I,VD USTRIAL A S D ESGINEERI-VG CHE.1fISTRY
972
currents produced a beneficial stirring effect, which was much more pronounced than with single-phase operation.
Vol. 17,
KO.9
from the sizing being saved for use in making another batch of the same composition. Water
Procedure
In making a batch of catalyst, the proper proportions of iron oxide and the desired promoter (14 mesh or even smaller)
-2iL
A-ote-Iron oxide suitable for the manufacture of ammonia catalysts may be prepared by burning pure iron Iron rods (‘/4 t o 3/a inch) have been found to burn readily in d curent of oxygen.
Rere first weighed out and thoroughly mixed on a clean iron plate. The mixed batch was then shoveled into the furnace and the electrodes spaced and inserted a few inches into the batch. The material was hollowed out in the center and heaped around the edges so that the melt would stay in the center. Water was started running through the electrodes and the power switched on a t the maximum voltage. The three electrodes were then connected with a narrow bridge of hot oxide. When the maximum allowable current a t the starting voltage had been reached the next lower voltage was applied. This was repeated until the lowest voltage, highest current tap was reached (9-25”, 4O0Oa,3-phase). When the oxide included between the electrodes became fluid the power was shut off. After the mass had cooled the electrodes were withdrawn and the fused oxide crushed and sized, the fines
Elec+rode
Figure 3-Main
Electrode
Melts up to 400 pounds each have been made in this apparatus. The total time required was usually about one hour for each 100 pounds of batch. Energy consumption was never very accurately determined, but varied from one-half to three-fourths of a kilowatt-hour per pound of melt.
The Evaluation of Barium Dioxide’ By E. C. Wagner U N I V E R S I T Y OF PENNSYLVAXI.4,
PHILADPLPHIA, P A .
HE eyaluation of barium dioxide depends upon decomposition by an acid and determination of the hydrogen dioxide produced. The latter is commonly accomplished by titration with permanganate, or the decomposition by acid may be effected in presence of pota,.:’ wum iodide and the liberated iodine titrat’ed with iodine. This paper deals only with these two methods from among the limited number that have been d e v e l ~ p e d . ~ A decision as to the actual accuracy of any method is difficult, for so far as the writer knows there is no way to determine the barium dioxide content of a sample with certainty. For present purposes it seems permissible, because of the comparative instability of hydrogen dioxide solutions in presence of traces of common impurities, finely divided solids such as dust, or even rough glass surfaces, and the consequent tendency toward low results, to assume the superiority of that method which yields the highest consistent resuits when precautions are taken to prevent positive error.
hydrochloric acid by the dioxide or by the permanganate, that the use of >In-- was without advantage, and that solutions of hydrogen dioxide obtained from barium dioxide could be allowed to stand for 15 minutes without apparent decomposition. Chemists who have assayed barium dioxide will probably question the last finding, as it must be connnon experience that the permanganate method is very likely to give low and irregular results, especially in warm weather. It mas found by R. E. Beard that the procedure given by Treadwell and Hall yielded concordant results only when decomposition and titration were conducted a t 5’ to 10’ C.; a t higher temperatures, including all ordinary laboratory temperatures, results were low and less regular. The directions of Treadwell-Hall are satisfactory only when the words “cold water” are interpreted to mean water very nearly a t the freezing point. The 2 iV hydrochloric acid used should be similarly chilled, and in hot weather it is advisable to cool the beaker externally during the analysis. In order to eliminate these inconveniences a means v a s Permanganate Method sought by which the hydrogen dioxide solution could be A typical form of this familiar method is described by stabilized long enough to permit titration a t ordinary temperatures. Acids in general are said to have a preservative Treadwell and H a L 3 The method was proposed by who found that’ hydrochloric acid was preferable to sulfuric action, and it is well known that phosphoric acid is very for decomposition, that with a 0.5 N concentration of hydro- effective. The possible usefulness of this acid came to the chloric acid there was no irregularity due t o oxidation of writer’s attention as a suggestion from E. H. Korton, with whom some trials were carried out jointly in 1918. I t was 1 Received February 14, 1925. found later that the use of phosphoric acid, and also of ice2 Kassner, A r c h . Phatm., 228, 432 (1890); Quincke, Z . anal. Chem., cold water, are described by Schimpf.6 The convenience S1,23 (1892); Raumann, Z . angew. Chem., 6, 116 (1892); Rupp, A r c h . Phorm., and also probably the accuracy of Schimpf’s procedure are 240, 437 (1902); also see Merck, “Chemical Reagents,” 2nd ed., 1914, p . 52; Lob, Chem. Ztg., SO, 1275 (1906); Chwala, Z . angew, Chens., 21, 589 (1906). diminished by the operation of diluting the solution of hy-
T
8 4
“Analytical Chemistry,” Vol. 11, 6th ed., 1924, p. 534. Lac. cit.
