The Sergeant:  It is difficult to draw the line between the duties of the corporal and those of the sergeant.  There is really no great difference in their duties.  Sergeants generally have larger details under their charge, and have corporals under their direction to assist them.  They are usually entrusted with more responsible duties, and they are supposed to have greater experience, and to approach nearer the commissioned officer in a knowledge of all military matters.

Sergeants generally have a more general supervision of the men, whilst corporals have more of the detail to attend to.  The company should be divided into a number of squads proportionate to the number of duty-sergeants in the company, with a proportionate number of corporals, who should have charge when the sergeants are absent.

They are responsible for the camp and garrison equipage which the squad has in general use.  They have charge of the preliminary instruction of the men in their various duties, and must preserve order in their squad, and see that the men do not absent themselves without proper authority.  

(From August V Kautz, The 1865 Customs of Service for Non-Commissioned Officers and Soldiers--A Handbook for the Rank and file of the Army)