Argentine Artillery Officer and Friends, c. 1912.
The middle officer in the first photograph is the same man as third from left in the second picture. The flaming grenades on his uniform are traditional insignia for artillery, and in bothh these photos he appears to be sole representative of that branch. In the first photo two of the officers wear dark blue tunics trimmed with black tape. The third officer wears a white uniform for warm weather.
It's my supposition that company-grade officer rank is shown by the simple shoulder straps, while field-grade officers are distinguished by wider straps with room for rank pips. In the Argentine army, these pips were suns with a human face. The cockade on the caps would be light blue and white.
Page by Mark Conrad, 2010.