DIY Liquids not measuring correctly

[glassmanoak]

WHAT! You are ABSOLUTELY wrong!

Using the meniscus with air above it to measure in a syringe is just wrong. It may be easier for you to get reproducible results; it is the right method for graduated cylinders, beakers, flasks and the like (which are calibrated to use the meniscus, and calibrated to the meniscus of a specific liquid). But that's not how a syringe works. Using that method, the actual volume of liquid would change depending on the needle attached. That is there is fluid in the needle and the bit that screws to the syringe and there is fluid in the body of the syringe. If you use a bigger or longer needle then there will be more fluid if you just measure by meniscus.

Of Course! But when you are injecting the fluid into your mixture, you stop when the meniscus is at the ZERO mark on the syringe. You don't inject the fluid that is in the needle and below the ZERO mark into your mixture. You put that fluid back into your bottle.

What you do is this (for say 1ml):

draw in 1ml of air into syringe.
insert syringe into bottle and hold upside down.
inject air into bottle.
We don't have this situation. We are't using a sealed bottle! This isn't a medical vial! How can we hold the bottle upside down?

draw .5ml of fluid. There will be a small air buble at the needle end of the syringe, this is the air that was in the needle tip part. inject this back into the bottle. let's say push .25ml or so + the air back in the bottle.
draw fluid down to 1ml mark. You now have 1ml of fluid in the body of the syringe, and a needle full of fluid, and no air bubbles anywhere.
remove and inject into wherever.
there will still be fluid in the needle bit, that is waste and you just pump it out into a vaper towel or something.

If you measure by meniscus with an air buble between the liquid and the plunger, you'll end up with the liquid in the syringe (1ml) PLUS whatever liquid it takes to fill the needle part. If you change needle tips to a longer or larger bore needle and keep using the meniscus method you'll end up with two different amounts of liquid because there will be more in the needle part.

If you instead do it properly, you'll end up with the same amount of liquid no matter which tip you use. You could have a 3 foot long 1/8" needle and still get the same amount of liquid.
I agree, but your analysis just doesn't fit the DIY situation.

Yes I know I'm being nitpicky and at the scale of things we're measuring something like being off by 0.05ml isn't going to be much of a difference. If you use the same syringe and same needle all the time, the meniscus method will give you the same amount of liquid each time, but it's won't be what you were trying to measure on the scale. Syringes are not closed bottomed cylinders and aren't designed to be read the same way.

I agree that a syringe is not a graduated cylinder, but if you use the syringe as I have indicated and stop at the Zero mark, it is IN FACT, a graduated cylinder.

We really are being picking some major nits here, but I contend, that if you use your syringe in the manner indicated, that all the fluid that is between your measure mark and the zero mark is the amount of fluid you desire. You could use a 3 foot needle that is 10 guage and still wind up with the desired amount. Arguing about the amount of fluid in the needle may seem nitpicky, but it is a significant amount if you are making a small batch.
I can't think of a MORE accurate method of measuring small amounts of liquid. We don't have 1 ml or 3 ml graduated cylinders. We have to turn a syringe into one, which we have done using my method.
You can't even use a syringe without a needle and be more accurate, because of the fluid between the bottom of the syringe and the zero mark.

I hope everyone has managed to read through this lengthy debate, but I feel that using this meniscus method is a significant improvement in precise measurements, and repeatable recipes, in any quantity.

 

[vsummer1]

That is assuming you have a bottle that you can put air into. Most of mine are open mouthed, so adding air will accomplish nothing, and holding them upside down will certainly cause them to dump out their contents. Thus I use the needle to get the stuff into the syringe, which then becomes a graduated cylinder with a needle attached and can be measured by the meniscus.

I am not injecting expensive medications into patients so if I am off by such a minute amount it doesn't stress me much.

 

[nanovapr]

Is the tip of your plunger flat? If so, using it like a graduated cylinder won't be off by much, aside from the fact that it was never calibrated/manufactured to be used like that.

