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Powders	Solutions	Measurements	Data
The Powders	Preliminary	Specific Gravity	Specific Gravity
Powder Content	Oxalic	pH	pH
	Straight
	EDTA
	Balanced
	Summary

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The Powders

Comparisons were made of Ferric Oxalate (FO) powder from the following sources.

• Bostic & Sullivan (B&S), commercial supplier
• Artcraft (Artcraft), commercial supplier (planned to be added at future date).
• Vicente-M. Vizcay Castro (Vizcay), made by Vicente-M. Vizcay Castro following his preparation procedure
• Jeffrey D. Mathias (JDM), made following Vizcay's preparation procedure

 
 
 
 
 
 
 
 
 
 

The Solutions

Solutions were made from Ferric Oxalate (FO) powder as described.

Preliminary Solutions

Initially the B&S and Vizcay solutions were mixed as 16.20 grams FO and 48.0 ml H2O.  The solutions were shaken intermittently for 24 hours.  Due to the large amount of undissolved FO another 2.0 ml H2O was added.  After another 24 hours of intermittent shaking another 1.0 ml H2O was added.  It did not seem that the solutions would completely dissolve so they were shaken well and poured into a graduated cylinder and another 1.5 ml of H2O was added to bring the total volumes to 60.0 ml (at 78^oF).  These solutions are what this study refers to as the “Preliminary Solutions”.
It was noted that the Vizcay solution had what appeared to be about 4 times the undissolved FO as did the B&S solution.

Note:  If these solutions had dissolved completely, they would have been 27% solutions.

These solutions were shaken well and immediately divided into two 30 ml amounts.

For each FO, one of the 30 ml portions (Preliminary Solution) had the Specific Gravity (SG) and pH measured.

It was felt that Oxalic Acid may be necessary for complete dissolving.  For each FO, the remaining 30 ml portion had Oxalic Acid added until complete dissolving and are termed the "Oxalic Solutions".

Oxalic Solutions:

To these solutions (30  ml portions from above), Oxalic Acid was added in an amount of 0.10 gram at a time with shaking and waiting in between for dissolving.

The B&S and Vizcay Preliminary Solutions were found to dissolve completely when the following amounts of Oxalic Acid were added to 30 ml of solution.
B&S  0.50 g
Vizcay 1.40 g
These solutions are what this study refers to as the “Oxalic Solutions”.  The Specific Gravity (SG) and pH were measured.
 

 
 
 
 
 
 
 
 

Straight Solutions:

The remainder of the Preliminary Solutions after testing was 23.0 ml.  To this 0.50 ml of H2O was added and shaken intermittently for 24 hours.  The solutions were still not completely dissolved so another 0.50 ml H2O was added and shaken intermittently for 24 hours.  At this point both FO appeared to be completely dissolved at a temperature of 70^oF.  This solutions had a concentration between 26.4% (not dissolved) and 25.9%  (completely dissolved).

These solutions are what this study refers to as the "Straight Solutions".  The Specific Gravity (SG) and pH were measured.
 

 
 
 
 
 
 
 
 

EDTA solutions

John Melanson had claimed that EDTA (Na4) would allow the ferric oxalate solution to attain a higher concentration.  8 grams of ferric oxalate powder plus 1 gram of EDTA (Na4) had H₂O added in small increments until the material was completely dissolved at a temperature of 70^oF (allowing at least 24 hours of intermittent shaking).  The total H₂O added was 22 ml; the total volume of the solution was about 25ml.

These solutions are what this study refers to as the "EDTA Solutions".  The Specific Gravity (SG) and pH were measured.
 

 
 
 
 
 
 
 
 

Balanced Solutions

With the purpose of maximizing the ability to accurately compare powders, solutions were made from the Vizcay and B&S powders which had identical concentrations of ferric oxalate and identical concentrations of oxalic acid.  To accomplish this, the contents were estimated as discussed below  (see Estimated Contents of Powders).  An addition of 4% EDTA (Na4) was used to achieve FO concentrations of 30%.

8.45 grams B&S FO powder (contains 0.95 gram Oxalic Acid & 7.50 grams FO)
1.00 gram EDTA (Na4)
H₂O to make final volume of 25.0 ml
(However, an adjustment was made.)

It was noted that the solution made with B&S FO powder required more time to dissolve indicating that its oxalic acid content may be a bit lower than predicted.  This would predict the amount of Oxalic Acid to between 10.3% and 11.2% and the amount of FO to between 88.8% and 89.7%.  Because of this the Balanced Solution for B&S was adjusted by placing the FO content at 89.2% (Oxalic Acid content at 10.8%).  For the purpose of getting the solutions matched as close as practical, the solution was adjusted by:
adding 0.12 ml H₂O and
adding 0.04 gram Oxalic Acid
This resulted in a slightly adjusted solution as follows (it remains a 30% FO solution).

