40 JOSHUA ROSETT 



METHOD AND OBSERVATIONS 



The conmiercial solution of sodium silicate (specific gravity 

 about 1 : 40) is mixed with a watery solution of sodium salicylate 

 (concentration about 1:10), one volume of the salicylate solu- 

 tion to from ten to twenty volumes of the silicate solution; the 

 solutions should be mixed gradually to prevent the formation of 

 a coagulum. Fragments of potassimn permanganate are dropped 

 into the mixture thus formed, and the osmotic growth begins. 



As soon as the fragment of KMn04 comes in contact with 

 the liquid medium, some of the salt of course passes into solu- 

 tion. This solution is acted on by the medium and a precipi- 

 tate (probably the oxides of manganese and sihca) is formed 

 around the fragment of the salt. This precipitate forms as 

 a rather rigid layer or membrane, which constitutes the initial 

 osmotic sac, and which bars the entrance of both the silicate 

 and salicylate but allows the entrance of water. The exact 

 nature of the chemical reactions by which this first membrane 

 is formed and by which subsequent growth is accomphshed h3,s 

 not been worked out, but the first step appears to be a reduction 

 of the KMn04 so as to give manganese oxides and probably 

 silica compounds. The action of the salicylate is not clear; 

 it may be catalytic. 



As water enters the sac, on account of the osmotic action of 

 the saturated KMn04 solution within, additional quantities 

 of the salt pass into solution. As long, therefore, as there re- 

 mains a supply of undissolved KMn04 there can be no relief of 

 the osmotic pressure, and the sac expands. Within a period 

 of less than a second it becomes about a third larger than the origi- 

 nal salt fragment (see fig. 1, A). The smaller sacs are either 

 ovoid or spherical; the larger sacs are more nearly of the shape 

 of the original crystal, but with rounded angles. The solution 

 outside of the sac being of a higher specific gravity than that 

 within it, the highest point of the sac becomes the point of least 

 resistance, and the sac, having expanded to its full capacity, 

 bursts open at this highest point. Through the rupture a 

 stream of KMn04 solution pours forth and comes in direct con- 



