[Ger-Poland-Volhynia] Rengas Radzymin Warsaw Government, request for info

[Edith McKelvy]

A distant cousin-by-marriage who lives in Germany has recently found me on
the Internet!!! 
 
 Amazingly, her mother and my mother Olga Brade were childhood playmates in
Lesniakowizna, 15 miles east of Warsaw, almost 100 years ago.  Even more
amazing, she holds and has translated two documents, re my maternal
grandfather's land purchases of 1894 and 1903, from Russian to German
language for me (I use Google and/or Promt upon receipt to translate
German-English).
 
---   In 1894  " Excerpt...complete records of the mortgage book" of "the
seat RENGAS Radzymin Warsaw Government"
 
---    In 1903 (my grandfather) "Karl Brade had a passport which had been
issued in RENGAS on the 11.12.1901 under No. 49."
 
1.  What is RENGAS?  Is it a town -- a government agency -- a courthouse?
 
2.  I have read that passports were issued during this time period when
persons moved from one location to another.   I know that Karl Brade lived
in Lesniakowizna circa 1894, but where did he come FROM? 
 
Any assistance would be most appreciated...
 
Edith McKelvy
Silverdale WA