I remember I read about some biology book where the average length of some kind of bird was specified as 30.48cm. In the same way I would guess that nobody measured the volume of Sulfuric Acid to four digits (and I'm not entirely sure how exactly one would do this anyway), but that instead some simple number was converted to a different system of measurements. Looking at the other rather odd amounts in the recipe would also suggest this theory.
There was a contributor to the BJ by the name Cyril Peckham. His formulas were rather curious in that he mixed metric units with English units (grains, scruples, etc) in the same formula. He would use whatever measure gave him a round number. His Amidol paper developer was said to be quite good.
A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.