Chris_Halkides
Penultimate Amazing
- Joined
- Dec 8, 2009
- Messages
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Fabio Skoda
From a Kastle-Meyer procedure: "A positive reaction is indicated by the development of a pink colour within 5 seconds. Reactions occurring after 5 seconds, or before the addition of the hydrogen peroxide are inconclusive. A pink colour after phenolphthalein has been applied but before hydrogen peroxide has been applied normally indicates a false positive due to an oxidising agent being present. Rust could cause a false reading of this type." Therefore, they would have had to have been really fast with that sprayer.
LondonJohn,2) The pink colouration is almost certainly from a Kastle-Meyer test which is a presumptive test for blood. The test works like this: an area is sprayed with phenolphthalin, then with hydrogen peroxide. If blood is present, the phenolphthalin immediately oxidises to phenolphthalein, which is pink in colour. So an immediate pink colouration after applying the H2O2 over the phenolphthalin indicates the presence of blood.
3) HOWEVER, phenolphthalin + H2O2 will automatically oxidise due to the oxygen in the air within around 30 seconds, giving the same pink colouration even in the absence of any blood on the surface being tested.
4) Therefore, if the Kastle-Meyer test is positive for blood, any photos used as evidence must be taken within seconds of the H2O2 being applied to the surface being tested (which has previously been sprayed with phenolphthalin).
5) But...the sheer physical size of the cumulative areas in the photo shows conclusively that the pink colouration in the photo simply cannot be due solely to the presence of blood. For that to have been the case, the entire small bathroom would have had to have been sprayed down with H2O2 more-or-less simultaneously (perhaps by the use of some sort of large industrial sprayer), with the photo being taken within around 10 seconds of that happening.
6) This obviously didn't happen. In fact, it's more than likely that the bathroom was tested surface-by-surface using hand-held sprayers.
7) The inescapable conclusion, therefore, is that the photo of the small bathroom was taken long after each of the treated surfaces had reacted to the oxygen in the air, which oxidised the phenolphthalin to the pink phenolphthalein within 30 seconds.
From a Kastle-Meyer procedure: "A positive reaction is indicated by the development of a pink colour within 5 seconds. Reactions occurring after 5 seconds, or before the addition of the hydrogen peroxide are inconclusive. A pink colour after phenolphthalein has been applied but before hydrogen peroxide has been applied normally indicates a false positive due to an oxidising agent being present. Rust could cause a false reading of this type." Therefore, they would have had to have been really fast with that sprayer.