Is the tip of your plunger conical? If so, you have extra air/headspace, that was intended to be filled with liquid.

These are very small differences. I think it is more important to be consistent, that to be PPM accurate. Find a way that works for you, and stick with it.

 

[glassmanoak]

Is the tip of your plunger flat? If so, using it like a graduated cylinder won't be off by much, aside from the fact that it was never calibrated/manufactured to be used like that.

Is the tip of your plunger conical? If so, you have extra air/headspace, that was intended to be filled with liquid.

These are very small differences. I think it is more important to be consistent, that to be PPM accurate. Find a way that works for you, and stick with it.

I totally agree! It's only important in making up small batches. And for the .... retentives of the world, like ME.

PS: The shape of the plunger doesn't matter in the method I described

 

[nanovapr]

I use pierceable caps on sealed bottles, so I hold the bottle upside down, syringe pointing up. The headspace would make a difference for me, albeit small.

 

[glassmanoak]

I use pierceable caps on sealed bottles, so I hold the bottle upside down, syringe pointing up. The headspace would make a difference for me, albeit small.

Where do you get those?

 

[vsummer1]

If you are concerned with such minuscule, accurate measurements, you shouldn't use a syringe at all. buy a graduated pipette. They are the most accurate measure of all. In this application, you aren't going to really need pharmaceutical precision which cannot be achieved by a syringe in any case.

So in all reality, this whole conversation should be geared towards NOT using a syringe at all.

 

[zoiDman]

Just a little quick Math.

The Nominal Inside Diameter (ID) of an 18 ga Hypodermic Needle is .033"

If the Hypodermic Needle is 1" Long, the Volume inside the Needle in Cubic Inches is V = (π(.033/2)^2) x 1 => V =.0009 Cubic Inches.

If 1 Cubic Inch is Approximately Equal to 16.3871ml => .0009 Cubic Inch = .0140ml

So a 1 Inch Long 18 ga Hypodermic Needle contains .0140ml of Volume.

To put how Small this Volume is in Perspective, .0140ml Error with respect to 10ml is .14%. Or if there are 20 Drops in 1ml, than .0140ml is Equivalent to .0007 Drops.

My Suggestion is if you are Really Concerned with making a Measurements at the .0140ml Level that you might Check the Accuracy of your Syringes and or Graduated Cylinders. Because .0140ml probably Exceeds the Level of Accuracy of your Syringes or Graduated Cylinder by a Factor of 7.

You also may want to consider at what Temperature and Atmospheric Pressure you are Measuring your Liquids. .0140ml may approach the Relative Difference of Volume do to Thermal Expansion when there is a 15 Degree Fahrenheit Change in Temperature.

A Fundamental Rule of Measurement is that if the Amount being measured is Less than the Accuracy of the Measuring Equipment, that Accuracy Cannot Be Guaranteed. Precision perhaps but Not Accuracy.

 

[Spazmelda]

I would like this post multiple times if I could.

Just a little quick Math.

The Nominal Inside Diameter (ID) of an 18 ga Hypodermic Needle is .033"

If the Hypodermic Needle is 1" Long, the Volume inside the Needle in Cubic Inches is V = (π(.033/2)^2) x 1 => V =.0009 Cubic Inches.

If 1 Cubic Inch is Approximately Equal to 16.3871ml => .0009 Cubic Inch = .0140ml

So a 1 Inch Long 18 ga Hypodermic Needle contains .0140ml of Volume.

To put how Small this Volume is in Perspective, .0140ml Error with respect to 10ml is .14%. Or if there are 20 Drops in 1ml, than .0140ml is Equivalent to .0007 Drops.

My Suggestion is if you are Really Concerned with making a Measurements at the .0140ml Level that you might Check the Accuracy of your Syringes and or Graduated Cylinders. Because .0140ml probably Exceeds the Level of Accuracy of your Syringes or Graduated Cylinder by a Factor of 7.

