PRELIMINARY REPORT ON SYNTHETIC MEDIA 147 



tion of the chloride, sulphate and phosphate content of the 

 medium might be eliminated in some instances^ by adding the 

 organic acids in such quantities that the resulting organic salt 

 of sodium and of potassium should always contain equivalent 

 quantities of these bases. Such a procedure might, however, 

 give greater fluctuations in the osmotic action than the former 

 procedure. This question, with many others, must be left 

 for future investigators. 



For convenience there is given below a concise method for 

 making the ammonia-acetate-silicate medium and the ammonium 

 acetate solution. These figures give quantities of salts which 

 are only approximately inversely proportional to their osmotic 

 action. Up to the present time the writer has been unable to 

 secure all the necessary ionization constants. 



Weigh out: 8.40 grams of c.p. Na2Si03, 24.00 grams of c.p. 

 K2Si03 and dissolve in 500 cc. of distilled water. Dilute HCl 

 to a concentration so that 1 cc. of the silicate solutions does not 

 quite neutralize 1 cc. of the HCl. Add to the HCl 0.5 gram 

 of MgS04, 0.01 gram of CaO, 0.01 gram of Fe2S04 0.01 gram 

 of MgS04 and 1 gram of (NH4)2 SO4, and standardize the re- 

 sulting HCl solutions against the silicate, using methyl orange 

 as indicator, so that 1 cc. is equivalent to 1 cc. of the silicate 

 solution. 



Standardize a solution of H2SO4 in the same way, omitting 

 the salts. 



Standardize H3PO4 and CH3COOH in a similar manner 

 omitting the salts and using phenolphthalein as indicator. 



The acids may then be mixed in the following proportion: 



HCl 153^5 



CH3COOH 153.5 



H2SO4 77.0 



H3PO4 116.0 



One cubic centimeter of this acid mixture will just neutralize 

 1 cc. of the silicate mixture, using phenolphthalein. 



* Acids whose solubility in water is so low that solutions, equivalent to the 

 silicate solution, cannot be obtained will still further complicate the question. 



