February, 1923
INDUXTRIAL AND ENGINEERING CHEJUXTRY
kelpchar industry, consideration would have to be given the iodine (contained in the brine with the potash), which alone is able to bear the costs here entered against the potash and still leave a profit on the iodine. Thus, by carrying the method of computing costs a step further, all manufacturing costs charged against potash may be made to disappear. The great initial purity of kelp brines and the ease with which all impurities are removed from the potash salts re-
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sulting from their evaporation make kelp a peculiarly favorable raw material for the manufacture of a chemical grade of potassium chloride. Only slight modifications in the process adopted for the manufacture of potash of fertilizer grade render it of a purity which will satisfy the most exacting demands. The cheapest source of American potash for fertilizer purposes, it may as easily become an equally cheap source of a chemical grade of potash.
Rapid Determination of Potash in Acid-Insoluble Silicates By Manuel M. Green MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASS,
HE DETERMINATION of potash in an acid-insoluble silicate by decomposition of the sample with sulfuric and hydrofluoric acids, and precipitation of the potassium as cobaltinitrite after a basic acetate separation2 requires about as much time as the regular J. Lawrence Smith method, and leaves much to be desired. It is, of course, true that, by following a definite procedure using definite amounts of reagents and making certain corrections, there may be developed some methods which are accurate within certain limits. But in cases where potash is not being determined continually, such means are not satisfactory, and this method has therefore been developed. BASISOF THE METHOD The strong dehydrating power of concentrated perchloric acid is well known, as is alsp the fact that the alkaline earth perchlorates are soluble in alcohol. Furthermore, according t o the cobaltinitrite method3 if the potash is determined as perchlorate, the cobalt is not removed but is dissolved out as perchlorate by the alcohol. This latter fact suggested the possibility of all metals except potassium forming alcoholsoluble perchlorates, and this assumption was made in working out the method. METHOD As finally worked out, the method is as follows:
T
Weigh out into a platinum crucible 0.15 to 0.35 g. of the sample, add 1.5 cc. of 2 N perchloric acid, then 3 to 4 cc. of 48 per cent hydrofluoric acid, and evaporate to fumes of perchloric acid. Cool, add water t o fill crucible two-thirds full, heat to boiling, filter, and wash thoroughly with hot water, catching filtrate and washings in a platinum dish. Evaporate to perchloric acid fumes, cool, add 25 cc. of 97 per cent alcohol. Break up residue with a stirring rod, filter on an untared Gooch (which has previously been washed with a one per cent solution of perchloric acid in 97 per cent alcohol), and wash thoroughly with perchloric acid-alcohol wash water. (It is necessary that the residue be broken up as much as possible, and that the residue be fine and crystalline before filtering, as otherwise the following procedure will have to be repeated.) Transfer the asbestos mat by means of a stirring rod to a filter and wash the crucible with hot water, allowing the washings to fall on the filter containing the mat. Wash the mat and filter thoroughly with hot water, catching the filtrate in a platinum dish. (By this washing most of the iron and aluminium salts seem to be decomposed, leaving them as insoluble basic salts on the filter paper. Omission of this washing and subsequent evaporation gives results several per cent too high.) Add 0.5 to 1.0 cc. of 2 N perchloric acid, evaporate to fumes, cool, add 25 cc. of 97 per cent alcohol, break up
* Received August 28, 1922. * Hillebrand, “Analysis of Silicate and Carbonate Rocks,” U. S. Geol. Survey, Bull. 700, 210. * I b i d . , 216.
the residue with a stirring rod, and filter the potassium perchlorate on a tared Gooch, which has previously been moistened with perchloric acid-alcohol wash water, wash with perchloric acidalcohol wash water, and dry a t 110” C. to constant weight. Weigh as potassium perchlorate. Time, 2 to 3 hrs. (If previous to this evaporation the product was not quite crystalline, the potassium perchlorate should be redissolved and the evaporation with perchloric acid repeated. If precipitate is pure potassium perchlorate, the weight then obtained will check with previous weight by j=0.0003 g.) To correct for sulfate, the precipitate should be redissolved in hot water as described above and a drop of barium chloride solution added. If sufficient precipitate is obtained, it should be filtered off and the evaporation with perchloric acid repeated. Generally, however, this correction is unnecessary.
Using this procedure, eight samples of silicates were analyzed .(in triplicate) with the following results. G. Sample No. Taken
1 2 3
4
6
7 8
0.3075 0.3027 0.1221 0.1499 0.2596 0.2745 0.1614 0.1617 0 1605 0.1709 0.1707 0.2745 0.1601 0 1457 0.2360 0.2359 0.2006 0.1576 0.1573 0.1886 0.1863 0.2284 0.3589 0.1941
G. KClOa Obtained
Per cent Kz0 Found
0.1003 0.0986 0.0402 0.0547 0.0638 0.1007 0.0298 0.0308 0.0294 0,0625 0.0613 0.1007 0.0594 0.0535 0 0890 0.0872 0.0755 0.0589 0.0465 0.0548 0.0538 0,0124 0.0192 0.0104
11.09 11.08 11.17 12 40 12.28 12.47 6 28 6.48 6 23 12.44 12.21 12.47 12.61 12.48 12.81 12.56 12.79 12.70 10.02 9.88 9.83 1.85 1.82 1 82
Per cent1 KzO by Average J. I,. Smith of Detns. Method 11.11
11.26
12.38
12.32
6.33
6.43
12.37
12.32
12.63
12.65
12.68
12.78
9.91
9.892
1.83
1.892
Values obtained by U. S. Geological Survey. Value obtained by U. S. Geological Survey for No. 7 was 8.99 per cent, for No. 8 was 0.90 per cent, but check analysis by the author (J. I,. Smith method) gave values indicated. 1 2
CONCLUSION While it would be necessary to investigate this method more carefully if it were desired to use it for work requiring accuracy to more than * 0.2 per cent, the method as given is as accurate as is desired for commercial work, and removes the determination of potassium in silicates from the list of analyses requiring a long and tiresome procedure for their completion. ACKNOWLEDGMENT The author wishes to thank Dr. Steign, chief chemist of the U. S. Geological Survey, for his kindness in supplying the samples analyzed by the J. Lawrence Smith method in his laboratories, which were used in this investigation.