8.45 grams B&S FO powder (contains 0.91 gram Oxalic Acid & 7.54 grams FO)
1.00 gram EDTA (Na4)
0.04 gram Oxalic Acid
H₂O to make final volume of 25.12 ml

7.65 grams Vizcay FO powder (contains 0.15 gram Oxalic Acid & 7.50 grams FO)
1.00 gram EDTA (Na4)
0.80 gram Oxalic Acid
H₂O to make final volume of 25.0 ml

7.65 grams JDM FO powder (contains 0.15 gram Oxalic Acid & 7.50 grams FO)
1.00 gram EDTA (Na4)
0.80 gram Oxalic Acid
H₂O to make final volume of 25.0 ml

These solutions are what this study refers to as the "Balanced Solutions".  The Specific Gravity (SG) and pH were measured.

 
 
 

Summary of Solutions

Preliminary Solutions	16.20 grams Ferric Oxalate powder, plus 52.5 ml H2O Shaken well immediately before measuring (not dissolved, but assumed homogeneous).
Oxalic Solutions	16.20 grams Ferric Oxalate powder, plus 52.5 ml H2O, plus amount of Oxalic Acid needed to completely dissolve.
Straight Solutions	25.9 % solutions (FO powder only, no additional Oxalic Acid, assumes 100% pure FO),  Completely dissolved.
EDTA Solutions	8.00 grams Ferric Oxalate powder, plus 1.00 gram EDTA (Na4), plus 22 ml H2O, Completely dissolved.
Balanced Solutions	grams to make 30% solution of Ferric Oxalate using estimated contents of powders, plus 1.00 gram EDTA (Na4), plus amount of Oxalic Acid needed to provide identical minimum amounts in all solutions, plus H2O to make 25 ml when completely dissolved.

Estimated Contents of Powders

It can be assumed that the powders consist only of Ferric Oxalate and Oxalic Acid.  These are the only materials introduced in the Vizcay procedure, and these are the only ingredients claimed by Bostic & Sullivan in their product.  Trace amounts of Nitric Acid (detected by odor) and water are likely but assumed negligible.

The initial Oxalic Acid contained in the Vizcay powder can be estimated as follows.  The Vizcay preparation provides an additional 2.5% Oxalic Acid.  If it is assumed that all of this additional Oxalic Acid remains unreacted, the Vizcay powder contains:
1.92% Oxalic Acid by weight;
98.08% Ferric Oxalate by weight.
(% Oxalic Acid in powder) = (extra Oxalic Acid)/(powder produced which includes FO and the extra Oxalic Acid)
0.0192 = (117 * 0.025) / (149.7 + (117 * 0.025))

If one assumes that a certain amount of Oxalic Acid is responsible for the ability to completely dissolve the FO powders at a certain concentration (see Oxalic Solutions).     and the assumptions above, then it is possible to estimate the amount of oxalic acid in the batch of B&S powder.  For the following let:

B represent the solution made with B&S powder
V represent the solution made with Vizcay powder
F represent ferric oxalate
O represent oxalic acid included with the powder
A represent oxalic acid in addition to what was in the powder

The weight of powders used to make the Oxalic Solutions was identical, thus:

FB+OB = FV+OV

From the assumption above, the ratio of the total amount of oxalic acid to ferric oxalate in each solution is identical when the solutions just completely dissolve.  This is represented as:

(AB+OB) / FB = (AV+OV) / FV

What is desired is the amount of oxalic acid contained in the B&S powder (OB).  The following are known from the Oxalic Solutions and the calculation concerning the Vizcay powder above:

 

FB+OB = FV+OV	= 8.10 grams
AB	= 0.50 gram
AV	= 1.40 grams
OV	= 0.156 gram
FV	= 7.944 grams

OB is calculated from (derivation of equation):

OB = (FV * (AV+OV) + OV * (AV+OV) - AB * FV) /  (FV+AV+OV)

OB = (7.944*(1.4+.156)+.156*(1.4+.156)-.5*7.944) / (7.944+1.4+.156)

OB = 0.9086 gram

This means that the batch of B&S powder is thought to contain:
11.2% Oxalic Acid by weight;
88.8% Ferric Oxalate by weight.
(However, an adjustment was made.)

