AJ Hicks questions [OGD V6#370] the chemistry behind my recommendation of bleach as a virtually instantaneous sterilization agent. He cites the odor of chlorine in bleach as evidence of the volatility of hypochlorite. He is correct that the manufacture of bleach involves the uptake of gaseous chlorine by a very alkaline solution of lye but he got the chemistry wrong. Hypochlorite is generated by the following equation: Cl2 + 2OH- <---> ClO- + Cl- + H2O Although the equilibrium lies strongly to the right, there is always some free chlorine present, which accounts for its odor in bleach; if a small portion of the chlorine escapes as gas, the equilibrium compensates for this by shifting slightly to the left and supplying replacement elemental chlorine. Thus there is always an odor of chlorine coming from bleach without an appreciable portion of it escaping into the atmosphere. Therefore, as I originally stated, no confinement is necessary for bleach to be effective. Even my wife knows this when she does the laundry. The formation of hypochlorous acid at low pH is of no consequence since the pH of bleach is high, therefor the statement, "But if one were to drop the pH of the second solution..." is irrelevant. The sodium ion, Na+ has nothing to do with it! Yes, acidification could release a lot of chlorine gas, but this, too, is irrelevant since we do not normally add acid to bleach, nor can I figure out why we would ever want to do such a foolish and dangerous thing. I know how fast bleach reacts with cellular material, but the details of contradicting field tests are not given. Perhaps the bleach was too dilute, or perhaps the experimentor did not understand the need to conduct tests with reasonably fresh bleach, or perhaps his tests for live virus were contaminated by external sources of virus. If the experimentor did not understand the underlying principles of destruction of virus by bleach perhaps his technic was flawed. AJ repeats one of the most ridiculous myths of orchidology, namely that there is something mystical about TSP. I am surprised he didn't complete the myth by mentioning that undissolved crystals must be at the bottom of the container, otherwise the magic doesn't work. The antiviral activity of TSP arises from its extremely high pH. You can get the same results by adding 1 teaspoon of lye to a gallon of water. The statement by AJ that TSP is a more effective sterilizing agent than bleach is not even close to true. If the phosphate in TSP contributed to its sterilizing ability, why would we expose our precious orchids to phosphate in our fertilizers? Phosphate, like calcium, is not an "enemy" of orchid growth but a "friend." Virkon S is cited as a chlorine based disinfectant, but it is NOT chlorine or hypochlorite, which we are discussing. Table salt is also chlorine based, but has minimal toxicity unless we are prone to hypertension. A compendium of orchid viruses is included by AJ without explanation of what relevance it has for the effectiveness of bleach in destroying virus. I apologize for being so harsh in responding to AJ's criticisms, but I habitually crusade against myths of orchid culture that are repeated from one orchid grower to another with strong conviction, but are nevertheless without firm scientific support. Growing orchids properly is challenging enough without paying blind respect to these extraneous myths.
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