Polecat, the answer is YES. Ever wonder about that line " . . . and the rocket's red glare . . ." when all the powder flashes you have seen were orange? 19th century guys used a more pure grade of saltpeter than used today, at least in the USA. The best American powder of that period was made in Augusta, Georgia. Allegedly du Pont made sure that mill ceased to function after April, 1865. Augusta made better powder than did that mill on the Brandywine.
Got it! But, were the powders back then less effected by humidity than what we use today? Or less....?
Depends on the time period in question and who made the powders.
Another point here is relative to "what we use today".
If you look at GOEX made between 1972 and 2000 you see a black powder that was considerably more hygroscopic than old powders. They used a poor grade of potassium nitrate that contained some sodium nitrate.
High purity potassium nitrate is only very mildly sensitive to moisture in the air. How the powder behaves with changes in relative humidity is going to depend on how pure it is. A 99.9% pure potassium nitrate picks up only minute amounts of water from the air until the relative humidity reaches 92%. That is it's critical point. At 92% R.H. it begins to pick up moisture from the air. At 100% it should only pick up 1.6%, by weight, of water from the air. C&H once used that weight increase at 92% R.H. as a QC test on their potassium nitrate supply. With the old GOEX made with the Vicksburg Chemical Company potassium nitrate the total weight increase at 99 to 100% R.H. was 16%, not 1.6%.
The powders we have now at this time are all made with a high purity potassium nitrate and are not noted for getting very damp when exposed to humid air.
