Accuracy: measuring liquid concentrate with syringe vs powder with spoon?

[Alan Townsend]

I will admit to never using measuring spoons for homebrew developers mostly due to the complex nature of using so many spoons of one size and so many other spoons of another size and have always used a scale for weighing powdered components. I recently spent much time working with a homebrew developer concentrate MC-glycerol and had significant issues with consistent results due to measurement errors that I had not expected. A few days ago I ordered this set of measuring spoons on Amazona:

https://www.amazon.com/dp/B09ST488G5?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

This set of five spoons goes down to 1/64 of a teaspoon. I was not aware these were available, and it changes everything for me. 1/64 of a teaspoon gives me exactly 0.05 grams of metol, exactly what I need for 500ml Gainers original MC developer mixed 1:1. Another very clever aspect of Gainers developers from 1993 is they use even teaspoon measures for 3 chemicals in the case of the metol version. My version of this, which uses sodium carbonate monohydrate rather than anhydrous, and is for 1/4 the amount of developer is:

sodium carbonate monohydrate 1 tsp
ascorbic acid 1/8 tsp
metol 1/64 tsp
water 500 ml

This is extremely easy to mix, and very accurate provided a good box cutter blade is used to level the spoons. I was always envious of people using measuring syringes to mix their homebrew developers from liquid concentrates that were made using a good scale with fair amounts of chemical to make stable solutions in glycols and other polyols for stability, and always wanted to try that, only without using phenidone. When I started doing this, I have nothing but trouble mixing my concentrates in glycerol solution with a measuring syringe. The troubles included:

1. The 10 ml syringes I got read 1 ml when the syringe was empty. This was very confusing since I always thought empty meant zero. So getting in the habit of adding 1 to everything I need was challenging.

2. Very difficult reading the scale on the syringes. Mine have 3 different units but the ml scale is very hard to read. I only want an ml scale, but got some extras at no charge. When measuring a fluid, you have to fill the syringe, then discharge until a certain level is read, but that level is invisible, so you have to subtract from the higher number and use that since you can only read upward not downward. For example, I need 3.6 ml. So after filling, I push the plunger down until I see 5 ml -0.4 ml to known when to stop. So I need to add 2 and then suptract 0.4, not easy to remember, so have to repeat several times to get it right.

3. After filling the syringe and then slowly ejecting excess until reaching desired amount, while holding it but putting zero pressure on the plunger, solution continues to dribble out slowly due to gravity, density, and oiliness. How do I lock the plunger? Put the cap back on, which takes a few seconds? Try to instantly dump the syringe without a time delay? This may be worse for glycerol than glycol due to greater density.

4, Thermal expansion or compression. Glycerol has a large amount of thermal expansion with heat, so to have an accurate measure, I need to stabilize the temperature of the cooncentrate along with the water I use for mixing. I have not being doing this, but should have, since my work space is always 5-6 df colder than the 70 deg. F I stability with.

I wasn't aware of all these issues with measuring syringes. It may just be the ones I bought. For myself and others using metol, I believe it much easier an more accurate to use measuring spoons with chemistry more compatible with them. I also was not aware I could get 1/64 tsp measuring spoon. If 1/256 tsp are available, users of penidone could use them, although it may be hard to breath without blowing it away.

Comments and suggestions are very welcome, especially if people can steer me to better measuring syringes meaning those that read zero when empty and have clearly marked ml only.

 

[mshchem]

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[MattKing]

Best choice is to use weight, not volume, plus ~lab grade equipment and techniques.
For many things though - where precision isn't as necessary - things like spoons are fine.

 

[RalphLambrecht]

I will admit to never using measuring spoons for homebrew developers mostly due to the complex nature of using so many spoons of one size and so many other spoons of another size and have always used a scale for weighing powdered components. I recently spent much time working with a homebrew developer concentrate MC-glycerol and had significant issues with consistent results due to measurement errors that I had not expected. A few days ago I ordered this set of measuring spoons on Amazona:

https://www.amazon.com/dp/B09ST488G5?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

This set of five spoons goes down to 1/64 of a teaspoon. I was not aware these were available, and it changes everything for me. 1/64 of a teaspoon gives me exactly 0.05 grams of metol, exactly what I need for 500ml Gainers original MC developer mixed 1:1. Another very clever aspect of Gainers developers from 1993 is they use even teaspoon measures for 3 chemicals in the case of the metol version. My version of this, which uses sodium carbonate monohydrate rather than anhydrous, and is for 1/4 the amount of developer is:

sodium carbonate monohydrate 1 tsp
ascorbic acid 1/8 tsp
metol 1/64 tsp
water 500 ml

This is extremely easy to mix, and very accurate provided a good box cutter blade is used to level the spoons. I was always envious of people using measuring syringes to mix their homebrew developers from liquid concentrates that were made using a good scale with fair amounts of chemical to make stable solutions in glycols and other polyols for stability, and always wanted to try that, only without using phenidone. When I started doing this, I have nothing but trouble mixing my concentrates in glycerol solution with a measuring syringe. The troubles included:

1. The 10 ml syringes I got read 1 ml when the syringe was empty. This was very confusing since I always thought empty meant zero. So getting in the habit of adding 1 to everything I need was challenging.

2. Very difficult reading the scale on the syringes. Mine have 3 different units but the ml scale is very hard to read. I only want an ml scale, but got some extras at no charge. When measuring a fluid, you have to fill the syringe, then discharge until a certain level is read, but that level is invisible, so you have to subtract from the higher number and use that since you can only read upward not downward. For example, I need 3.6 ml. So after filling, I push the plunger down until I see 5 ml -0.4 ml to known when to stop. So I need to add 2 and then suptract 0.4, not easy to remember, so have to repeat several times to get it right.

3. After filling the syringe and then slowly ejecting excess until reaching desired amount, while holding it but putting zero pressure on the plunger, solution continues to dribble out slowly due to gravity, density, and oiliness. How do I lock the plunger? Put the cap back on, which takes a few seconds? Try to instantly dump the syringe without a time delay? This may be worse for glycerol than glycol due to greater density.

4, Thermal expansion or compression. Glycerol has a large amount of thermal expansion with heat, so to have an accurate measure, I need to stabilize the temperature of the cooncentrate along with the water I use for mixing. I have not being doing this, but should have, since my work space is always 5-6 df colder than the 70 deg. F I stability with.

I wasn't aware of all these issues with measuring syringes. It may just be the ones I bought. For myself and others using metol, I believe it much easier an more accurate to use measuring spoons with chemistry more compatible with them. I also was not aware I could get 1/64 tsp measuring spoon. If 1/256 tsp are available, users of penidone could use them, although it may be hard to breath without blowing it away.

Comments and suggestions are very welcome, especially if people can steer me to better measuring syringes meaning those that read zero when empty and have clearly marked ml only.

I always stuck to measuring in grams. Everything else goes against my grain a bit, but I'm getting closer to your question. My syringes (bought at a local pharmacy) read '0' when empty. I fill them fully, then empty them to the desired amount, and then use that amount. pretty straightforward. I haven't found anything similar on Amazon, but I could possibly take a picture of one.

 

[gbroadbridge]

1. The 10 ml syringes I got read 1 ml when the syringe was empty.

Are you saying that the syringe does not have a zero marking?

 

[Alan Townsend]

Are you saying that the syringe does not have a zero marking?

No, the zero marking is at the bottom of the black rubber plunger, so can't be read due to black text against black background having no contrast. Reading above that black rubber plunger is the 1 which can be read against the white color of the plunger just above that black piece. It's a poor design. In other words, the black rubber piece at the bottom of the plunger covers the readings between 0 and 1 ml so those are not readable. I must read above the black piece where there is a white plastic behind the markings.

 

[gbroadbridge]

No, the zero marking is at the bottom of the black rubber plunger, so can't be read due to black text against black background having no contrast. Reading above that black rubber plunger is the 1 which can be read against the white color of the plunger just above that black piece. It's a poor design. In other words, the black rubber piece at the bottom of the plunger covers the readings between 0 and 1 ml so those are not readable. I must read above the black piece where there is a white plastic behind the markings.

But when you immerse in liquid and pull up the syringe so that the 1ml marking is visible at the bottom of the plunger you have 1ml of liquid in the syringe - so I don't understand the issue.

 

[Alan Townsend]

But when you immerse in liquid and pull up the syringe so that the 1ml marking is visible at the bottom of the plunger you have 1ml of liquid in the syringe - so I don't understand the issue.

If I were measuring milk, I would be able to read the scale below the black rubber since there is something behind the scale to read against. It's the contrast. With a clear liquid, there is nothing there to reflect light. I guess I could put a piece of white tape on the outside opposite the scale, that might work. I will not set up a light to read the scale using transmission, that would be very inconvenient, and the whole reason for using these syringes was convenience. I find them inaccurate and inconvenient to use. The dripping after I stop pushing on the plunger is another big problem. I guess I can put my finger over the end. If I used one of these many times a day I could get used to them, but that's not going to be the case. As a wild guess, your eyesight may be better than mine, especially in low light conditions like I have in my darkroom area. Thanks for the response.

 

[wiltw]

The issue with 'partial' mix using powders is that one cannot have certainty that the proper proportions of the various chemical components is evenly distrubuted throughout the 'mix'. You could end up with too much of one ingredient and too little of another ingredient, and simply shaking the mix does not evenly distribute each of the many component chemicals.

 

[gbroadbridge]

As a wild guess, your eyesight may be better than mine, especially in low light conditions like I have in my darkroom area. Thanks for the response.

Oh right, I just use the torch built into my phone if I'm struggling to see measurements even with my glasses

 

[Yezishu]

In my lab experience, using a measuring spoon(or analytical balance) is convenient for powders, while a syringe/graduated dropper(or pipette) is better for liquids. There shouldn't be a need to mix the developer in a darkroom environment? A piece of white paper and desk lamp as background is enough to see the scale via transmitted light.

When using a syringe for sticky liquid, I usually allow for a bit of waste and imprecision. For example, draw about 9.x ml into a 10 ml syringe, discharge some until it hits the 9 ml mark, and wipe off any excess liquid. Then, dispense 4 ml into one bottle (bringing the scale down to 5 ml) and another 4 ml into a second bottle (ending at the 1 ml mark). Stopping the flow requires more than just releasing the pressure. You have to grip the plunger to keep it from moving. We have plastic syringes ranging from 1ml to 50ml, as well as some 0.1ml specialty glass ones. In addition to manual use, they are also used in syringe pumps.

 

[beemermark]

I have a number of scales so I use them. But I also think (and have used) measuring spoons. Good ones are just as accurate. Don't loose sleep over it. It's not rocket science.

 

[koraks]

I generally use pasteur pipettes, not syringes. Easier to use. This type:

I bought a box of...IDK, 2500 or so? This will last me several lifetimes. I've included it in my last will & testament.

As to your question - it doesn't really matter. There's a fudge factor either way and that's fine. You'll never notice it. Same for minutiae like thermal expansion of the liquid, whether or not the last drip is part of the volume etc.

Use whatever is convenient. Don't worry about the rest.

 

[Doremus Scudder]

I use all the methods mentioned above. Spoon measures have an inherent inaccuracy, even if you "calibrate" them to the specific granularity of the powdered chemical you're using by checking weight for a given volume of a particular batch first. That said, they are fast and easy and work well for mixing up things that have larger margins of error (e.g., simple print developers). I use my quad balance to measure dry chemicals for things that require precision or which are hard to get relatively consistent results from spoon measures (clumpy chemicals, etc.).

I use regular syringes for small amounts of liquid concentrates. The trick here is to have the right size syringe for the amount of liquid you need. Trying to measure 1ml on a 10ml is inherently inaccurate. Using a 2ml syringe marked in half or quarter ml works a lot better. You get the idea. Pipettes are great too, I just have lots of syringes.

For larger amounts of liquids, graduated cylinders are the ticket, in the right size, or course. Ideally, the target volume should be well up on the scale, not wallowing around on the bottom.

Best

Doremus

 

[pentaxuser]

Best choice is to use weight, not volume, plus ~lab grade equipment and techniques.
For many things though - where precision isn't as necessary - things like spoons are fine.

