STARCH AGAR 115 



color disappears; add a slight excess of acid, shake thor- 

 oughly, and allow to stand a few minutes. The finely 

 precipitated cellulose will rise to the top, due to the large 

 quantity of free hydrogen hberated in the precipitation 

 process. Shake the solution vigorously at intervals of a 

 few minutes to dislodge the hydrogen. As soon as the 

 free hydrogen has escaped the cellulose will settle rapidly. 



3. Wash through repeated changes of water untill free 

 from copper and chlorin. After the washing is complete, 

 bring the cellulose in the solution up to 0.5 per cent, by 

 allowing to settle a few days, and siphoning off the clear 

 solution or by evaporating. Add the nutrient salts desired, 

 together with i per cent, of thoroughly washed agar; heat 

 in autoclave or boil until the agar is dissolved; tube and 

 sterilize in the usual way. 



McBeth, I. G., Soil Science, vol. i, No. 5, pp. 43S, 439> 1916. 



Medium 54 

 Starch Agar 



(a) Agar • .10 gni. 



(Salts the same as for Cellulose Agar, Medium 52.) 

 Tap-water Soo c.c. 



(b) Starch solution 500 c.c. 



To 10 grams of potato starch suspended in a little cold 

 water add 800 c.c. of boiling water. Concentrate by 

 boiling to 500 c.c. This breaks up the starch grains and 

 should give a nearly transparent starch solution. 



