270 EXPERIMENT STATION RECORD. 



due to incomplete precipitation of the i)liosphoiic acid with the smaller 

 amonnts of magnesia mixtnre. 



Jt is believed tliat losses from the nseof only 2."> cc. of magnesia mix- 

 ture in ordinary fertilizer analysis are comparatively insignificant, 

 es])ecially Avhen i)hosi)hates rich in phosphoric acid are examined and 

 the precipitate is ignited in a Gooch crucible for only a short time. 



Further exi)eriments are reported which show that in order to get 

 uniform results when precigntating with 2.j cc, of magnesia mixture the 

 solution should be allowed to stand a few hours, with frequent vigorous 

 stirring. 



A method for the quantitative determination of water-soluble 

 phosphoric acid in superphosphates, W. Kalmann and K. Meis- 

 SELS {Choii. Zfg., is {1S!J4), Xo. JC, Ecpert., p. 180). — The method pro- 

 ])osed is based upon the difference in the behavior of solutions of 

 ])hosphates toward methyl orange and phenolpthalein as indicators. 

 Titiation with the former indicates one third of the acid present, and 

 with the latter the remaining two thirds. The method is carried out 

 as follows: 20 gm. of superphosphate is dissolved in 1 liter of water; 

 to 100 cc. of the filtrate methyl orange is added, and the solution 

 neutralized with half normal alkali. The same amount is titrated 

 with half normal alkali, using phenolpthalein as an indicator. The 

 amount of alkali required is designated a. Another 100 cc, of the 

 filtrate is measured into a 250 cc, fiask, a large excess of half normal 

 alkali added, and the flask filled to the mark, Aliquots (100 cc) of 

 this solution are titrated with half normal standard acid, using i^he- 

 nolpthalein and methyl orange as before. The amount of standard 

 alkali required nuilti])lied by 2.5 represents the amount required by 

 100 cc, of the original solution, and is designated h; the mean of a 

 and b multiplied by 0,0.355 gives the amount of phosphoric acid (P2O5) 

 in 100 cc. of tlie original solution (equal to 2 gin, of substance). 



On titration with Fehling's solution, and obtaining clear fil- 

 trates, H. Kral [Pharm. Centrfd Halle, 30, p. 411; ahs. in Chem. Centbl., 

 is<)i, JI, yo. 9. p. 44s). — The end of the reaction is recognized by acidu- 

 lating the filtrate from the titration and adding a little very finely 

 powdered potassium ferrocyanid. The smallest trace of copper is 

 shown by a red zone. The reaction with the powder is more sensitive 

 than with a concentrated solution of the potassium ferrocyanid. 

 Before filtering the author adds a little silica guhr {I'ielselyuhr) to the 

 filter, which prevents the slightest trace of cuprous oxid from passing 

 the filter. The use of silica guhr is also recommended in ])reparing 

 cloudy urine for i)()larizati()n in sugar determination. 



The determination of lecithin in plants, B, von Bitte {Ztschr. 

 physioJ. Chem., I'J, No. 4 and o, pp. 488-498). — From his studies on the 

 determination of lecithin the author concludes that oidy a part of the 

 lecithin is <liss()lved out when the material is extracted with ether and 

 then twice with alcohol, an hour each time. To determine the lecithin 



