This is what Dr Loi says on another thread about using menthol crystals -
"First of all get a 5ml eyedropper bottle and fill it up with (at least half) menthol crystals which is available commercially at the pharmacy...and then filled it up to 5ml of homemade alcohol(mine made from rice..) or some people will use ethanol(white wine)...aloow the alcohol to dissolve the menthol crystals with occassional shaking of the bottle....once it is fully dissolved if left standing will separate into 2 layers...the top clear layer will be menthol liquid and the lower will be alcohol....but can only be used if it is mixed into a murky solution...now mixed it to e-liquids of your choice (my preference is Flue-cured tobacco and homemade Menthol at the ratio of 3:2)..."
http://www.e-cigarette-forum.com/forum/new-members-forum/2097-menthol-5.html
Thanks Kate. I'm going to try disolving it in warm e-juice instead of alcohol since it disolves in oil, alchohol, or warm water.
Brian