Very true. I usually judge the right amount of some liquid medicines by what we Brits call "swigs" or in technical terms mouthfuls from the bottle

pentaxuser

 

[BobUK]

At one time I had some syringes that read 1 at the bottom end of the plunger when it could travel no further down the tube.

I always took this to be the volume of the Luer taper below the cylindrical tube. The bit that the needle is fitted to.

Later syringes I purchased are zero at the bottom of the plunger tube, but there is still that small amount of volume in the Luer taper fitting.
That small amount of liquid in the end end taper is retained in the syringe, no matter how watery the fluid is.


I don't know if it is surface tension or air pressure holding the last drops in the end.
Perhaps some one here with a bit more knowledge on such things could enlighten me.



Thanks in advance.

 

[MattKing]

If you want to measure 4 ml out of a 5 ml syringe, fill it to the 5 ml line and then dispense the liquid until it is down to the 1 ml line.

 

[Maris]

In high accuracy analytical chemistry there are two types of precision pipettes; those calibrated to "contain" a volume and those calibrated to "deliver" a volume. I'm sure the same constraints apply to droppers and syringes when dispensing exact volumes of liquid. The answer to the problem is prior calibration, preferably by a gravimetric technique, and then consistent use. Mixing up "contain" and "deliver" pipettes was a big no no in the laboratories where I worked.

 

[dynachrome]

I have many different sets of measuring spoons and for the developers I am likely to make up, they are accurate enough. Somewhere in my garage or basement is a Mettler P1000 laboratory scale which I have been meaning to calibrate for years. When making up D-76 or D-23, being off by 1ml will make no difference. Many years ago when I used HC-110, I made up the stock solution and diluted from there. I used Dil. B. When I used Rodinal or PCTEA at 1:50, I poured the developer i to a 10ml graduate. The water was at the correct temperature. I poured some of it into the graduate a few times to get all of the developer out. It never occurred to me to use the old HC-110 at 1:31 directly to get Dil. B. It wasn't worth the trouble. If the sun comes out and it's not too cold, I will shoot some film and try the Black/White&Green I recently bought. I think I will use 1:50 instead of 1:49.

I will relate a story which I may have told before. When I was 14 I had been using D-76 but wanted to try Agfa Rodinal. I read that the best way to pour out the developer was to push a hypodermic needle through the rubber stopper. I walked into Drezen's pharmacy on Allerton Avenue on The Bronx. The pharmacist asked me what I needed. I told him I wanted to purchase a hypodermic needle. He asked me what I wanted to do with it. When I told him, he said "Get out of here before I call the police "

 

[Yezishu]

At one time I had some syringes that read 1 at the bottom end of the plunger when it could travel no further down the tube.

I always took this to be the volume of the Luer taper below the cylindrical tube. The bit that the needle is fitted to.

Later syringes I purchased are zero at the bottom of the plunger tube, but there is still that small amount of volume in the Luer taper fitting.
That small amount of liquid in the end end taper is retained in the syringe, no matter how watery the fluid is.


I don't know if it is surface tension or air pressure holding the last drops in the end.
Perhaps some one here with a bit more knowledge on such things could enlighten me.



Thanks in advance.

They accepted these drops as a necessary loss for accuracy. In more precise tools like 1ml syringes, the plunger usually has a 'long nose' or or dead-space-reducing tip to minimize the residual waste of the stock solution.

 

[Scott J.]

Regarding syringes:

1) If it's a syringe with a black rubber plunger, you read the liquid volume from the bottom of the plunger (the side toward the Luer tip). The convex shape of the plunger bottom is designed to mate to concave bottom of the syringe. Everything in between is your measured volume.
2) The small dead volume contained in the Luer tip (<0.1 mL) is already accounted for in the gradations on the syringe, as some fluid remains in the Luer tip because of vacuum and capillary force. There's actually an ISO standard that specifies the max allowable volume for different sized syringes.
3) You can purchase syringes that don't have rubber plungers and are a little easier to read (e.g.,: https://www.amazon.com/Sterile-Syringe-Individually-Measuring-Scientific/dp/B0D2KYQGMG). Labs use these for chemicals (e.g., esters) that normally dissolve rubber.
4) Syringes designed for children's medicine typically don't have rubber plungers, are easy to read, and are similarly convenient for measuring small volumes of photo chemistry.
5) For viscous chemicals (e.g., HC-110), you can attach a large gauge "dispensing needle" (e.g., 4-inch x 10-gauge) that will allow you to reach into a bottle opening and draw fluid into the syringe without gooping up the outside of your syringe. These are really handy for developers that use propylene glycol as a solvent.

