Deposited from MetastaUe Solutions of Inorganic Colloids. 23 



in these experiments, there is obtained a mixture in common solution of 

 two metastable colloids, viz., ferric oxide and silicic oxide. These are the 

 favourable conditions for the deposit of the peculiar growths that have been 

 observed. 



The above solution, following Dr. Bastian, is called the " yellow " solution. 

 The colourless solution, which probably contained one metastable colloid 

 only, viz., silicic acid, was prepared, following again fairly closely Dr. Bastian's 

 directions. To 30 c.c. of distilled water 2 drops of the sodium silicate 

 solution were added, then 6 drops of " dilute phosphoric acid solution, 

 B.P." (Martindale), and a few crystals of ammonium phosphate (Martindale). 



Here, again, an alkaline silicate solution is taken which, with the phosphoric 

 acid solution, would yield at first a metastable colloidal solution of silicic acid, 

 and then with a greater excess a precipitate of silicic acid. The alkaline and 

 acid salts are just so balanced in the above proportions that only a small 

 proportion of the silicic acid is thrown out on autoclaving, <3r within a short 

 period of a few hours thereafter. 



Attention is drawn here to these important points in the chemistry of 

 inorganic colloids, because Dr. Bastian by long and patient experimenta- 

 tion appears to have arrived at the proportions most favourable to the 

 appearance of these growths. To the physical chemist it is obvious that 

 the proportions are just those which will give rise to a metastable solution 

 of a colloid, or a metastable mixture of colloids. 



It is under such conditions that slow deposition will take place and cyclic 

 variations can occur, if there be, during a long time interval, up-and-down 

 variations in physical factors of environment. Such are also the conditions 

 in a living cell, and hence the interest in the fact that so many of the 

 appearances shown by the growths are those seen in cell-products. 



In October, 1912, between the 18th and 24th, 48 tubes were prepared and 

 autoclaved as above described, the contents of the sets being as shown in the 

 following Table ; the qualities of reagent stated were added to 30 c.c. of 

 distilled water in each case. 



Thus there were a dozen tubes of each class, viz. one dozen " yellow " 

 solution, one dozen " colourless " solution, one dozen " yellow " solution plus 

 sodium carbonate, and one dozen " colourless " solution plus sodium carbonate. 



It may be said at once that the subsequent examination at a period of 

 seven months afterwards showed no observable difference in the growths, 

 either favouring or deterrent, due to the sodium carbonate. 



