[Ger-Poland-Volhynia] Military ranks .. pre 1917

[Elmer]

Hello 

Several of my Grenke ancestors served in the Czar'a army . Is there a way that i could determine what their rank was. 
I some how think that ethnis Germans would be given a commissioned officers rank . Also , would it be possible to determine what corps they were in ie , infantry , artillery or service type of corps

Any thoughts would be appreciated 

Elmer Grenke