Dissolving cocoa in liquid
Commercial cocoa is frequently "dutched" or treated with alkalai, which increases the dispersibility of the powder. 

"The process darkens the cocoa ingredients, changes the taste by reducing bitterness, and increases the dispersability of cocoa powder for various applications such as beverages".

Source (paywall, sorry): https://www.ncbi.nlm.nih.gov/pubmed/18710243