 

[bernard_L]

I have a couple of syringes where I fitted a ~7-10cm length of clear flexible pvc tubing on the tip of the syringe. The ID of the tube is ~2mm. This allows pumping viscous liquids, like HC-110 or glycol-based devs. And reaching to the bottom of a 250ml bottle.

I do not push the plunger to the bottom when measuring, because the liquid in the length of PVC tubing might be dispensed as well if there is an air bubble trapped below the plunger. Measure by the meniscus. Dispense between two lines, the final one being not at the bottom. Then return the contents of the tubing to the bottle.

I believe the accuracy for a typical 6ml volume is 5% or better; good enough for amateur work.

.

 

[RalphLambrecht]

Regarding syringes:

1) If it's a syringe with a black rubber plunger, you read the liquid volume from the bottom of the plunger (the side toward the Luer tip). The convex shape of the plunger bottom is designed to mate to concave bottom of the syringe. Everything in between is your measured volume.
2) The small dead volume contained in the Luer tip (<0.1 mL) is already accounted for in the gradations on the syringe, as some fluid remains in the Luer tip because of vacuum and capillary force. There's actually an ISO standard that specifies the max allowable volume for different sized syringes.
3) You can purchase syringes that don't have rubber plungers and are a little easier to read (e.g.,: https://www.amazon.com/Sterile-Syringe-Individually-Measuring-Scientific/dp/B0D2KYQGMG). Labs use these for chemicals (e.g., esters) that normally dissolve rubber.
4) Syringes designed for children's medicine typically don't have rubber plungers, are easy to read, and are similarly convenient for measuring small volumes of photo chemistry.
5) For viscous chemicals (e.g., HC-110), you can attach a large gauge "dispensing needle" (e.g., 4-inch x 10-gauge) that will allow you to reach into a bottle opening and draw fluid into the syringe without gooping up the outside of your syringe. These are really handy for developers that use propylene glycol as a solvent.

mine look exactly like these but have a green plunger.

 

[Petrochemist]

At one time I had some syringes that read 1 at the bottom end of the plunger when it could travel no further down the tube.

I always took this to be the volume of the Luer taper below the cylindrical tube. The bit that the needle is fitted to.

Later syringes I purchased are zero at the bottom of the plunger tube, but there is still that small amount of volume in the Luer taper fitting.
That small amount of liquid in the end end taper is retained in the syringe, no matter how watery the fluid is.


I don't know if it is surface tension or air pressure holding the last drops in the end.
Perhaps some one here with a bit more knowledge on such things could enlighten me.



Thanks in advance.

The volume of the needle (if used) can be fairly significant too. The only syringes I've used that expel all the liquid drawn up are microlitre sized plunger in needle models, that I doubt anyone uses for photography.

When using syringes to make up standards it was standard practice to weigh quantities (usually to 0.0001g) for ultimate accuracy. Photographic materials can get away with somewhat cruder measurements, but I still prefer to use weight for everything other than the final total volume.

 

[Petrochemist]

I have a couple of syringes where I fitted a ~7-10cm length of clear flexible pvc tubing on the tip of the syringe. The ID of the tube is ~2mm. This allows pumping viscous liquids, like HC-110 or glycol-based devs. And reaching to the bottom of a 250ml bottle.

I do not push the plunger to the bottom when measuring, because the liquid in the length of PVC tubing might be dispensed as well if there is an air bubble trapped below the plunger. Measure by the meniscus. Dispense between two lines, the final one being not at the bottom. Then return the contents of the tubing to the bottle.

I believe the accuracy for a typical 6ml volume is 5% or better; good enough for amateur work.

View attachment 418555
.

I used to have some 18" long wide leur needles for drawing up viscous liquids & reaching the bottom of winchesters. I would then change to a short dispensing needle for expelling.