exceedingly low. This fact gives proof that the large quantity of calcium in 

 the water has its origin above all in an exchange of bases (a small part only 

 produced from solution of limestone). Then Ca>S0 4 , with (SO4) — > S. 



The amount of calcium by exchange of bases in water already saturated with 

 SO4 ought necessarily to cause a precipitation of CaS04 in the beds, decreasing 

 therefore the content of SO4 in the water and increasing that of calcium. 



When the exchange of bases is non-existent, or very weak, or indeed, when 

 it increases the calcium ions of the water against the sodium and magnesium 

 ions, the S0 4 content in milli-equivalents can be the same or even higher at the 

 point of saturation — hence the possibility of having Ca<S04. Theoretically, 

 an exchange of negative bases, in bringing about a decrease of calcium in the 

 water, can permit new solutions of SO4 and bring about, in consequence, SO4 

 above the point of saturation. But as these new solutions are from the CaS04, 

 there is then little chance that SO4 will be raised above the saturation point 

 unless the S0 4 can show MgS0 4 in solution or some other SO4. 



It has been observed frequently that water rich in S0 4 has a bearing on the 

 high Mg/Ca ratio. This fact should prove that water saturated with CaSO* 

 can then dissolve some MgS0 4 , which is very soluble, or some other magnesium 

 salt. In the Permian sands from the Itan-East Howard pool, Howard County, 

 Texas, and the North Cowden and Penwell pools in Ectoy County, Texas, this 

 condition is present. One water from the Cowden pool had saturations of 3 

 grams per liter of calcium, 34 grams per liter of magnesium and 27 grams per 

 liter of SO4. 



The tendency to saturation does not abolish the reduction of sulphates. 

 Hence, the water from the Carboniferous and from the Permian anticline of 

 Polasna-Krasnokamsk are very rich in H 2 S — so very rich, that it is difficult 

 to avoid the conclusion of the presence of a reduction of sulphates. It is simply 

 the question of a phenomenon of dynamics of the relative speed of the circulation 

 in solution of CaS04 from one part and of a reduction of sulphates of the other 

 part. In the Polasna-Krasnokamsk water, the speed of solution surpasses the 

 speed of reduction. When, on the contrary, the speed-of-reduction phenomenon 

 is greater than the speed of solution, the reduction deviates very perceptibly 

 and causes a very sharp decrease of SO4, which can even disappear. The weak 

 content of S0 4 or its absence have been observed for a long time in connate 

 water and considered as one of its exact characteristics. 



The reduction of sulphate in connate water brings, then, a considerable 

 decrease, or even a disappearance, of the ion SO4 and its replacement by the 

 ions S, S2O3, and SO3. Therefore, in some connate waters where SO4 is only 

 in very small quantity, or even absent, it is replaced by H 2 S, S, S2O3, and SO3. 



A few observations on the existing relation between the geological structure, 

 the petroleum pools, and the reduction of sulphates are available. 



259 



