D-23 Powder chemicals - weight vs volume

Mick Fagan said:

The official measurements for a tablespoon in the USA is 14.8ml while the UK and Canada have it at 15ml, meanwhile a tablespoon in Australia is 20ml.

Source Margaret Fulton's Complete Cookbook, second edition 1977, she is an Australian.

I checked a couple of online sources, which confirm the above measurements. I would suggest photographic chemistry measurement is best done via weight, but I'm not a chemist by a long shot.......

Click to expand...

Reminds me of a friend of mine who studied to become a research pharmacist.
She was involved with some research that highlighted the problems that occurred when people used household spoons - nominally described as teaspoons and tablespoons, but not the accurately graduated ones - to dispense liquid medication to their children.

I have a triple-beam balance scale and a digital scale. I still use my spoon recipes for things like print developer or mixing a bleach bath. For things that really need precision, I haul out the scales and/or make percentage stock solutions that I can measure as liquid volumes. For many things, however, once you've figured out your spoon recipe (by checking weights with your scale), you can save a lot of time just using measuring spoons. I use the same set every time, use the same batch of powdered chemicals and have great results.

You only need to be as accurate as you need to be...

Plus, despite the belief that weighing things out is more accurate, it isn't always the case. Chemicals that absorb moisture change in weight over time, adding water weight through their useful life once the container has been opened, so that last 50g of anhydrous whatever likely contains a lot less of the chemical and a lot more water than the first 50g did when the container was first opened. Using chemicals that are relatively stable helps this, but many still vary in moisture content over time.

Doremus

For routine D23 I purchase the 5 lb Sodium Sulfite (lasts forever and is used in everything), 100g Metol , and the 1lb sodium metaborate. Don't bother with divided unless you have some serious contrast issues to manage.

MattKing said:

some research that highlighted the problems that occurred when people used household spoons - nominally described as teaspoons and tablespoons, but not the accurately graduated ones - to dispense liquid medication to their children.

Click to expand...

This is a large part of why cough syrup (at least in USA) these days usually includes a dosing cup marked with adult and child dosage levels (though they're called off in milliliters). In contrast, of course, to my long-standing "calibrated tongue" method of dosing myself...