Note that the percentages may differ slightly as 0.1 gram of oxalic acid was added at a time for the determination of the Oxalic Solutions.  The material had not dissolved with AB = 0.40 and AV = 1.30

OB (low) = (7.944*(1.3+.156)+.156*(1.3+.156)-.5*7.944) / (7.944+1.3+.156)
OB (low) = 0.832
giving 10.3% Oxalic Acid
OB (high) = (7.944*(1.4+.156)+.156*(1.4+.156)-.4*7.944) / (7.944+1.4+.156)
OB (high) = 0.992
giving 12.2% Oxalic Acid

When the Balanced Solutions were mixed (see above), it was noted that the B&S powder may have less Oxalic Acid than at first calculated.  An adjustment was made resulting in that the batch of B&S powder is thought to contain:
10.8% Oxalic Acid by weight;
89.2% Ferric Oxalate by weight.

 
 
 
 
 

Measurements

Specific Gravity (SG) of Ferric Oxalate Solutions

Equipment:

• balance scale accurate to 0.01 grams
• beaker filled with water (large enough to completely submerge the small sample bottle)
• thin wire
• counter weight to zero scale (as needed)
• sample bottle with cap (small enough to be completely submerged in the water in the beaker)

The sample bottle is filled completely so that there is no air trapped inside.

If the bottle filled with water does not sink in water, then attach a “sinker” (lead) to the bottle for all measurements and consider this part of the bottle weight (the affect is a denser bottle, negative buoyancy).

The thin wire is tied to the sample bottle with the other end looped over the scale hook.

The wire is marked at the level of the water in the beaker when the sample bottle is completely submerged and not in contact with the beaker.  The wire above the mark is considered to contribute part of the tare weight along with the counter weight.  The wire below the mark is considered to be part of the sample bottle.
 

Procedure

• A)  The sample bottle is weighed
• B)  The sample bottle is filled with water and weighed submerged in the beaker with water
• C)  The sample bottle is filled with a solution and weighed
• D)  The sample bottle still filled with the solution is weighed submerged in the beaker with water
• The Specific Gravity is calculated as:  SG = (C-A) / [ (C-A)-(D-B) ]

Specific Gravity Results:
          temperature of 64^oF

Conversion of Specific Gravity into a Solution Concentration Percentage for FO

Page  58 of Dick Stevens' book, "Making Kallitypes" presents an abacus which relates the percent concentration of Ferric Oxalate solutions and specific gravity.  From this abacus, the following formula is derived.

                      %  = 157.89474(d-1)    (d = specific gravity)

Note that the Error is large due to the small volume used to measure the specific gravity.

% Concentration of Solutions Calculated from the Specific Gravity
Error of +- 7.9%

	B&S	Vizcay	JDM
Preliminary solutions	26.8	33.2
Oxalic Solutions	25.3	26.8
Straight Solutions	23.7	23.7
EDTA solutions		30.0
Balanced Solutions	30.0	31.6	28.4

With specific gravity measured more accurately (using a larger volume), the calculated concentration can provide a means to adjust the sensitizer solution to a desired percentage.  This may be attempted at a later time.

pH of Ferric Oxalate Solutions

Equipment:

• pH meter accurate to 0.1 pH with automatic temperature compensation and calibration.
• Shot glasses.  (Unless probe fits into bottle.)

pH Results:
     pH reference 7.01 measured as 7.0
     pH reference 4.01 measured as 4.0

pH of Solutions

	B&S	Vizcay	JDM
Preliminary solutions	0.4	0.7
Oxalic Solutions	0.6	0.7
Straight Solutions	0.7	1.0
EDTA solutions		0.8
Balanced Solutions	0.4	0.6	0.5

 

Print comparisons

Prints were made from all but the preliminary solutions.
Click here for Results.

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Derivation of the equation to determine amount of Oxalic Acid in the B&S powder:

(AB+OB) / FB = (AV+OV) / FV
FB = FV+OV-OB
(AB+OB) / (FV+OV-OB) = (AV+OV) / FV
(AB+OB) / (AV+OV) = (FV+OV-OB) / FV
AB / (AV+OV) + OB / (AV+OV) = FV / FV + OV / FV - OB / FV
OB / (AV+OV) + OB /FV = 1 + OV / FV - AB / (AV+OV)
OB * FV + OB * (AV+OV) =  (1 + OV / FV - AB / (AV+OV)) * FV * (AV+OV)
OB * (FV + (AV+OV)) = (1 + OV / FV - AB / (AV+OV)) * FV * (AV+OV)
OB * (FV+AV+OV) = FV * (AV+OV) + OV * (AV+OV) - AB * FV
OB = (FV * (AV+OV) + OV * (AV+OV) - AB * FV) /  (FV+AV+OV)