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What exactly is an ounce of powder?


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When the dosage of a particular powder, such as Sodium Bromide, is specified in "ounces per gallons of water", are the ounces measured by volume or weight?

How is it legal (or even safe) that the label does not provide this information?

Dan C.

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For dry ingredients an ounce is by weight. For liquid ingredients it's by volume. Same as in cooking. Think about it this way. An ounce by volume of water, mercury, and heavy cream all will have the same volume ( but different weights), while an ounce by weigh of ball bearings, baking soda, and feathers would have the same weight but very different volumes.

With pool and spa dry chemicals some might be fine powders (dichlor), some might be pellets (CYA), and some might be chunks (calcium chloride dihydrate) so an ounce by weight would not be the same volume for any of them.

The ONLY time an ounce by weight and by volume are the same is for water. This is considered common knowledge (and common sense) so it's not on labels.

An inexpensive digital kitchen scale and PLASTIC kitchen liquid measuring cups and spoons (and perhaps a chart that shows equivalences such as 16 Tbls. in a cup and 3 tsp. in a Tbls.) are necessary pool and spa equipment that is often overlooked!

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Great advice on the scale and measuring cups.   I 'borrow' the kitchen scale from time to time, and have made a table of weight to volumes for the common dry products used in the tub.  I think I will take your advice, @waterbear and buy a new scale for the kitchen, and keep the old one in the shop.

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On 3/26/2022 at 2:46 PM, waterbear said:

For dry ingredients an ounce is by weight

I'm a scientific minded person and that's exactly what I would have thought. Unfortunately, this is not a cut-and-dry topic (no pun intended) and there's a reason I was confused ... I had called the manufacturer's help line (Leisure Time) and the service tech told me their dosage for the bromine powder (and *any* of their dry powder products) should be measured by volume in a small measuring cup.  So again I ask, how is it legal that the label does not explicitly state this?

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That is really strange and confusing.  I would imagine the labeling on the front of the package states the net quantity in weight?  Like Waterbear mentioned, any dry good is going to be measured by weight.  There are some cases where it may be a 'dry measure' which is volumetric but I dont think you see this very often. For example it might state '2 dry pints' but the 'dry' labeling would be critical here.  

What does the front measurement state? And what do the instructions say?

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  • 2 weeks later...

The front says "Net Contents: 16 OZ".  Next time I buy a new bottle, I plan to weigh it.

The directions for use says to add "one-half (1/2) ounce of Leisure Time Sodium Bromide for every 100 gallons of spa water" - full stop.

Strange and confusing indeed. Normally I wouldn't question it, but because they did not state the equivalent measurement in teaspoons or tablespoons, I called the 800 number. 

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6 hours ago, dcaputi said:

The front says "Net Contents: 16 OZ". 

According to "15 U.S. Code § 1453 - Requirements of labeling; placement, form, and contents of statement of quantity; supplemental statement of quantity" it would be weight since volume measure is specified to use the largest volume measurement which means it would say '1 pint". Also, since the Bottle also state that it is 453 grams this is a weight measurement and not volume as I originally stated in a previous post, and the rounding of 453g is specified in "NIST Handbook 133, Fourth Edition" for weight labeling.  If it were a volume measurement the bottle would also be labeled in either milliliters or liters, most likely as .47 liters. This is assuming it is a US pint and not an Imperial (UK) pint which is 20 ounces. The labeling in both grams and ounces can be clearly seen in the attached picture confirming that it's by weight. Also, the dosing would be by weight.

BE1_2048x.webp

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6 hours ago, dcaputi said:

Strange and confusing indeed. Normally I wouldn't question it, but because they did not state the equivalent measurement in teaspoons or tablespoons

This is because teaspoons and tablespoons are volume measures and they are specifying a weight measure.

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