…Gunpowder for the Guns…

Fellow blogger Jim Schmidt authored a post, published yesterday on Civil War Monitor, regarding the importance of gunpowder and the war effort – particularly for the Federals.  As Jim noted, during the war there were more uses for gunpowder than just firing cannons!

His post, however gives me the opportunity to raise a few points about the “meal” which was fed to the cannons.  The mixture called gunpowder came from measured combinations of saltpeter, sulfur, and carbon – or saltpetre, sulphur, and charcoal in the period texts.  We know saltpeter better these days as potassium nitrate.  In the mixture, saltpeter provided the oxygen to sustain the fire against the fueling sulfur and carbon.  Sulfur also lowered the ignition temperature and increased the rate of combustion.

Mankind knew of gunpowder since at least the 9th century, providing ample time to experiment and perfect the recipe prior to 1861.  Generally the ratio was 65 to 80% saltpeter, 8 to 15% sulfur, and 10 to 18% carbon.  The ratios varied based on the intended use.  Slower burning powder used in rockets needed less saltpeter and more carbon.  Blasting powder required more fuel and far less saltpeter.   But for propelling shot and musket balls, the favored mix was around three-quarters saltpeter, with the remainder weighted more to carbon than sulfur.  The Ordnance Manual of 1861 notes variations in the mix between nations, and with different purposes:

As indicated, U.S. military specifications were 75-76% saltpeter, 14-15% charcoal, and 10% sulfur.  The specification came as an inheritance, somewhat, from English practice, but slightly altered by way of experimentation.

Another factor which effected the burn and combustion was the size of the powder grains.  I’ll save the detailed particulars for another date.  The short story is the Army specified the use of sieves to sort grains for particular uses:

  • Musket:  No. 1 and No. 2 between 0.03 and 0.06 inches
  • Mortar: No.2 and No. 3 between 0.06 and 0.10 inches
  • Cannon:  No. 4 and No. 5 between 0.25 and 0.35 inches
  • Mammoth: No. 6 and No. 7 between 0.6 and 0.9 inches.

The large columbiads used mammoth powder, which burned longer in the bore due to its larger size.  Ordnance officer Thomas Rodman conducted experiments on the eve of war to determine the best possible size grain for his heavy guns.  But much of the effort waited until after the war for application.

With such demanding specifications for gunpowder, the Army also provided methods for testing the quality of powder.  Inspectors looked for equally sized grains, using the sieves mentioned above, with angular appearance.  Good powder did not crush under finger pressure, and burned completely when fired on an open surface.

Beyond those “tests of the senses” inspectors might distill the components of a sample.  Saltpeter dissolved out with pure water.  Application of potash removed the sulfur.  Inspectors could weigh each to verify proper component mix levels.  Or more importantly, test for impurities.

Another test procedure, which was largely discontinued by the time of the Civil War, was to use a sample of powder in a test firing of an eprouvette such as this example on display at Fort Monroe:

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Eprouvette at Fort Monroe

Cast solid, the eprouvette had a fixed 45° elevation.  Using an exact measure of powder, the inspector observed the firing of a carefully weighed and measured solid shot.  The range attained by this shot would, in theory, give some gauge of the powder’s strength… in theory.

Problem was this theory of powder performance assumed the strength of propellant increased uniformly.  Further scientific tests determined this to be a false assumption.  Furthermore, the short bore of the eprouvette often prevented the large grained cannon and mammoth powder from fully burning.  And those large grains gave the most propelling strength when completely burned, as occurred in the longer bore of guns and howitzers.

A more accurate test, although requiring extensive setup, involved the suspension of a gun in a pendulum frame.  When fired, the movement of the gun gave some indication of the initial velocity of the shot.  While much more consistent than the eprouvette, such tests were only valid for the specific caliber of gun used in the tests.

By the time of the Civil War, even better procedures were at hand.  The Ordnance Manual of 1861 describes one such device – Major J.G. Benton’s electro-ballistic pendulum, derived from original work done by a Captain Navez of the Belgian Army.

Two battery powered electromagnet governed the movement of two separate pendulums.  The wires on the right of the drawing, paired with the electromagnets were leads connected to metal targets in the path of the cannon’s projectile, spaced at a measured interval.  When fired, the cannon’s shot hit the targets and broke the electric circuits thus stopping the pendulums.  The diagram below depicts the test apparatus configured for use.

The difference in time at which the pendulum arms stopped gave the measure of velocity.  Or at least that’s the ten-cent description of how it worked.  Gibbon’s Artillerist’s Manual of 1860 devoted about ten pages for a very elaborate description, so I refer readers there for the nauseating details.

High tech stuff for the 1860s.  And to think a functional electric toaster was still decades away!