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The brown soils of Gallura have been developed chiefly on granites whose formation dates back to Ercinic Orogenesis. These soils are characterized by little deep profiles, generally lower than 50 cm, well drained mainly because of small day contcnts (7.83 - 15.35%). The day distribution along the profile is rather uniform. The permanent charge of the inorganic colloidal fraction oscillates between 20 and 40 meq/100g, while the pH dependent charge is frequently higher than the permanent charge. The exchange complex of soil is chiefly calcium saturated. The base saturation percentage is rather low, varying between 0.30 and 0.58, but remains pratically constant along the profile; the small differences between the two horizons could be explained on the basis of the soils' sampling time rather than the basic cations leaching. Leached brown soils are also present in Gallura, but they very scarce. The organic matter of the soils rarely overcomes 7%, in the superficial horizons and decreases to values usually below the 3%. In the more typical brown soils the C/N ratio is below 14. The optical properties, the potentiometric and conductometric curves reveal a dose resemblance between the humic acids of these soils and those of Campeda andosoils.

A method is described for the separation by HPLC of two isomer phenols thymol and carvacrol. Satisfactory resu1ts have been obtained by using a chromatographic column μ Bondapak ,C18 and a solvent system constitued by acetonitrile (40%) and water (60%). The flow rate was 1,5 ml/min. The use of this technique permits determination and dosage of these two phenols in essential oils.

Four different extraction methods were compard, in oder to optimize the HPLC separation and quantitation of hydroxyphenols in «Thymus capitatus». One method was not suitable for HPLC ansly,is, whereas the others partially destroyed the hydroxyphenols extracted from the plant. The Charpentier-Cowles me thod was, found the most effective allowing to analyse, in spite of the losses, most of the free phenolic acids and of those bounded extractable in hot acidic medium but not in ethanol. For the phenolics in free form a method whith recoverier greater than those obtained with Hagerman Nicholson and Horvat-Senter methods was developed.