During a test in colloid and surface chemistry, students were asked to distinguish between two terms: orthokinetic and perikinetic coagulation.
The rate of aggregation is in general determined by the frequency of collisions and the probability of cohesion during collision.
- If the collisions are caused by Brownian motion, the process is called perikinetic aggregation;
- [If the collisions are caused] by hydrodynamic motions (e.g. convection or sedimentation), one may speak of orthokinetic aggregation.
from Everett, D. H. 'Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry'. Pure and Applied Chemistry, 2009, 31 (4), 577–638, p 610. doi: 10.1351/pac197231040577
Perhaps unsurprisigly, I got the terms mixed up, and used definitions the wrong way round. The problem was that nothing too obvious popped out when considering the prefixes and the respective processes.
- Question: To which meaning or association are the prefixes peri- and ortho- referring? The definitions are mostly clear. It is just that I would rather avoid memorisation, and would prefer to be able to always recall which is which based on the prefixes alone.
This means other meanings and etymology of peri- and ortho- are welcome, but will be considered off-topic on their own, unless a clear connection to the definitions of orthokinetic and perikinetic is provided. A short answer with an authoritative reference is very acceptable.