Teaspoon measuring

[ronlamarsh]

Hi all my chart does not include ammonium chloride or sodium citrate does anyone out there have the gram equivalent data for these chemicals i.e. grams/teaspoon ???? Thanks

[Bruce Watson]

Originally Posted by ronlamarsh

Hi all my chart does not include ammonium chloride or sodium citrate does anyone out there have the gram equivalent data for these chemicals i.e. grams/teaspoon ???? Thanks

One is an indicator of mass, the other is an indicator of physical volume. Those two concepts are not the same thing. At all.

If you want to be consistent, buy a scale. Accurate scales for darkroom work aren't that expensive, and the precision of your darkroom work will improve considerably. Just sayin'.

[Sirius Glass]

I believe that the OP wants a chart with the weight in grams.

Steve

[Robert Hall]

The problem is that many chems are hygroscopic. The gain water weight as the get older. (Sounds familiar ) That means the amounts will be all over the place because you have no real starting point.

Scales are cheap, $50 will get you a great scale. Get one that weighs in .1 or tenth grams. Trust me, you will be very happy you did.

[Photo Engineer]

Using teaspoon measurements can result in an error factor of as much as 20% or +/- 10% from batch to batch of chemical based on the fineness of the crystals in a given batch.

If you can accept that much variation in your formulas, go right ahead.

PE

[sanking]

Originally Posted by Bruce Watson

One is an indicator of mass, the other is an indicator of physical volume. Those two concepts are not the same thing. At all.

If you want to be consistent, buy a scale. Accurate scales for darkroom work aren't that expensive, and the precision of your darkroom work will improve considerably. Just sayin'.

I agree with Bruce. Why measure with a teaspoon when the cost of accurate scales is so inexpensive.

Have a look here, for example. http://www.balances.com/

Sandy King

[fotch]

I have purchase several analog Ohaus scales used of of epay, never more than $15-20 including shipping. I know the electronic are easier to use but they will not last as long. I also would worry about accuracy with the cheap ones.

[gainer]

Originally Posted by Bruce Watson

One is an indicator of mass, the other is an indicator of physical volume. Those two concepts are not the same thing. At all.

If you want to be consistent, buy a scale. Accurate scales for darkroom work aren't that expensive, and the precision of your darkroom work will improve considerably. Just sayin'.

The argument of hygroscopicity is an argument against the consistency of weight measurements. The concepts of mass and volume are connected by the concept of density. Every time you measure both mass and volume, you can compute density. If you know density and measure volume, you can compute weight. That said, let me remind you that the computation of density to a certain number of significant figures can be accomplished accurately by the use of volume and weight measuring devices of much less precision if large enough quantities are measured, so that the ratio of mass or volume to precision of those measurements is as desired. I explained all this in my article of 1973, "Kitchen Tested Soups", in Petersen's Photographic. That being done, then smaller amounts of mass can be determined by use of appropriately precise volumetric measurements. In the case of hygroscopic chemicals, the best bet is a solution saturated at a temperature lower than your normal lab temperature.

If we were rich as Croesus, we might purchase only chemicals of reagent grade and weigh them to the fraction of a milligram. We would be foolish to do so without first ascertaining whether such precision is necessary for our purposes. Every solution we make for the processing of B&W film has some tolerance for error in measurement or quality of its ingredients. When you are prepared to tell me what those tolerances are, we can argue some more about efficient ways to achieve them.

PE is by former employment and current avocation and, for that matter, business, a laboratory research chemist. Here, the shoe is on the other foot. You don't know what you have unless you know your ingredients. Still, a mixture that depends on reagent grade chemicals and labaratory precision of measurements may cost more to produce than customers will pay, so it is worthwhile to do an analysis of sensitivity to variance in measurement and quality of ingredients.

Would you believe that every time I have mixed 1/8 tsp Metol, 1/2 tsp ascorbic acid, and 1 tsp sodium carbonate in a quart of water since 1973 the solution has given me the same activity?

[BradS]

classic....the scientist vs the engineers.

For whatever it is worth any engineer worth his salt will immediately point out that a product or process that is not robust against minor variations is worthless...or simply put, un-economic, not feasible.

and... sheesh! guys, the OP asked a simple question....and all but one jumped on him for measuring his chems with a teaspoon. Nice. What a nice bunch of helpful folks....

For the OP, I looked up the density of Ammonium cloride and found it to be, 1.5274 g/ml . I figure a standard teaspoon is 5ml so, I get 7.6 grams per teaspoon. In a similar fashion, I get 8.5 grams per teaspoon for sodium citrate.

[Photo Engineer]

Brad;

You are right.....

Of course, if we don't pass things on correctly to the following generations, they are doomed to doing it incorrectly and this level of accuracy will slowly degenerat. So, what would you do if you were me? Would you teach the wrong things? Give inaccurate formulas? I am trying to teach, and others seem to not care. This is a tough position to be in for me. Especially when Patrick says that "since 1973 the solution has given me the same activity" when in fact, he may be using the same batch of chemicals or he may not have made exact side-by-side comparisons. IDK.

If you use the same ingredients from the same bottle with the same crystal habit, this method will work, but if you change batches or crystal size or habit, then the volumetric measures can be off by 20%.

Now, tell me, what would you say in my place?

PE