ANALYTICAL EDI TIOX
54
Vol. 2, No. 1
free from COz and containing phenolphthalein. T h e solution remained colorless, showing that practically no Bas04 was decomposed to yield BaO.
ommended. Filtration shortly after precipitation in the case of iron is recommended.
Table X-Chloride
TEMPERATURE TIME
Contamination of Bas04 Precipitates Prepared under Varying Conditions CONDITIONS OF PRECIPITATION TABLE CHLORIDE Per cenl I1 0.15 Reverse &SO4 2 cc. HC1 I1 0.17 4 cc. HC1 8 cc. HCI
24-Hour digestion (4 cc. HCI) Acid divided N o digestion Excess BaClz
I1 I1
V V 5 cc. 10 cc. 15 cc. 20 cc. 1 minute 4 minutes 8 minutes HzSOa reverse HzSOa regular KzSO4 reverse KsSOa regular NazSOI reverse NazSOa regular (NHaIzSOa reverse (NHdrSOd regular Reverse Regular H a h n and O t t o .411en and Johnston Blasdale Fales
R a t e of addition of sulfate BaSOa from various sulfates
K ~ S O by I various methods
111 111 111 111
IV IV IV VI VI VI VI VI VI VI VI
IX IX
IX IX IX
IX
0.18 0.21 0.17 0.17 0.17 0.15 0.17 0.23 0.19 0.17 0.10 0.13 0.015 0.17 0.01 0.16 0.03 0.15 0.01 0 17 0.01 0.15
0.07 0 01 0.01
Loss of Bas04 Prepared under Varying
Table XI-Ignition
C. Hours 150 1 150 1 230 1 240 1 240 1 240 1 240 1 240 1 350 1 350 1 350 1 470 1 470 1 470 1 470 1 470 2 470 2 470 1 650 1 650 1 650 1 650 1 750 1 750 1 950 l'/r 950 1 950 1 Total Loss (54) Time (hours)
Conditions
REGULAR METHOD 0.1 0.1 0.3 0.0
...
-0.1 0.1 0.2 0.0
0.8 0.0 0.1 0.0
... ...
...
...
, . .
... ...
0.6 0.2 -0.1 0.4 0.3 0.1
REVERSE METHOD
...
0.8 0.2 -0.1 0.2 0.1 0.0
... ... ...
I . .
...
... ...
. . ,
1.3 0.2 0.0
2.6 0.2 0.0
...
. . ,
0.3 0.3 -0.3 -0.2 0.1 0.4 0.3 0.1 0.1 0.1 4.3 4.9 0.42 0.48 18.5
... ...
0.4 0.0 0.1 -0.1
...
0.2 0.1
.,
.
...
... ...
...
0.4 0.0
...
0.1
0.0
...
..,
... ... ... ...
0.2 0.6 0.1
0.8 0.4 0.0
... ..,
... ... ...
...
... ...
1.4 1.1 0.0 0 1 0 6 0.8 0.4 0 3 0.2 0.1 4.5 4.3 0.39 0.38 15.5
RECRYSTALLIZED FROM HISO, 0 4 0 0 17.7 0.4 0 4 0.0 1.0 0.8 13.5
... 1.9
0.8 0.0 16.2 0.4 0.5 5.0 0.8 -0.1 13.8
... ...
5.2 0.6 -0 9 1.0
0.8 -1.2 1 4 0 9 0,5 -0.4 -0.3 -0.2 -0.4 4.2 4.4 0.3 -0.5 0.3 -0.9 0.2 0.6 0.4 0.6 0.0 0.1 0.7 0.6 0.5 0.4 0.1 0.0 46.7 49.5 4.41 4 36 25.5
Conclusions
Acknowledgment
As a result of this study the following conditions are recommended for the estimation of sulfates: T o the nearly boiling barium solution containing 4-8 cc. of 3 N hydrochloric acid and 5 cc. excess of barium chloride (about 0.1 -11) add the sulfate solution dropwise (about 4 minutes) and with constant stirring. Digest 1 hour near the boiling point with occasional stirring. Wash the precipitate b y decantation, and, on the filter, with hot water until free from chlorides. The final weight of barium sulfate should not differ appreciably from 0.8 gram nor the final volume from 350 cc. Gooch crucibles may be used. Heating to 800" C. for 1 hour is rec-
Acknowledgment is made to B. E. Thomas for certain preliminary investigations in connection with this study. L i t e r a t u r e Cited (1) Allen a n d Johnston, J . A m . Chem. Soc., 32, 588 (1910). (2) Blasdale, "The Fundamentals of Quantitative Analysis," p 185, Van Xostrand, 1928. (3) Cornog, J. A m . Chem. Soc., 43, 2573 (1921). (4) Fales, "Inorganic Quantitative Analysis," p. 185, Century, 1925. (5) Foulk a n d Hollingsworth, J . A m . Chem. SOL.,46, 1220 (1923). (6) Hahn a n d Otto, Z . anorg allgem. Chem., 126, 25 (1923). (7) Hendrixson, J . A m . Chem. Soc., 37, 2352 (1915). (8) Hulet and Duschak, Z . anorg Chem., 40, 196 (1904).
An Improved Weight Buret' Harold B. F r i e d m a n arid Victor K. LaMer DEPARTMENT O F CHEMISTRY, COLCMBIA UNIVERSITY, h-zw YORK,hr. Y
AVIKG had frequent occasion to use a weight buret, the writers have developed the modification here described. It has the following advantages over the usual (Ripper) type with vertical protruding stopcock as in the early type of volume buret (Bur. Standards, Reprint 92) : (1) A horizontal stopcock like that in the ordinary volume buret, which makes manipulation and cleaning easier. (2) The guard which fits over the tip to prevent evaporation and mechanical loss while weighing is held by a ground joint to a fixed part of the buret, as contrasted with the attachment to the movable plug in the older type. This materially lessens the risk of breakage inherent in the older form. Thus, if the guard were not put on firmly it was likely to fall off and if pushed on too firmly the stopcock plug was likely to be forced out in the same operation, causing disastrous loss. (3) The knobs on the shoulders of the buret permit it t o be suspended vertically by a wire attachment from the balance arm, whereas in the older type it hung askew owing to the projecting stopcock.
A total volume of 60 cc., which is sufficient for three 20-cc. titrations with one filling and yet does not overload a balance I
Received August 16, 1929.
of Chemistry, Columbia University.
Contribution No. 612 from Department
of 100 grams capacity, has been found most convenient. It is desirable to hare the tip as fine as that on a standard volume buret to facilitate the delivery of small droplets, thereby increasing the precision with which the end point mag be determined when using concentrated reagents. It has been our experience that after the operator has become accustomed to carrying out weight titrations, which involves no more skill than weighing to a milligram on an analytical balance, the time consumed is but slightly more than that required by volume burets. The increased precision resulting from the ability to weigh to one more significant figure than it is possible to read a volume buret and the absence of such items as errors in drainage and unavoidable error in reading the meniscus are well worth this slight increase in effort. Furthermore, of course, a weight buret needs no calibration.
