Deposits in Metastable Inorganic Hydrosols. 



35 



for organisms of the autoclaved parchment paper membrane. It is here to 

 be remembered that a stout parchment paper membrane such as was being 

 employed is less permeable than a Charaberland filter. It holds back 

 proteins and inorganic colloids, such, for example, as the silicic acid which it 

 is here being used to separate from the sodium chloride and excess of 

 hydrochloric acid. It is, however, impossible to be quite certain that no 

 chance infection occurred during the experiment, although the tubes did not 

 show any of the usual signs of bacterial invasion. 



DESCRIPTION OF PLATES. 

 Plate 2. 



Fig. 1. — Growths formed in Colloidal Solutions in Metastable Proportions of Colloidal 

 Silicic Acid and Colloidal Ferric Hydrate. Magnifications about 240 diameters. 



Fig. 2. — Different Views of Growths given by Metastable Admixture of Colloidal Ferric 

 Hydrate and Colloidal Sulphur a. The two colloidal solutions, after heating separately 

 to 120° C. for 10 minutes in the autoclave, were mixed in the ratio of 8 of colloidal 

 ferric hydrate solution to 2 of colloidal sulphur a, when the growths shown abov 

 appeared in a few minutes. Magnification about 240 diameters in each case. 



Plate 3. 



Fig. 3. — Coarser Growths and Fibres appearing in Solutions of Colloidal Silicic Acid only. 

 Figs. A, B, C, and D show more rapid growths produced by concentration due to 

 evaporation between slide and cover-slip. Figs. A and C under a magnification of 

 140 diameters. Figs. B and D under a magnification of 500 diameters. The fibres 

 in all four of these figures are the gel form of the diphasic system. Figs. E and F 

 are forms appearing spontaneously in sterilised and hermetically sealed test-tubes 

 containing colloidal silicic acid prepared aseptically from autoclaved ingredients, as 

 described in the text. The growths were obtained after 30 days' incubation in 

 the sealed tubes at room temperature. Magnifications for figs. E and F, 

 320 diameters. 



Fig. 4. — Finer Forms of Growth appearing in Colloidal Silicic Acid Solution, prepared 

 under aseptic conditions from autoclaved sodium silicate and hydrochloric acid, 

 and kept for 30 days in hermetically sealed glass tubes. Magnification about 

 240 diameters. These fine nodulated fibrils are very difficult objects to photograph 

 under the microscope, and the micro-photographs only give an idea of their appear- 

 ance, and fail to reproduce the beauty of the originals. 



