WITH PURE COLLOIDAL SILICA 79 



indefinitely in this condition. I ought to add that 

 I used a very pure sodium silicate and pure HC1 

 for its preparation, and that all the salts have been 

 dialysed away in a special dialyser with running 

 distilled water." 1 



As soon as it was obtained I made one of the 

 usual tentative experiments with it, making a guess 

 at the amount which it would be desirable to use 

 in the preparation of a colourless solution. I de- 

 cided upon ten drops of this dilute solution to the 

 ounce, using the other ingredients as before. This 

 yielded a faintly acid solution, and after boiling 

 it for ten minutes a minute amount of deposit was 

 produced. The flask was closed with a sterilised 

 rubber stopper, and placed on the north balcony. 

 After fifteen days the flask was opened and the 

 deposit examined, with the result that numerous 

 small Torulge single and in groups were found, 

 together with some Micrococci. 



This very speedy result surprised me, and I was 

 at once anxious to try some further experiments 



1 Dr. Rosenheim has since informed me that what he gave 

 me was some of a pure 0.01% solution of colloidal silica, the 

 materials for which were procured from C. F. Kahlbaum, 

 Chem. Fabrik, Berlin, whose agents here are Griffin and Sons, 

 Kingsway, London. I shall ask the Berlin firm to prepare a 

 0.1% solution, of which one drop would be equivalent to the 

 ten drops used by me for each fluid ounce of distilled water. 



