Topic: Question for those that know about ratios

[pressurepros]

As far as I know, Phillip, I think where  you guys are going wrong is that you want the information of the 'sum' of the
parts to be explicit, where as I was always taught the information for the sum of the parts is implicit.  How else
could you interpret a ratio of 3:2 if you are expecting information of the total to be explicitly shown, is it always
the larger number?

Please allow your buzz to wear off, then re-post...

Philip this is the post that sent me a little sideways in your answer. I was comparing it to Chris' originally stated ratio of 4:1 (1:4). I don't blame Chris for being confused as when someone tells you to mix something 1:3 you assume one part compound to 3 parts compound. But when expressed as a dilution ratio it is actually 1:4.

But Chris' originally stated ratio was incorrect.  He specifically asked about "If you put 1 gallon of chemical "A" into 4 gallons of water".  That's a 1:5 ratio, and not a 1:4 ratio.


The confusion arises because there are applications where A:B is correct. For example, what is the student:teacher ratio.  But that is not the correct usage in this case because what we are ultimately interested in is the final mix ration expressed in terms of chemical strength (% or PPM).

In bold is why I made my assumption that Philip was incorrect. Chris was factoring ratios the same as you, Dan.

[Philip93]

Phillip here is a link that goes exactly with how I was taught about ratios...

It's different when you are talking about a ratio of objects (one TO another) versus a dilution/proportion (one IN another).  In terms of chemical concentrations, if you have 3 parts A and 2 parts B, the ratio 3:2 (3 TO 2) has no practical purpose. 3:5 (three IN five), however, tell you very specifically the final chemical strength, which is the variable of interest.

An example of one TO another, would be a roof pitch.  A 6:12 pitch has a run of 6 and a rise of 12.  In this case, expressing it as a 6:18 ratio serves no practical purpose because neither the run, the rise, or the hypotenuse is 18. You could say that the ratio was 6:3√2, but that would be useless for nearly all practical applications.

A chemical example of one TO another, would be molecular mixes.  Water has a 2:1 ratio of hydrogen to oxygen. In this case, expressing it as a 1:3 ratio serves no practical purpose because the molecules do not join and become 3 water molecules.

[Philip93]

One important point of this discussion is to recognize that a large percentage of people express chem ratios as A:B.  So when buying chems, equipment, or even just copying another persons recipe, make sure you know if they meant 2:3 or 2:5

[moody1]

I saw nothing wrong with Dan's website, and it says the same thing as yours Philip, unless I am missing something.  So, I tell me where you disagree below.

1:1    =     1 gallon of A and 1 gallon of B     =      2 total gallons      =       50% strength of B

2:1    =     2 gallons of A and 1 gallon of B    =      3 total gallons      =       33% strength of B

3:1    =     3 gallons of A and 1 gallon of B    =      4 total gallons      =       25% strength of B

4:1    =     4 gallons of A and 1 gallon of B    =      5 total gallons      =       20% strength of B

5:1    =     5 gallons of A and 1 gallon of B    =      6 total gallons      =       16.6% strength of B

If you agree with all of this, then I do not understand what was wrong with my original post.  If you disagree with this, then what ratio would you use to get a 50% solution of A:B?  And if you disagree, then the way I learned ratios in college was incorrect.  I know that the common use of 10:1 yields a 10%, but the common usage is incorrect.  A 10:1 solution actually yields a 9.09% solution.  The main disagreement seems to be that some are stating that you can add 1 gallon of SH or any chemical to 4 gallons of water and still have only 4 gallons.  This just simply doesn't work.  The common uses of ratios are nice because they create simpler percentages, but that does not mean they are correct.  

[moody1]

Phillip here is a link that goes exactly with how I was taught about ratios...

It's different when you are talking about a ratio of objects (one TO another) versus a dilution/proportion (one IN another).  In terms of chemical concentrations, if you have 3 parts A and 2 parts B, the ratio 3:2 (3 TO 2) has no practical purpose. 3:5 (three IN five), however, tell you very specifically the final chemical strength, which is the variable of interest.

An example of one TO another, would be a roof pitch.  A 6:12 pitch has a run of 6 and a rise of 12.  In this case, expressing it as a 6:18 ratio serves no practical purpose because neither the run, the rise, or the hypotenuse is 18. You could say that the ratio was 6:3√2, but that would be useless for nearly all practical applications.

A chemical example of one TO another, would be molecular mixes.  Water has a 2:1 ratio of hydrogen to oxygen. In this case, expressing it as a 1:3 ratio serves no practical purpose because the molecules do not join and become 3 water molecules.

If this is true, and it may be, then what would be the purpose of representing your data in a ratio format as opposed to a fractional format?  And please note that the link you gave uses one method for calculating 2:1, and a different method for calculating 4:1, 10:1, and 20:1.  Also, up top in the pink where they list common mixing ratios, they follow the same method that Dan and I suggest.  They seem to contradict themselves, not staying consistant with either method.  I now understand the premise of what you are saying, I'm just not sure I agree with it yet.

[Philip93]

And please note that the link you gave uses one method for calculating 2:1, and a different method for calculating 4:1, 10:1, and 20:1.  Also, up top in the pink where they list common mixing ratios, they follow the same method that Dan and I suggest.  They seem to contradict themselves, not staying consistant with either method.

I just noticed that.  Very bizarre.

As for how the ratios is expressed, it's very important that you make a distinction between "A to B" and "A in B".  For dilutions, it's expressed as "A in B" because what's ultimately relevant is the final chemical concentration in PPM.

[moody1]

And please note that the link you gave uses one method for calculating 2:1, and a different method for calculating 4:1, 10:1, and 20:1.  Also, up top in the pink where they list common mixing ratios, they follow the same method that Dan and I suggest.  They seem to contradict themselves, not staying consistant with either method.

I just noticed that.  Very bizarre.

As for how the ratios is expressed, it's very important that you make a distinction between "A to B" and "A in B".  For dilutions, it's expressed as "A in B" because what's ultimately relevant is the final chemical concentration in PPM.

I have now done more research, and what you are saying seems to be true with larger volumes that 1:10 means 1/10 as opposed to 1/11.  However, all source I found seem to use a direct ratio as opposed to a proportion when using small volumes.  I now agree with what you are saying because it seems to jive with what I have found everywhere else.  Herein lies the problem:  Going by that method, 1:1 would be a 100% solution instead of a 50%.  I think we all agree that 1:1 is commonly considered 50%.  The method must change somewhere between 1:1 and 1:10 (or 10:1).  The problem is that I cannot find an acceptable explanation for this change anywhere.

[plainpainter]

One important point of this discussion is to recognize that a large percentage of people express chem ratios as A:B.  So when buying chems, equipment, or even just copying another persons recipe, make sure you know if they meant 2:3 or 2:5

Yes I agree - I'd go one step further that the ':' terminology is practically useless, if you you mean the latter of 2:5 then I'd just use the simple 2/5 notation.  It just seemed to me that General pumps was using 4:1 and 20% final dilution interchangeably for their downstreamers.  So I took that to mean 4 parts water to 1 part chemical or a 1/5 final dilution which is 20%.

I guess I prefer water to chemical terminology vs. chemical-water final dilution to chemical terminology.