0
“Manual of Volumetric Analysis,” 5th ed., 1909, p. 161.
INDUSTRIAL A N D ENGl‘NEERING CHEMISTRY
September, 1925
drogen dioxide and titrating an aliquot portion. Preliminary trials showed that the use of phosphoric acid alone, or of hydrochloric acid and sodium phosphate, or of hydrochloricphosphoric acid mixtures, permits successful analyses a t temperatures as high as 40” C. or above. Later work has fully confirmed these results, as will appear below. Barium dioxide before analysis should be ground in a mortar to reduce any lumps, and if the humidity is high it is well to keep the material in a desiccator. Hydration of barium dioxide seems to occur readily in moist air, and this must be considered especially when the sample is treated with water, as the lumps or cakes of hydrate hare been observed to dissolve rather slowly in acid, and their presence to be associated with low results. To avoid error from this cause, samples were transferred to dry beakers, were analyzed promptly, and the water was added suddenly, so as to dihintegrate the hydrated sample as thoroughly as possible. The first drops of permanganate are sometimes not promptly decolorized, an annoyance prevented by addition of a trace of 1In-T as manganous chloride.
973
The identity of the results by all three methods a t lower temperatures, the unfavorable effect of increasing temperature upon the method using hydrochloric acid alone, and the marked effectiveness of phosphoric acid in stabilizing the hydrogen dioxide solution, are all shown by these results, and more clearly by the figure. For general use the hydrochloric-phosphoric acid method is recommended, as samples dissolve more readily in this liquid than in diluted phosphoric acid alone and the end point is a little more definite. The analyses shown indicate the lot of barium dioxide to be very nearly 88.25 per cent pure. The manufacturer‘s label gave the purity as 86.6 per cent, a value lower by 1.65 per cent. A second lot of “C. P. Analyzed” barium dioxide assayed 87.15 per cent, and was labeled to be of 86.2 per cent purity, a d u e 0.95 per cent lower. Both lots, it will be noted, mere better than was claimed by the manufacturer; it can scarcely be doubted that this was the result of faulty analytic method in the control laboratory rather than of charitable design.
Procedure
A sample of 0.25 to 0.3 gram was weighed out rapidly in a scoop and transferred to a 400-ml. beaker dried a t 100” C. S o t more than two or three samples were ii-eighed at one qitting, for the reason suggested above. The sample vas churned up as thoroughly as possible by the sudden addition of 50 nil. of water a t the desired temperature, and 200 nil. of one of the titrating solutions (see below), also a t the selected temperature, were added. Titration with 0.1 S permanganate was begun coincidentally with the addition of the acid solution, and was continued rapidly and with stirring until the end point mas approached. The titration n-as carried to a pink tint which showed a reasonable degree of persistence-i. e., which did not fade very perceptibly while the next analysis, or a blank, was titrated to the same color. -1 blank was run for each group of not more thaii four analyses, all conditions of the analyses being duplicated in the blank. The blank titrations varied usually from 0.03 to 0.10 nil. of 0.1 Spermanganate, corresponding to 0.11 to 0.36 per cent of liarium dioxide, and therefore not to be ignored. Titrating Solutions
MI /liter 50
Concentrated HCI 1 0 % M n C h 6H?O Concentrated HCI 85% Phosphoric acid 1 0 ~ i i l a n g a n o u chloride s 8 5 7 , Phosphoric acid 10% Mansanous chloride
Solution G Solution H Solution I
1
25 10 1
50 1
Analytical Results Temperaturea
Solution G (HCI)
0 t o 10
S8.28
c.
PER CEXT RAOI-Solution If (HCI HAPOI)
+
as. 18
b8.21 88.PO
85.35 88.14 88.20 (88.04) c 88.26
s8.m
85.35
S7.93 Xi.89 Si.89
88.14 88.23
S8.14
Av. 1 7 t o 21
Av.
2s t o 30
S6.83 87.36 s i , 52
.%v.
88.25 88.26 88.32 88.18
87.91 ’
87,?4
88.25 85.07 88.11 58.11 Av.
88.10
Solution I (HsPO2) S8.29
ss.25 ,
(88 5 0 ) h
88.27 8 8 , 29
88.25 ( S i . 93)’) 88.17
88.2.5
ss.23 88.P j
S i .si Si,S i S i . 72 87.83 Si.82 S i . 93
Av. 87,88 a variations of several degrees beyond these limits occurred in individunl experiments, b Results in parenthe5es discarded, c Sample liad caked on standing.
i
10
- _--__--HsPo4
20
30
40
50’C
----
H CI -HCI+YPO,
Iodometric Method
Proced lire 6 .Ibout 0.25 gram of barium dioxide n-as transferred to a 250-ml. Erlenmeyer flask, previously dried at 100” C. The
