While most of the reports were satisfactory a number of minor errors were rather too common and I deal with them below.

1. Several reports ommitted to include a list of the species of seaweed collected .

2. There were some unusual figures for the dry weight yield which were attributable to using the dry weight of the small sample taken for oven drying as the total dry weight of the extracted seaweed. The dry weight obtained from the small sample should be used to calculate the dry matter content of the larger sample used for extraction , as most of you did correctly.

3. There were some bizarre comments on the difference between fresh weight and dry weight yields being due to the greater ease of extraction of alginates from dried seaweed. In the fact the opposite is usually the case but this is not what we tried. In our experiment we only performed an extraction from a fresh weed sample. The difference in yield is simply due to the water content of the fresh material. Most biological materials have high and variable water contents so that fresh weight is not a reliable indicator of the quantity of biomass present, therefore one invariably uses the dry weight.

4. Major problems with viscosity. Most of you plotted shear rate on the x axis and viscosity on the y axis. On such a plot a Newtonian fluid would give a horizontal straight line since the viscosity is constant and does not change at different shear rates. Many of your samples showed an increase in viscosity with shear rate, this is dilatant behaviour though most of you called it pseudoplastic. I think the confusion arises through comparison with a plot of shear stress against shear rate. For a Newtonian fluid viscosity=shear stress/shear rate and will therefore give a diagonal straight line. But what you were plotting is a completely diffreent graph of viscosity against shear rate which not unsurprisingly gives a different line. Some of you did point out that we should expect to see pseudoplastic behaviour though found dilatant. I think only one group actually recorded pseudoplastic behaviour. Possibly the dilatant behaviour could have been a consequence of the incomplete removal of Ca ions leaving regions of partial gel structure which would act as particles and give dilatant type behaviour.

Dr. L. Ramsden, Botany, 26/4/99