This is my first posting to arch-theory so hello there every one. Now,
regarding testing for phosphate in the soil as evidence of blood/faecal
deposition, there are a few point I would like to make, but first a bit of
scene setting.
I did some phosphate analysis for the Watchfield dig (Christopher Scull et
al (1992) Archaeological Journal. Vol 149; pp 124-281) a Saxon burial site
with Iron Age settlement features.
The aim (one of them anyway) of doing the phosphate testing was to test the
feasibility of using a particular method in the field, one that is normally
done in the laboratory.
The method in question uses a 'single reagent' (Vanadomolybdate) with a
Lovibond Comparator. This method is widely used in the analysis of water
and agricultural products in conjunction with spectrophotometic assay.
Total Phosphate was extracted with dilute sulphuric acid (5%) and the
phosphate determined using Vanadomoybdate reagent available from British
Drug Houses (BDH) and a Lovibond Comparator 2000 (BDH) with a Phosphate disc
3/60 (BDH) calibrated in 10ppm steps. (0-100ppm).
As things turned out, I ended up doing most of the analysis back in the lab,
but I still think it could be done in the field.
Issues raised by this work are:
1. It is not the absolute quantity of phosphate that is important but
whether or not certain areas give statistically significant levels above
background.
2. Establishing the 'true' background level is key. This depends on how the
samples are treated prior to analysis as well as the 'spread' of soil types
in the vicinity.
A good deal of judgement is required as to the sampling strategy. Basically,
what is needed, is to show that the variance within and across soil samples
is narrow. So if one samples diverse soil types in the close vicinity of the
area suspected of having blood or faecal deposition, they should deliver
very similar mean values and variances within say (for arguments sake), one
standard deviation of the mean.
The total phosphate method described above is capable of accurately assaying
very low amounts of phosphate; there need not have to have been gallons of
blood spilt. A statistically significant difference can be shown if there
has been proper preperation of the samples - such as air drying and
sieving.
Of course, specific hypothesis such as the existence of
menstrual huts/seclusion rooms/birthing areas will not be advanced simply on
phosphate analysis alone.
Regards
David Webster
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|