1. The electrical conductivity of aqueous extracts of soils, in the proportion of one of soil to five of water, varies according to the time of extraction. In the more fertile soils extraction for three to four hours gives less than half as great a conductivity as is given in 4 to 11 days. 2. In peat the maximum value is reached almost at once, the extract having a high conductivity. The maximum value is also reached quickly in certain infertile soils, which give an extract of very low conductivity, closely similar to that of the purest upland streams. 3. A high electrical conductivity in the extract may only indicate the presence of an excess of salts, and does not necessarily indicate a good soil. It seems, however, that a rapid increase in conductivity as extraction is prolonged indicates increased solubility, partly through bacterial action and may be considered as a useful indication of fertility. A low conductivity, which remains low on continued extraction, denotes a soil so insoluble as to be unfertile.