You also may want to consider at what Temperature and Atmospheric Pressure you are Measuring your Liquids. .0140ml may approach the Relative Difference of Volume do to Thermal Expansion when there is a 15 Degree Fahrenheit Change in Temperature.

A Fundamental Rule of Measurement is that if the Amount being measured is Less than the Accuracy of the Measuring Equipment, that Accuracy Cannot Be Guaranteed. Precision perhaps but No Accuracy.

 

[zoiDman]

I would like this post multiple times if I could.

So I take it you don’t count Individual Grains when you add salt to a Spaghetti Sauce?

LOL

 

[vsummer1]

^ Yeah, that. Just in case you care, I can't taste the difference in my juices from batch to batch using a syringe anyway. Seriously, there are several threads on tastes changing from hour to hour, day to day etc.

 

[zoiDman]

^ Yeah, that. Just in case you care, I can't taste the difference in my juices from batch to batch using a syringe anyway. Seriously, there are several threads on tastes changing from hour to hour, day to day etc.

I hear you.

Some get Stuck on Numbers. That's Cool.

But sometimes the Numbers become So Small that their Meaning can be Questioned.

 

[Spazmelda]

So I take it you don’t count Individual Grains when you add Salt to a Spaghetti Sauce?

LOL

Kosher or table salt?

 

[nanovapr]

Where do you get those?

I use these pierceable caps, presumably there are many places. In another DIY thread, someone said they had the rubber break down and get mushy. I haven't had that, I use them until they are swiss cheese.

All my flavors and nic are in sealed bottles with pierceable tops, knocking them over isn't a risk. PG/VG are in pourable bottles.

I mix under two big premises all the time:
1. What's the biggest possible safety thing that can go wrong?
2. What's the biggest mess I can make?

Into the final mixing bottle go flavorings and PG/VG first. Up until that point, only the mixing bottle is left open, I can only make a mess. The nic goes in last, and the mixing bottle becomes the biggest possible safety thing that can go wrong. I put a lid on it, end of immediate risk.

 

[zoiDman]

Kosher or table salt?

I use Sea Salt because It has a More Reliable Molar Mass.

 

[vsummer1]

I use Sea Salt because It has a More Reliable Molar Mass.

And would that be white? or Black? or Pink?
Savory Spice Shop, Inc. - Hawaii Kai’s Palm Island Gourmet™ Sea Salt, Black Lava

 

[zoiDman]

Black Salt?

Arguing over .0140ml is one thing. But Black Salt is just Wrong.

 

[glassmanoak]

Just a little quick Math.


A Fundamental Rule of Measurement is that if the Amount being measured is Less than the Accuracy of the Measuring Equipment, that Accuracy Cannot Be Guaranteed. Precision perhaps but Not Accuracy.

I really like this analysis, zoiDman. It makes me feel like I've been trying to count the number of angels contained in a syringe needle.

 

[zoiDman]

I really like this analysis, zoiDman. It makes me feel like I've been trying to count the number of angels contained in a syringe needle.

LOL

Don't get mewrong. Doing Accurate DIY is Good Thing. But there does come a Point where you can be More and More Accurate and NEVER tatse the Difference.

It can become an Exercise in Futility and can lead to Frustration.

The Retail DIY Mixers I know talk about a +/- 3% Accuracy as Completely Expectable.

 

[BikerBob]

I probably should upgrade to some better equipment if I want to get in better control of my vaping levels. I looked up some graduated cylinders this evening, but the only ones I could find were like 50mL+. Do you know of a good source to around a 10mL graduated cylinder online? Plastic, glass, doesn't matter to me.

Graduated Cylinder,All Glass,10ml: Amazon.com: Industrial & Scientific 10ml glass. $5
Graduated Cylinder,All Glass,25ml: Amazon.com: Industrial & Scientific 25ml glass. $6.50
add a pint of PG USP and VG USP, and you can get to the 'free shipping' mark...or if you know someone with Amazon Prime, they get free shipping on a lot of things.