798 



SCIENCE 



[N. S. Vol. XLIV. No. 1144 



Several samples of agar each claimed to be 

 the best that some commercial bouse has in 

 stock are secured. Powdered and shredded 

 agar are used alike. The shreds are cut up 

 into half-inch lengths, so that aliquots may be 

 more representative. (An ordinary print 

 trimmer makes a very satisfactory agar 

 cutter.) As many 500 c.c. Erlenmeyer flasks 

 (Jena, pyrex or non-sol glass) as there are 

 samples to be tested are cleaned, dried and 

 weighed to within 0.1 gm. 4.5 gm. of agar agar 

 are put in each flask and enough carbon diox- 

 ide free distilled water added to make the con- 

 tents of the flask up to 300 gm. The flasks 

 are shaken and put in a bath containing boil- 

 ing water. They are shaken at intervals to 

 aid solution of the agar. When the agar has 

 dissolved the flasks are removed and contents 

 brought up to original weight with hot carbon 

 dioxide free distilled water. 



25 gm. aliquots of the agar solutions thus 

 prepared are weighed out in triplicate intd 

 350 c.c. Erlenmeyer flasks (Jena, pyrex or 

 non-sol glass) which have just been rinsed with 

 hot carbon dioxide free distilled water. The 

 triplicates for each sample are designated for 

 convenience A, B, C — thus those from sample 

 No. 1 would be 1A, IB and 1C. 



To each A flask is added approximately 

 250 c.c. of hot carbon dioxide free distilled 

 water. The flasks are shaken until the con- 

 tents appear homogeneous. They are stoppered 

 and set to one side until they attain room 

 temperature. 



The B and C flasks are tightly stoppered by 

 cotton plugs and autoclaved for 15 minutes 

 under 15 pounds pressure. After autoclaving 

 about 250 c.c. hot carbon dioxide free distilled 

 water is added to the B and O flasks. The 

 B flasks are restoppered and left to cool to 

 ' room temperature. The C flasks are set on a 

 steam bath. When the contents of the 

 flasks are up to 95° C. or above, they are re- 

 moved individually and titrated at once with 

 N/10 or iV/20 carbon dioxide free alkali. One 

 drop of a 1 per cent, phenolpthalein solution 

 is used as the indicator. The titration is 

 finished when the faintest discernible, yet 

 permanent, pink color appears. The A and B 



flasks are titrated in the same manner after 

 they have cooled to room temperature. 



CURRENT YEAR'S TEST OF AGAR AGARS 



Seven samples of agar agar were secured in 

 answer to letters to five concerns. Five sam- 

 ples were shredded agar, one a powdered agar 

 and one, " Baeto Agar." Sample No. 1 in 

 the table is the powdered agar and No. 4 is 

 "Bacto Agar." 



All samples were uniform, clean and bright, 

 except No. 5, which was darker, dirty and 

 ununiform. 



TABLE I 



Acidity of Agar Agar Solutions and Nitrogen Con- 

 tent of Agars Used 



THE TABLE SHOWS 



1. That the maximum variation in acidity 

 between samples of agar agar when titrated at 

 room temperatures is only .024 per cent, be- 

 fore autoclaving, but is doubled by auto- 

 claving. 



2. Titrating the autoclaved aliquots when 

 hot accentuates the differences between sam- 

 ples, the maximum variation being greater 

 than the greatest acidity of the unautoclaved 

 aliquots. 



3. Sample No. 6 has the lowest acidity in 

 all cases. 



Sample No. 6 is the most stable because 

 autoclaving and heating change its reaction 

 least. H. A. Noyes 



PrjRDDE Agricultural Experiment Station, 



LaFayette, Indiana 

 3 E. T. = Room temperature. 

 A. = Autoclaved. 

 NA. = Not autoclaved. 

 H. = 95° C. or above. 

 (l)=No sample left for determination. 

 (a) 1.0;* = requirement of 1. c.c. normal acid per 

 100 c.c. 



