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Of real interest is the conclusion that formic is better in low light but the normal acetic is better (faster) in bright light. He states that a mixture of both is best of all.

the developer I've been using all along is the one below but it has 10ml acetic. I'm gonna change it to 8ml formic + 2ml Acetic and see what happens.

355ml Distilled water
15g Ferrous Sulfate
8ml Formic acid
2ml Glacial acetic acid
20ml 190 proof grain alcohol  
20g sugar


Well I'll be...it works.
First test was to see if it will actually develop and it did.
I exposed for 30s in full shadow at 6:30 at night, f/8 and about 1.5 bellows draw. I was impressed by how quick it came up and it was clearly over exposed. I then did the same 30s with a vinegar developer and it took significantly longer but it was a good exposure combination.
So I went back and did the formic at 5s. Yea I pushed that a bit. It needed about 10-12s I'd say and that was an increasing loss of light.

I'll see how it goes from here but it looks like it will lower exposure times quite a bit. Let's just say about half, as an off the cuff, non scientific quess.

Sounds interesting. What does it do to the color of the plate? Do positives come out coffee and cream or gray/silver?

Here is a scan with the same adjustments made. I feel like it's not a good example because the formic plate is very over exposed so we can't see it's potential when properly exposed. However, it does show the difference of development with the same amount of exposure (30sec).
Top is the formic, bottom is the vinegar/acetic.
Bob, it;s kind of hard to say because the formic is way over exposed and it seems to have effected the tone. I'll do a better test. Hopefully today or tomorrow.

Also of interest was how the author in the first entry explained the development:
"The image flashed out rapidly and in less than a minute was completely developed, the result being clean and brilliant without the slightest trace of fog."

So...reading into that statement it can be implied that their normal development was >1 minute. Did these guys use a lot less exposure than us and therefore develop for longer times?

Ok, did another test and it doesn't seem that much faster but maybe a little. It's definitely different though. The way it comes out of development is different. The formic came in quicker with and then quite gradual. The acetic/vinegar hesitated then came in pretty quickly.
I kept all parameters the same as best I could.
This was in shade at f/8 11am, 10sec exposure. I had a clock to see how many seconds development was and tried to stop at the same point (I was looking at his eyes). It was 15s for the formic (top one) and 20s for the bottom one (vinegar). The results show that I probably should have done 15s for the vinegar as well.
Looking at an angle the density is much better for the formic. Look around the plates and you see difference in contrast and exposure. The vinegar developer (unfortunately not my normal dev) has that weird area that looks over exposed.
Anyway, I'm not sure what to do with this. It's completely usable but I don't know if there is a gain. In this instance I'd take the formic over the vinegar.
In those papers it sounded like the formic was better in low light. I'd say you can definitely see a difference in density. So perhaps you can get a better looking plate in low light with formic. Probably a little gain in exposure. I had done formic at 5 sec and felt it was a bit underexposed but stopped development probably at 20sec. Perhaps formic prevails with shorter exposure and longer development?
I went ahead and scanned the five second exposure with formic. I probably could have developed longer and got a similar result. a bit odd exposure on the right side.