46 LIFE: ITS NATURE AND ORIGIN 



state. He wrote: 8 "For the mineral forms of silicic acid, deposited 

 from water, such as flint, are often found to have passed, during 

 the geological ages of their existence, from the vitreous or colloidal 

 into the crystalline condition (H. Rose). The colloidal is, in fact, 

 a dynamical state, the crystalloidal being the statical condition." 



We now know that the basis of colloidality is degree of dispersion 

 (size or dimension of particulate units), and that many colloidal or 

 "amorphous" substances contain crystals or colloidal dimensions, 

 though non-crystalline aggregates may also be present. In the early 

 part of this century, P. P. von Weimarn showed that any substance may 

 be obtained either in the colloidal or the crystalline state, depending 

 on conditions of its formation. 9 Recently, rubber hydrocarbons and 

 viruses have been crystallized. The devitrification of glass by slow 

 crystallization may make it turbid and brittle, a condition sometimes 

 noticed in old chemical glassware and tubing. Professor Alexander 

 Silverman of the University of Pittsburgh kindly gave me a well- 

 developed crystalline globulite obtained from a tank of glass that had 

 cooled slowly when a factory suddenly shut down and was later aban- 

 doned. I have seen a similar globulite said to have been found in an 

 ancient Mesopotamian glass furnace. 



What may happen, if we wait long enough for results, is also 

 shown by the huge deposit of travertine (a calcareous rock), at 

 Mammoth Hot Springs, Yellowstone National Park, Wyoming. 

 Owing to the sudden release from solution and loss of carbon 

 dioxide, and assisted by the crystal-inhibiting action of the colloidal 

 algae which grow on the overflow surfaces, the freshly deposited 

 travertine has a filamentous or or cryptocrystalline structure. The 

 older deposits show increasing evidence of crystallinity, and in the 

 oldest deposits at the top of the terrace-hill, estimated by geologists 

 to have been laid down twenty to thirty thousand years ago, good- 

 sized, sparkling crystals are found, which still maintain the rhyth- 

 mic rings of the original deposit. 



Graham had remarked: "The formation of quartz crystals at low 

 temperature, of so frequent occurrence in nature, remains still a 

 mystery. I can only imagine that such crystals are formed at an 

 inconceivably slow rate, and from solutions of silicic acid which are 

 extremely dilute. Dilution no doubt weakens the colloidal char- 

 acter of substances, and may therefore allow their crystallizing 

 tendency to gain ground and develop itself, particularly where the 

 crystal, once formed, is completely insoluble, as with quartz." We 

 must consider, however, another mode of crystal formation, which, 



