Patent classification systems are designed for classifying and retrieving technical subject matter such as patents. They are similar to library classification systems like Dewey and Library of Congress.
The top level of the CPC scheme is Section. There are 8 sections: A – Human Necessities, B – Operations & Transporting, C – Chemistry & Metallurgy, D – Textiles, E – Fixed Constructions, F – Mechanical Engineering, G – Physics, and H – Electricity.
US patent # 13/840,818 "Degradable polymers and method for fracking applications" has this classification: C09K8/68.
C = Chemistry & Metallurgy
C 09 K = Materials for Miscellaneous Applications, not provided for elsewhere
C 09 K 8 = Compositions for drilling of boreholes or wells
C 09 K 8/68 = ...containing organic compounds