This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
Mr. Stanislas Meunier communicates to Le Nature an account of some interesting specimens of globular calcareous matter, resembling pisolites or peastones both in appearance and structure, which were accidentally formed as follows: The Northern Railway Company, France, desiring to purify some calciferous water designed for use in steam boilers, hit upon the ingenious expedient of treating it with lime water whose concentration was calculated exactly from the amount of lime held in the liquid to be purified. The liquids were mixed in a vast reservoir, to which they were led by parallel pipes, and by which they were given a rapid eddying motion. The transformation of the bicarbonate into neutral carbonate of lime being thus effected with the accompaniment of a circling motion, the insoluble salt which precipitated, instead of being deposited in an amorphous state, hardened into globules, the sizes of which were strictly regulated by the velocity of the currents. Those that have been formed at one and the same operation are uniform, but those formed at different times vary greatly--their diameters varying by at least one millimeter to one and a half centimeters. The surface of the smaller globules is smooth, but that of the larger ones is rough. Even by the naked eye, it may be seen that both the large and small globules are formed of regularly superposed concentric layers. If an extremely thin section be made through one of them it is found that the number of layers is very great and that they are remarkably regular (A). By the microscope, it has been ascertained that each layer is about 0.007 of a millimeter in thickness.
On observing it under polarized light the calcareous substance is discovered to be everywhere crystallized, and this suggests the question whether the carbonate has here taken the form of aragonite or of calcite. Examination has shown it to be the latter. The density of the globules (2.58) is similar to that of ordinary varieties of calcite. It is probable that if the operation were to take place under the influence of heat, under the conditions above mentioned, aragonite would be formed. It is hardly necessary to dwell upon the possible geological applications of this mode of forming calcareous oolites and pisolites.