I04 SOIL BACTERIOLOGY 



hydrochloric acid mixture against the silicate so that i c.c. 

 equals i c.c. 



5. In a similar manner standardize a solution of sulphuric 

 acid and phosphoric acid without the salts. 



6. The three acids should then be mixed. Approxi- 

 mately, I c.c. of the acid mixture will neutrahze i ex. of 

 the silicate mixture. 



Doryland, C J. T., Jour, of Bact , vol i, No. 2, pp 143-148, 1916. 



C. Partially Dialyzed 



1. Make a solution of sodium silicate as in the undialyzed 

 procedure. 



2. Mix with approximately normal hydrochloric acid, 

 making the mixture decidedly acid. 



3. Dialyze in running water, using parchment, animal 

 membrane, or collodion sacs until nearly all the chlorids 

 have disappeared. Make sure all the chlorids do not 

 dialyze out, or the mass will solidify. 



Note. — Collodion is conveniently prepared by dissolving soluble gun- 

 cotton in a mixture of equal parts of 95 per cent, alcohol and sulphuric ether. 

 Take about 5 grams of clean, white guncotton per 100 c.c. of fluid. It 

 requires at least twenty-four hours to completely dissolve the guncotton. 



Pour the collodion slowly into clean test-tubes and rotate. Try to 

 moisten the interior of the tube without forming air bubbles. The ex- 

 cess of collodion should be poured back into the bottle and the tube slowly 

 rotated in order to keep the interior of the tube covered with a uniform 

 layer. After pouring oJS the excess, stand the tube upright, mouth down, 

 on a sheet of clean paper to drain. Wipe off the excess of collodion from 

 about the mouth of the tube. Now rotate the tube for five minutes or 

 more with the mouth in a draft When dry, remove the sac by cutting 

 around mouth of tube and filling with water. Allow the collodion sacs to 

 stand in water until ready to use. 



Fill the sacs with the acid sodium silicate and tie the mouth with rubber 

 bands. When dialyzed, pour the silicate jelly out of the coljodion sacs 

 into a clean beaker and boil for one or two minutes over an open flame. 

 This should remove the absorbed air. 



