This article is from the Chemistry FAQ, by Bruce Hamilton B.Hamilton@irl.cri.nz with numerous contributions by others.
Generally, yes. Knowing why somebody is requesting information often helps
those considering responding to the request. It also helps to ensure that
responses will help solve the problem, rather than lead off on a tangent,
interesting though it may become. You should also indicate your level of
expertise, and where you have looked, as that prevents well-intentioned
people wasting time suggesting sources you have already tried.
If you require the information for a commercial or historical enterprise,
you should alway state that. The ability to download and edit information
is even more convenient than photocopying, and original copyright can easily
be inadvertently omitted. If you note that there may be a possible commercial
outcome, responders will try to ensure that the original source is fully
credited. A polite request to the copyright owner will usually result in
approval for your enterprise.
 
Continue to: