506 EXPERIMENT STATION RECORD. [Vol.40 



placed in sealed tubes and kept as a permanent scale of colors, which match 

 those produced by mixing equal volumes of a 0.02 per cent solution of bril- 

 liant green with gastric juice containing six different concentrations of free 

 hydrochloric acid (0.025 to 0.2 per cent). 



Accurate determination of soil nitrates by phenol disulphonic acid method, 

 H. A. Notes (Jour. Indus. n>ni Engin. Chem., 11 (1919), No. S, pp. 213-216). — 

 As a result of a study at the Indiana Experiment station of errors in the 

 colorimetric (phenol disulphonic add) method for determining soil citrates, 

 the following modified procedure is recommended: 



Th<- soil solution is prepared by Bhaking thoroughly 50 gm, of the soil with 



-in) cc. of distilled water and filtering several times through ;• g I grade of 



filter paper. Five cc ef the clear filtrate Is pipetted into small evaporating 



dishes and evaporated to dryness OH a steam hath. When cool, 1 CC. <>f the 



phenol disulphonic add solution, prepared according to Chamot, Pratt, and 

 Redfield i E. S. R., 26, p. 110), is added drop by drop to the dry residue, rotating 

 tiie dish so thai the add comes In contad with all the residue. After standing 

 15 minutes 15 cc. of cold distilled water is slowly added, after which by means 

 of a wash bottle ha\im; a fine jet. diiiiu i I t.. 8 per cent i ammonium hydroxid 

 la added until the yellow COlOX is permanent. The solution and a standard, 

 prepared from •"> cc. •<( a potassium nitrate solution containing 0D0O1 gm. of 

 nitrate per cubic centimeter and treated like the soils undergoing the t> 

 ate washed Into cylinders f«>r a Schreiner colorimeter, math- up t>> the phi nun. 

 mark, and compared in the colorimeter. 



Experimental data are given Indicating that the method m outlined is 

 adapted to the accurate determination of Boil nitrates in large as well as in 

 small amounts. 



The use of small ali<|tii>is of the water extract reduces the amounts "f Intcr- 

 fering salts, prevents beat reactions with the sulphuric add, and thereby 

 Increases the accuracy of the determination. Chloride found to have no 



effect on the determination. Calcium hydroxid was found to he the beat pre- 

 cipitant of colored water-soluble organic matter as well as of Interfering 

 Inorganic substances, Buch as soluble iron compounds. 



The solvent action of dilute citric and nitric acids on rock phosphate, 

 J. A. Siimi -. [Jour. Indus, and Engin. Chenu, it {1919), No. S, pp .— 



An investigation i^ reported from the Ohio Experiment station of the possible 

 value of dilute ( itrii and nitric add solution- a- substitutes for neutral ammo- 

 nium citrate solutions for determining the availability of phosphorus in rock 

 phosphate. 



Both acids were found to possess to,, high a Solvent power to discriminate 



between the available and oonavallable phosphorus. An additional objection 

 to thi> us*- of citric acid is that basldty has a deddedly depressing influen 

 on the solvent power, which can not he entirely overcome by the addition of an 

 extra amount of citric acid equivalent to the basldty. With nitric add, how. 



ever, it was found that the effect of basldty COUld Ik- wholly overcome by add- 

 ing exactly the amount of nitric add corresponding to the ha- ent 



The author concludes that while neutral ammonium citrate can not serve as 

 a means for measuring the absolute amount of available phosphorus, it preb- 

 ably gives ,i BUffidently reliable Indication of the available phosphorus of rock 

 phosphate and the changes In availability due to BUlfoflcatiOO and other 



processea The necessity, however, is pointed out of making two determina- 

 tions, one at the beginning and one at the end of the experiment, and of main- 

 taining absolutely uniform conditions. 



