NEPHELOMETRIC ESTIMATION OF PHOSPHORUS.
2373
the hypothesis of positive and liegative valences may possibly become a necessary adjunct t o the structure theory. This, as I have stated before,' must depend upon the extent of its applications and experimental verifications, and upon the part that is played by just criticisms in bringing t o light the relative merits and demerits of its applications. From these and the preceding points of view noted in this paper, the general criticisms and conclusions of Brunel have little, if any, bearing upon the electronic conception of positive and negative calences as a jormulative hypothesis. CINCINNATI, OHIO.
[FROMTHE HARRIMAN RESEARCHLABORATORY, ROOSEVELT HOSPITAL,NEW YORK, AND THE CHEMICAL DEPARTMENT, GOUCHER COLLEGE, BALTIMORE, MD.]
NEPHELOMETRIC ESTIMATION OF PHOSPHORUS. BY PHILIP ADOLPEKOBERAND G ~ T EGERER. R Received May 28, 1915.
TABLE OF CONTENTS.-I. Introduction. 11. Reagent. 111. Discussion. IV. Applications.
V. Summary.
I. Introduction. The estimation of phosphorus in biological and industrial sciences, especially of minute amounts, is becoming of increasing importan'ce A large number of volumetric and colorimetric methods have been proposed but thus far none has been satisfactory for micro-quantitative work. While looking for a suitable nephelometric precipitant2 for phosphorus in connection with our nuclease technic3 our attention was called4 to the reagent developed by Pouget and C h o u ~ h a k . ~This reagent consists of a nitric acid solution of strychnine and molybdic acid and produces a very sensitive reaction with phosphates (one milligram of phosphorus in 2 liters giving a very marked suspension of insoluble substance) similar in sensitiveness to the Nessler or the Gravesa reaction for ammonia. The authors found it will detect I part of phosphorus in 2 0 million parts THISJOURNAL, 37, 892 (1915).
* Uranium acetate and magnesia mixture were tried as nephelometric precipitants, but as preliminary experiments, especially with the latter, were not successful, these reagents were abandoned. 8 P. A. Kober and S. S. Graves, THISJOURNAL, 36, 1304 (1914). 4 Dr. I. Greenwald of this laboratory, after making an attempt t o apply this reagent directly for nephelometric work, abandoned it. Subsequently (see J . B i d . Chem., 21, 29 (1915)) he recommended the original reagent for a colorimeter method, although, according to him, the color of the opalescent liquid is so slight that it is not apparent until it is put into the instrument. It is obvious that any defect in the suspension for nephelometric work will make a defect for colorimetric, and our experiments, as indicated elsewhere, show that the reagent as recommended by the original authors, although usable, is not satisfactory. 6 Bull. SOC. chim., 5, 104 (1909); 9,649 (1911). 6 THISJOURNAL, 37, 1181 (1915).
2,371
PHILIP ADOLPH KOBER .4ND GRETE EGERER
of water. As the precipitate is slightly yellow and remains in suspension for a long time, the authors recommended it as a colorimetric reagent, but, practically, their estimations were turbidimetric, On studying the reaction carefully, w e found that ( ' 1 ) it was not constant and quantitative' and ( 2 ) the reagent gradually become yellow and deteriorated, probably because of tlie action of the nitric acid. Pouget and Chouchak realized this, as their directions state that the mixing of constituents must be made un1.v just before using. After making many variations of all cm~stituents,nci niaxked iini~r~)vtmient l*iiis obtaincti, hut on substilziting hydrociiloric j o y iiitric acid. the sol.iition mt only wnzained practically cuiuriess joi. t i t i indeJipiiie ieizptlr !:tit i m f , {vit WCLC .ifable*iincl gaz'e gmntitative and comtant i.e
d
One-tenth
\ulzitzon I(
a gram oi KI12P04is
o cc of this stock solution diluted to
I
.ndard \ohtion containing j mg. to a liter. 'i*v ;G cc of distilled water and j cc. of r> j S HCl, 1s. 5.' 1 1 1 . re,lgciit irc atlrlcti anti the solution shaken thoroughly. Ter? I c 1p l i o - ~ , ! ~ : i~~J i i t i o n1 ~ r . i r i ~ l a ror ~ i unknown) are then added slom71p , i i i i mixture 15 iliaken bv gentle rotation of the flask, and t c i ' btandrtig it 1s read.\. for reading in the nephelometrr.: :it' th. lizsi~i:mt.'yli -1s these directions h a w alreadv been given I L i - 110 necJ io1 repeating them here Results with New Reagent,- -As Pouget and Chouchak studied diffcrcnt d t s 011 their nitric acid reagent, the experiments i.cith. t h i i A t \ x ieciag~niv,erc Iiniited to pure d u t i o n s of mono-potassium phoiphati. i t 1 ierits oi liquid5 containing o, l . j , 4 c ) , 3.5, 3.0 and 2 . 5 tng. oi pI,wplia"t, respectivelv, precipitates were produced aq described 111 ilic dir?L i i : ~ nm~c i lx rc.dc!iiig\ plotted, as shown hplow. C u'\t 1 I:, I \,\a,riiade Septernkr r I , 1 9 1 4 ~with d reagent cont L i m i q ZltrcL \ >ociilini molj lxrate and Cur\ e B Wig. 2 ) was made May n i ~ i i reagent containing a preparation of our own sodium I - ~ r ~ l i ~ ~ ?on t t .paqe d 2375, t i
Solution of RHsPOh
I
0 cc sample contnined
lcIi.rnJ
v g
V R P
' 45rJ ~1 ?
'rXBLT: I Curve A
< I
13 92
0102j
14 95 rC, gu I 8 1', 19 00
n+ir
( 9
ooyrx
TjJ'
I)
iJ(>797
-7
r
j
.Iverage,
.. 1
--
Curve B
A_------.
Readings hIin
B
Readings Mm.
k
1.4
74
I j
92
0
24
17
25
0
23
0 21
19
00
0 22
0 21
20
90
0 22
0 21
2 3 00
0 0
29 23
-_
o 23
0 22
0
23
1 figures ~ represent the average of 2 to 3 readings upon two or three solutions of each concentration and the relatively large constant indicates that the reaction is practically complete. (See Discussion.)
111. Discussion. In ncphelornetric work published from the Harriman Laboratory thus Ear considerable stress has been laid on the position of the curws obtained i
NEPHELOMETRIC ESTIMATION OF PHOSPHORUS.
2377
from a gradationed series of known solutions. These suspensions represent such small amounts of material that no other technic can be conveniently employed to determine the completeness of precipitation, and so j a r we have relied only on the qosition of these curves, relative to the colorimetric curves, to tell us F tuhether the precipitation i s corn- z80 plete or not. As these curves are 72’0 very important for rapid and ac- 160 curate work, a recapitulation of 250 their meaning and use will not be out of place here. Taking Fig. I as an example, 230 when the standard solution, after 220 precipitation, was put on both ~ L Q sides of the instrument, the right side was set a t 15.0 mm. and when the light in the eye-piece was matched, the left side readfb0 13.92 (this reading, 13.92,is de- I7Q noted by ‘Is” in the nephelome- 4 . 0 tric formula and curve). Now, go leaving the standard solution‘ on the right set a t 15.0 mm., another solution (0.900 as strong as the13 -HcUios - standard) was put in place of the a y o m z s m n ~000797
