How many drops in a ml? Does size matter?!

[Tetsab]

Hello all, three weeks in but still just a beginner and far from an expert so thought I'd start my first-ever thread here in the 'innocents quarter'.

Having seen various quotes on various threads as to how many drops constitute a millilitre, 20, 30 etc I've got to ask what seems an obvious question now I've got myself all puzzled.

I have three different bottle sizes - 3.7ml testers from Johnson's Creek, really teeny weeny bottles. Really teeny weeny droppers as well. Do fit nicely in my old cigarette case, though.
A 15ml bottle from Smokester (e-cigs.co.uk) which has a larger and quite intricately-made dropper.
A 30ml bottle from Totally Wicked - even BIGGER but straightforwardly-made dropper.

Surely there will be different numbers of drops from each of these droppers to make a millilitre so it actually depends on what size bottle you've got? If I'm topping up a cartridge I can get about 10 drops from the JC dropper into it before it starts looking full again but only need two or three from the TW dropper.

I am interested because I know on the continent they dispense medicines in dropper bottles with instructions to use 'X' number of drops for a dose so had always assumed it was a standard measurement but now I'm not so sure!

I'm sure all the guys will tell us that size matters, but being a girl I've always thought that wasn't the only criterion...

[ZambucaLu]

Hi Tetsab. I had a similar question. People will say something like "just put 2 or 3 drops on the atomizer, but be careful not to flood it". Well, right now I am using a little plastic 10ml bottle where I had to snip off the top. The drop from that is a lot smaller than the 35ml bottle I have where the hole was already made. So I can't really tell how much I'm using yet.

Are most eyedropper holes a standard size and is that what people are talking about when they say "a drop"? It's not a big issue for me but it was something I thought about.

I can't recall how many drops they said were in a ml but I can guarantee that the little pinhead opening I have in my small bottle would not equal the drops they are talking about.

Lu

[BarryK]

It just occurred to me that if you see how many drops you can get into a teaspoon - that's gonna be within a knats **ck of 5 millilitres.

Better still, a plastic medicine spoon is spot on 5mil ..............

Barry

[usehername]

There are 180 drops in a 3.7 ml bottle of JC using the supplied dropper.
It takes 146 drops from the typical plastic squeeze bottle to fill the same 3.7 ml bottle.
Interestingly, using a JC dropper instead of the squeeze bottle it will take 190 drops to fill that 3.7 ml bottle. The contents of the squeeze bottle is typical Chinese fluid. somewhat thicker than the JC juice.

[usehername]

Sorry .. cant edit.. If you split the difference in viscosity to 185 drops in that sample bottle you get 50 drops per ml.

[ApOsTle51]

correct, all depends in the viscosity of the liquid becuase i'm sure gravity and surface tension limits are the same where ever you are in the world.

If you used the same liquid but a different dropper, drop size will remain exactly similar

[Tetsab]

Ye gods, Usehername - did you actually COUNT to find that out to such precision??? ...and I thought I could be a bit OCD at times!! If so, my gratitude for your dedication to finding out the truth.

ApO, I think I understand what you're saying about the viscosity making a difference, although it seems a big difference between the JC and the TW I have here at home. Does this indicate that TW is MUCH thicker? That would mean that number of drops per ml would vary according to the brand of liquid you're using, so this might account for the difference between the figures people are quoting. Imagine it gets even worse when you make up your own mixtures.

My reading of Usehername's figures was that three tests were carried out with the result that 3.7ml of JC was 180 drops, but the other two were BOTH with the Chinese liquid and gave different results, 146 drops with the squeeze bottle but 190 with the JC dropper.

I had kind of thought that maybe the size of the dropper's aperture might affect the size of drop? Because although surface tension might be the same (unless you're on top of a mountain, maybe?) there is less glass for the drop to 'hold on' to with a smaller opening so a spherical drop would form and fall that much sooner? My Physics & Chemistry 'O'-Level seems an awfully long time ago so I quite accept I'm probably talking c**p!

Ho hum, could waste centuries considering these matters of very small moment...

[usehername]

Correct Tetsab. The second and third measures were with the same chinese fluid. First out of the common plastic squeeze bottle and finally with the JC dropper.
Not sure why I do these things...

[Kate]

I found this

"According to Webster dictionary, "drop" indicates the smallest volume of a liquid that may be measured. The size of drop may vary with the viscosity of the liquid."

Drop (unit - Wikipedia, the free encyclopedia)

[Bertrand]

I would have thought density, surface tension and dropper diameters would be the deciding factors. My speculation is that at the point the downward force due to gravity (dependent on liquid density) overcomes the upward force due to the liquid's tendency to cohere (dependent on surface tension and dropper diameter) the drop would break off.

I don't see how viscosity would really come into play except in extreme cases like glass "droplets" (you'll be waiting a while for them to form...)