viscosity or the liquid, but 1/60th tsp is about right. US and British units can vary a bit but I'd use the above.

The CRB and other books have never really come out and said the Spell Component Pouch \$5GP, 2lb, has N number of uses or can cast N number of spell levels. It has specifically been avoided. The whole thing is about having to have them so if they are taken away a spellcaster's selection is very limited.

Esoteric components were more concerned about the GP cost of the component per casting rather than the actual item and weight itself.
Essentially it's up to your GM.

Moving onto what's practical or fair...
In a simple format (PFS) they'd never run out once you purchased the Spell Component Pouch.
In a totally generic treatment I'd say 1 copper per spell level or 250 spell levels in the Spell Component Pouch (figuring the pouch is half the value) and 250 components weigh 1 lb or 0.064oz or about 1.89mL (density of water). That's pretty generous.