Weighing liquid chemicals

FujiLove · Aug 6, 2015

I'll apologise in advance if this is a dumb question, but does anyone know whether the densities of RA4 concentrates are the same as, or close to water? I'm asking as I plan to mix some small amounts of working solution this weekend and would like to be as accurate as possible with relatively small amounts. My cunning plan is to use the chemical scales, but obviously that's not going to work if the liquids don't weight close to 1kg/litre.

Any ideas?

RalphLambrecht · Aug 6, 2015

FujiLove said:
I'll apologise in advance if this is a dumb question, but does anyone know whether the densities of RA4 concentrates are the same as, or close to water? I'm asking as I plan to mix some small amounts of working solution this weekend and would like to be as accurate as possible with relatively small amounts. My cunning plan is to use the chemical scales, but obviously that's not going to work if the liquids don't weight close to 1kg/litre.

Any ideas?

Not sure if correct,but ,Itreat 1mlas 1g for simplicity

Ian Grant · Aug 6, 2015

Why not use a small measuring cylinder or a syringe, the SG of the liquid concentrates will differ and weight isn't accurate enough. I have a range of syringes up to about 50ml and graduates down to 10ml. Both would be accurate enough.

Ian

Gerald C Koch · Aug 6, 2015

NO, you would have to take into consideration each liquid's specific gravity.

FujiLove · Aug 6, 2015

Feared that may be the case. I think syringes may be the way to go, but unfortunately the ones I have now only go to 10ml and I'd rather not measure several times with those as that will lead to inaccuracies. Time to look for big syringes I think!

AgX · Aug 6, 2015

A range of measuring cylinders is a basic in photo-lab equipment.

As indicated for very small volumes one can use graduated syringes, but also graduated pipettes.

Sirius Glass · Aug 6, 2015

Gerald C Koch said:
NO, you would have to take into consideration each liquid's specific gravity.

Hence the prior posts recommending use of graduated cylinders for measurement.

RalphLambrecht · Aug 6, 2015

AgX said:
A range of measuring cylinders is a basic in photo-lab equipment.

As indicated for very small volumes one can use graduated syringes, but also graduated pipettes.

Tht's right and you can buy them for pennies at the chemist or the Apothem unless you look like a user.

RobC · Aug 6, 2015

if you have the liquid chemical and you have water, then you can measure out the same amount of both and put on scales one at a time and adjust volume of one until it weighs same as the other. You then have their relative densities and can work from that.

But I rekon they won't be too far from equal with same volume since the liquid chemical likely has a lot of water in it water.

Gerald C Koch · Aug 6, 2015

To me the whole purpose of liquid chemistry is convenience. Weighing out solutions goes counter to that. Then there is the chance of making a math error. As mentioned previously in the thread every darkroom should have a set of graduate cylinders.

Gerald C Koch · Aug 6, 2015

RobC said:
But I rekon they won't be too far from equal with same volume since the liquid chemical likely has a lot of water in it water.

Speaking generally it depends, you would run into trouble with something like Rodinal Sp Gr 1.383.

Sirius Glass · Aug 6, 2015

Gerald C Koch said:
To me the whole purpose of liquid chemistry is convenience. Weighing out solutions goes counter to that. Then there is the chance of making a math error. As mentioned previously in the thread every darkroom should have a set of graduate cylinders.

Use liquid measurements. Why ask for problems when we can make enough mistakes to cause enough problems?

Photo Engineer · Aug 6, 2015

Parts of these kits contain no water, but rather contain TEA or other organic solvents. They are also quite viscous making measurement of volume difficult when it comes time to pour. A lot can stay behind in the measuring vessel.

Therefore, it is helpful to measure by volume in small quantities or with syringes where the liquid can be dispensed accurately, but it is helpful to measure by weight as an absolute value for larger quantities. In other words the method used can vary, but the method proposed in the OP is wrong, wrong, wrong. See the density figure in the post above.

PE

Sirius Glass · Aug 6, 2015

Photo Engineer said:
Parts of these kits contain no water, but rather contain TEA or other organic solvents. They are also quite viscous making measurement of volume difficult when it comes time to pour. A lot can stay behind in the measuring vessel.

Therefore, it is helpful to measure by volume in small quantities or with syringes where the liquid can be dispensed accurately, but it is helpful to measure by weight as an absolute value for larger quantities. In other words the method used can vary, but the method proposed in the OP is wrong, wrong, wrong. See the density figure in the post above.

PE

How about measuring is a measuring vessel, such as a graduated cylinder or with a syringe, then rinsing with water that is then used to put in mixing vessel. That way the remaining residue would be transmitted to the mixing vessel.

Gerald C Koch · Aug 6, 2015

When using pipettes it is important to know that there are two kinds To deliver TD and To Contain TC. TC pipettes should always be rinsed out and the rinsings included toward the total volume. With TD ones that fluid remaining in the pipette should NEVER be added to the total volume. There should be a TD or TC on each pipette. For disposable ones this may appear only on the box.

Graduate cylinders are considered to be TC measuring devices and syringes TD dnes.

Photo Engineer · Aug 7, 2015

And TD depends on viscosity.

PE

FujiLove · Aug 7, 2015

I'm completely sold on using the syringe method. I had a look at the Kodak RA4 data sheet, and for my planned 500ml working solutions I'll need 20ml of parts A and C and 9.8ml part B which would be a little tricky even with small measuring cylinders. I've got a few 10ml syringes, so I'll use those.

AgX · Aug 7, 2015

Gerald C Koch said:
Graduate cylinders are considered to be TC measuring devices and syringes TD dnes.

In (medical) syringes there practically remains a residue in the cone, thus they are graduated for TC.

Photo Engineer · Aug 7, 2015

If chemistry is left in the syringe after use, it is TD not TC, otherwise you would have to somehow expel the residual amount.

PE

AgX · Aug 9, 2015

Medical syringes always contain residue in the cone, which cannot be delivered. Thus that amount is calculated into the graduation (if it is that precise anyway).

Sirius Glass · Aug 9, 2015

AgX said:
Medical syringes always contain residue in the cone, which cannot be delivered. Thus that amount is calculated into the graduation (if it is that precise anyway).

After expelling the reagent, draw in water and flush out the residue several times adding the water to the chemical mix. That moves all the reagent to the mixing bucket and start adding water to the mix. That is good chemistry practice and good darkroom practice.

Weighing liquid chemicals

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