August 11, 1916] 



SCIENCE 



215 



Feeding Experiments on the Nutritive Value of 

 Casein: E. M. K. Geiling and H. H. Mitchell. 

 Casein boiled for 2 hours is still able to maintain 

 adult mice for at least 50 days. Casein moistened 

 and heated in an autoclave for 1 hour at 15 lbs. 

 does not appear to lose its value for maintenance 

 of adult mice. Four mice were maintained for 70 

 days and 2 for 84 days on a ration containing this 

 product. Casein was digested with pancreatin and 

 then treated with 9.5 volumes 95 per cent, alcohol. 

 The filtrate, evaporated to dryness, was unable to 

 maintain mice for longer than 30 to 40 days. Mice 

 fed this product plus cystine returned to normal 

 weight and condition. Substitution of cystine by 

 flowers of sulfur had no beneficial effect. 



The Hydrogen Electrode Potentials of Phthalate, 

 Phosphate and Borate Buffer Mixtures: Wm. 

 Mansfield Clark and Herbert A. Lubs. 

 The hydrogen electrode potentials of M/20 solu- 

 tions of the following mixtures were measured at 

 20°. 



Acid potassium or the phthalate — Hydrochloric 

 Acid. 



Acid potassium or the phthalate — -Sodium Hy- 

 droxid. 



Acid potassium phosphate — Sodium Hydroxid. 



Boric acid and Kbl — Sodium Hydroxid. 



The solids crystallize beautifully and are all free 

 from water of crystallization. The acid potassium 

 phthalate, as shown by Dodge, is an excellent sub- 

 stance for the standardization of the sodium hy- 

 droxid solution. The sodium hydroxid may be 

 prepared sufficiently carbonate-free by a method 

 outlined and the hydrochloric acid may be purified 

 by distillation and is easily standardized. These 

 mixtures then form a convenient system of buffer 

 solutions to be used as standards in the color- 

 imeter method of determining hydrogen ion con- 

 centrations. 



Solutions of acid potassium phthalate alone have 

 a strong buffer effect. This combined with the ease 

 with which the substance can be prepared makes it 

 an excellent standard for hydrogen electrode meas- 

 urements. 



A Colorimetrio Method of Estimating Amylolytio 



Activity: Victor C. Myers. 



To 10 c.c. of 1 per cent, soluble starch solution 

 add 9 c.c. of water and 1 c.e. of a solution contain- 

 ing the amylolytic enzyme (ptyalin, amylopsin, 

 etc.). Digest at 38° C. At the end of some defi- 

 nite time, such as 30 min. (or appropriate inter- 

 vals), 1 c.c. of the solution is removed, at once 

 treated with 3 c.c. of saturated picric acid solution 

 and 1 c.c. of saturated sodium carbonate and then 



heated in a beaker of boiling water for 15 min- 

 utes. After cooling, the solution is diluted to 

 proper volume for comparison with a standard pic- 

 ramic acid solution in a colorimeter. Prom this 

 the sugar formation (maltose), and, therefore, the 

 amylolytic activity may readily be calculated. 



The Colorimetrio Determination of Glucose, Suc- 

 rose, Dextrin and Starch in Foodstuffs: V. C. 

 Myers and A. R. Rose. 



A portion of a saturated picric acid extract of a 

 2-5 g. sample (e. g., banana) is diluted with picric 

 acid solution, so as to contain about 0.02 per cent, 

 of soluble carbohydrates. Portions of 3 c.c. are 

 heated with 1 c.e. of saturated sodium carbonate at 

 100° C. for 15 minutes and the color which de- 

 velops matched against a standard solution of pi- 

 cramic acid. From the readings obtained and dilu- 

 tions used, the reducing sugars (glucose, frutose) 

 are readily calculated. Another 3 c.c. portion is 

 heated for 5 minutes at 100° C. before the carbon- 

 ate is added and then continued as above. This 

 portion gives the sum of the glucose (and frutose) 

 plus the inverted sucrose. Dextrin and starch are 

 similarly determined after hydrolysis. 



On the Citric Acid Production of Aspergillus 



Niger: James N. Currie. 



In a previous paper the author reported that 

 many cultures of black aspergillus produced citric 

 acid. Por the purpose of this discussion the acid 

 fermentation of this group of fungi may be con- 

 sidered as an oxidation process proceeding in three 

 phases which may be represented by the following 

 scheme : 



• oxalic acid — > car- 

 bon dioxide. 



Carbohydrate — » citric acid - 



Under optimum conditions of growth the chief 

 end product is carbon dioxide and only small 

 amounts of citric and oxalic acids accumulate. 

 Under restricted conditions of growth which may 

 be obtained on synthetic media large amounts of 

 free acids accumulate. Any one of fifteen cultures 

 studied can be made to produce both oxalic and 

 citric acids in various proportions, depending upon 

 the conditions of culture and the particular strain 

 of A. niger employed. 



The chief object has been to ascertain under 

 what conditions the largest yield of citric acid 

 could be obtained. The largest yields were ob- 

 tained on media to which calcium carbonate was 

 added. This may be due to the effect of maintain- 

 ing neutrality or at least a low hydrogen ion con- 

 centration in the media. Highest yields of cal- 

 cium citrate were obtained on the following media : 



