DETERMINATION OF PHOSPHORIC ACID.
282
This f o r n i of funnel is known as the Hirsch funnel.' As in all cases the results were nearly i d e n t i c a l ; i t is e v i d e r r t that the d i f f e r e n t methods of w a s h i n g the p r e c i p i t a t e had no i n f l u e n c e upon the result. Exactly twenty-three molecules of Na,O are required for one niolrculc of P,>O,. The standard acid is prepared b y d i l u t i n g 323.7 cubic centinieters of i i o r n i a l s u l p h u r i c a c i d to one liter, and not 3 2 6 . j cubic centimeters as prev i o u s l y stated. The a l k a l i s o l u t i o n , after reiiiovilig carbon d i o x i d e by b a r i u m hydroxide, i s brought to the saiiie strength a s the a c i d , volume for volume. One c u b i c centimeter of either solution is then equal to one n i i l l i g r a n i of P,O,. P A I r , A D E r ~ m f I , \ . PA.,February 20.
rXgq,
NOTE ON PEnBERTON'S IlETHOD OF PHOSPHORIC ACID DETERMINATION A S COMPARED WITH THE OFFICIAL METHODS.* BY W.M. C . D A Y A N D A . p. B R Y A N T .
H
A V I S G o c c a s i o n to make a series of determinations of phosphoric acid in Florida phosphate r o c k , we have used the method recently described by Mr. H. P e m b e r t o n , J r . %and incidentally have made a number of comparisons between it and the o f f i c i a l method. The following are the r e s u l t s : ( ; K A V I M E T K I C DETERMINATIOXS.
No.
I.
Mg,P,O1 No. I . Mg,P,O, No. 2. No. 3. No. 3. No. 4.
From 0.7867 gram Na,HPO,f From
I.IIOO
1213~0,obtained 0.2426 gram
grams Ka,HPO, -k xzH,O, obtained 0.3433 gram
From 1.0000 gram Florida rock, obtained 0.j 8 2 8 gram From 0.3807 grani Florida rock, obtained 0.0262 gram From 0.4831 gram Florida rock, obtained 0.0333 gram From 1 . ~ 3 grams 6 Florida rocki obtained 0.0227 grani
Mg,P,O1 Mg,P,O, Mg,P,O, Mg,P,Ol
1 To be had from Bullock and Crenshaw, Philadelphia. A disk of filter paper of the diameter of an American silver quarter dollar (fifteen-sixteenths inch) is used. when employiiig the smallest size funnel. I can highly recommend this f u n n e l in all cases in which the precipitate is to be titrated. The precipitate presents a perfectly flat surface. is easily atid quickly washed, and is readily transferred with the aid of the wash bottle to the beaker. The funnel can be employed only when using the suction p u m p , hut it has the advantage of not requiring a platinum cone, and the size of t h e filter is reduced
to a minimum. 2 Read a t the stated meeting of the Chemical Section, of the Franklin Institute held February
20,
1€94.
283
EXAMISATION OF P O R T L A N D CEMENT. DETERYIN.%l'IOSS BY PEJIBERTOS'S METHOD.
No. I used 1.0737 grams Na,HPO,+ 12H,O and 22.88 cubic centimeters K O H solution and 1.85 cubic centimeters acid. No. I used 1.0370 grams Na,HPO, rzH,O and 21.30 cubic centimeters KOH solution and 0.80 cubic centimeter acid. No. 2 used 1.oo00 gram Florida rock and 41.85 cubic centimeters KOH and 5.05 cubic ceiitinieters acid. No. 3 used 1.oo00 gram Florida rock and 7.55 cubic centimeters KOH and 3.10 cubic centimeters acid. No. 4 used I .ooooFlorida rock and 6.75 cubic centimeters KOH and 5.50 cubic centimeters acid. Strength of H,SO, used I cubic centimeter = 0.015998 gram H,SO,. Strength of potassiuni hydroxide solutiou I cubic centimeter=o.o1847 KOH.
+
T h e percentages of P,O,, calculated from the foregoing determinations, are : Gravimetric. Pembertou.
Sitbstaiice.
sodium hydrogen phosphate.. S o . I , sodium hydrogen phosphate.. s o . 2 , Floridarock No. 3, Florida rock.. KO.3, Florida rock.. No. 4, Florida rock.. No.
I,
.......... 19.72 .......... '9.78
............................ .......................... ..........................
37.28
..........................
4.40 4.41 1.45
19.73 19.99 37.22 4.53
...
I .32
It is evident from the above figures that the agreement betweeii the results of the two methods is as close as could be desired. Inasmuch as the Pemberton method is of extreme accuracy, is very easily carried out and effects a great saving of time and labor over the official method, it is well worthy of extended use. W e have found that the author's statement of the time required for a single deterinination, naniely, thirty to forty minutes from the tinie the solution is measured out for titration, is entirely reasonable. Oniitting filtration of silica makes no difference i n the accuracy of the results. SWARTHDIORE COLLEGE,PA., February 10, 1894.
THE CHE171CAL AND PHYSICAL EXAlllNATION OF PORTLAND CEnENT. (Confintrcd from pace 273.) B Y THOMASB . STILLMAN; PH.D.
REFERENCES (1870
to 1892).
1870.
American Chemist.-Chemical examination of a piece of cement metamorphosed while immersed in t h e water of Bayen de Luchon, 148.
