pH

Methods of measuring pH
To measure the pH of a solution,  a digital pH meter, or pH papers  such as litmus are used.
These methods can be expensive, especially  if you are buying the pool test strips.
pH meters begin selling for  $70 and usually run $120 if you can even find one.

Red Cabbage is happening
You really don't have to use either of them, as nature provides us with pH indicators in the form of plant pigments which change color over different pH ranges. One of the very best is red cabbage. Red cabbage juice will function over a wide pH range, from as low as pH 1 up to pH 13.
Preparation
There are many ways to prepare the indicators,
My favorite is to chop up 1/2 of a head of red cabbage
place it in a pot of water, then
bringing it to a boil,
let it cool down slowly the color slowly drains out of the cells.
Filter and discard the solids,
evaporate and concentrate the juice   Don't over heat it too much, it will get brownish if you do.
Then dip blotter paper or  paper towels , in the juice. Spread them out to dry, then dip them again so they get a double dose
If you wish you may iron them flat, run through a shredder for individual strips.
I usually just put drops on a full sheet.

pH measurements    What to measure
Measurements are taken on polar (water soluble) solutions only.

Taking a pH reading on a  non-polar (oil soluble) solution is futile.
If you do get a  pH reading you are actually measuring the pH of any polar solvent residue trapped in with the non-polar.
this may be an indication of purity of the non-polar and not much else
 
 

Above are pictures of the actual, indicator in water at the various pH's, Below is a color bar.

Do you see a  problem in determining various pH from the top photo?
Many of the water colors look the same
pH 3     thru  pH 6
pH 7     thru  pH 9
pH 11  and   pH12

The timing of the color indicator is not included.
Most  indicators have a certain time window in which they should be read,  this true with red cabbage also
The pH is read within  3 -10 seconds and compared to the lower color bar.

examples
pH-11
A drop of a solution at pH 11 will change  from purple to yellow-green very fast (3-10 seconds),  and slowly  continue changing until it is yellow. If you check the paper after 30 seconds, you would not know if the pH was 11 or 12 since both would be yellow
pH12
At  pH of 12+ the drop will turn the paper from purple to green to yellow  very fast (3-10 seconds)

pH7.2
At the very first sign of blue within a few seconds of placing the drop, stop, no more acid is needed,.
As you are shooting for the correct neutral pH you will be adding acid and bringing it down from pH 12+.
so the tests will appear yellow then green then one test will be blue after 3 seconds

 Accuracy  vs  Precision
Accuracy - is closeness to the actual true value
Precision - is internal closeness of a set of measurements

Using the paper is too kewl,  because before long you won't  care what the pH is.
All that will matter is that you saw the color change from purple to green to yellow immediately after putting a drop on the paper.
At the neutral  end you first saw a bit of blueness so you knew you were at the neutral pH spot.
It is so perfect, I marvel still at all the go-go, that was dreamt up with this red cabbage paper.
The pH paper is accurate to at least  0.4 of a pH unit or even better  when you include the time factor.
After doing it a few times your precision will be excellent 0.1 - 0.2  pH unit
The pH meters are accurate to  0.2 pH units
 
 

One pH reading
Have developed a way to almost avoid  taking a pH reading at all.
You may only need to take one reading,  to verify the upper point has been reached
I suggest you save this method for the day when you have had several successful reactions. The observations you need to make will  be clear after you have already seen them several times.
The alkaline reading
After the completion of the reaction, add 200 ml - 400 ml of water,  then boil for 5 minutes. This should result in a clear fluid with the RP settling to the bottom( a few aluminum potpies from soft drink cans, helps remove any excess iodine, when boiling).
Filter the RP out of the reaction mix, ,
Begin adding  base or a Sodium hydroxide solution.
Observation is the key, just watch what happens.
First the solution turns white when the lye hits it, then it clears ,
With more additions of lye the water layer  becomes milky white, and stays milky white for more than 30 seconds, you are very close to the alkaline pH level.

The milky white is what?? A white precipitate?? It can only be that which you are looking for.
Chili in the free base form, loosing its water solubility, coming out of the water layer

Mix it well and observe closely for the whiteness to go away a little bit, leaving the water layer cloudy
Add  another dose  NaOH, this puts it over the line, right where it needs to be
add your non-polar solvent.
You can be certain because
1. the chili was seen becoming non polar.
2. additions of NaOH do not form any added white precipitate in the water layer.
3. you may see a "lye lock", solidifying the water layer.

Wait a few minutes then test the pH of the water layer just to be certain it is over pH 12.4
Toss in some table salt if you wish.
 
 

Lye Lock
Watch out for a solidification of the lye/water layer (lye lock) too much solid material in the water lye , as it cools from the heat released by adding the NaOH, the NaOH begins to solidify. One good thing is you know the pH was high enough.
probably close to pH 13.7
Dilute it with warm water before it hardens, and begin draining out the lower layer, contine diluting, or it will harden then it is more difficult to keep dilute
keep it separated (don't shake)
Remove the lye solution

Washing the chili
After removing the lower water layer
Wash the non-polar/meth with about 1/2 volume  of  d-water
This means add water, shake fairly well, let it layer, and fully separate and remove the water layer
Repeat  the d-water wash three (3) times

Adding the HCl
Add an 1/2 volume  of  d-water again
Toss in a couple healthy  squirts of HCl.
A bit less HCl than is needed,  that will be 1 ml of 30%  HCl for each  gram of expected product
Shake well
allow to form into two layers
Separate and save   the water layer in your boiling bowl
Evaporate the water away
Enjoy the great crystal chili that pops out

then do another pull

Add more d-water to the non-polar/meth
Couple more squirts of HCl
shake well,
allow to layer
separate and evaporate

Continue in this fashion
Eventually you will get to  the last pull,
you will know it is the final pull because  a great deal of nasty HCl vapor will come off when  evaporating the mixture ,
You will have to wash the excess HCl out of  the crushed crystals, of this final pull,  with acetone.

All the pulls are the same and great chili even though the pH was at 10 , 9, 8 or 7 when the shit was dropped out of the non-polar.
WHY?
Most of it happened with in a small pH range of pH 10.0 to pH 8.5  As the chili takes on a   H+ attached  to its nitrogen,  it is capable of hydrogen bonding . Once it  accepts a Cl- ion,  it becomes suddenly  very water soluble.
It is related only partially to the pH because if you were very careful about any ions you could concievably maintain the freebase at pH 7.0 but the -OH  would interfere .
In this case it is the Cl- that is the primary factor affecting formation of the water soluble salt. That is why it is very important once you have the freebase form, to only use very pure distilled and deionized water to wash the freebase clean. because any negative ion , is going to cause a loss of product when washing the free base, depending upon the pH and a dozen different concentrations of whatever ions are present,

The pH will drop with each washing. The pH of pure water is 7.0, distilled is often 6.8 , tap water can be up to 8.5+

The less foreign ions present the better control you will have.
Better yields
Better dope
Considering the shitty quality of muriatic acid, it would be great to distill your own.
If you are consistantly getting dope that smokes burns dark and gakky , consider the source of your HCl probably also contains sulfuric acid, and you might consider gassing it  onstead or distill your HCl first.