Explanatory Note 



The series embodies results of investigations, usually of 

 restricted scope, intended to aid or direct management or 

 utilization praotices and as gi.\ides for administrative or 

 legislative sctiono It is issued in limited quantities for the 

 official use of Federal, State or cooperating agencies and in 

 processed for-m for economy and to avoid delay in piihlicatione 



Y/ashington, D. C. 

 June 1950 



