Step 1] Cut your cactus up into small pieces, allowing them to dry completely. Once dry, either use a blender, mortar and pestle, or your method of choice to pulverize it into a fine powder.
Step 2] Place the cactus powder in Jar A. Slowly add the Isopropyl to the jar, doubling the volume.
Step 3] Turn the jar over gently 50 to 100 times in order to begin the extraction process (by avoiding vigorous shaking, you prevent an emulsion layer from forming). After the turning/mixing has been completed, allow the mixture to sit undisturbed until it has become greenish-black in color.
Step 4] Proceed to pour the mixture into Jar B, using coffee filters, tee-shirt, or cheese cloth to filter the liquid.
Step 5] Place the left-over solid contents (now strained of the alkaloid-containing alchohol into Jar B) back into Jar A, and repeat the initial steps, adding more Isopropyl to double the volume again. Repeat the further steps twice more, or until satisfied with the extraction. Each time, the color of the alchohol will be lighter green.
Step 6] Take the alkaloid-containing alchohol of Jar B, and slowly pour into a large glass/stainless steel pan for to allow for evaporation. This can be achieved by leaving a fan blowing over the pan, or allowing the pan to sit on a dish of boiling water. Be extremely careful, as the evaporating alchohol is extremely flamable.
Step 7] Once the alchohol has evaporated, a flaky black residue will be left over to be scraped up. You must be sure to smell the mixture, as you do not want any of the Isoprpyl to be contained in it whatsoever. It should have no alchoholic smell whatsoever. To be safe, you may wish to gently heat the mixture under 122 F for a while, to enure that all of the remnants have evaporated out of the flaky remains.
Step 8] Proceed to scrape the mixture up, which can then be ground up into a powder for consumption how you see fit.