land by Chapman and Hall in 1950, and my American edition was published by the Chemical Publishing Co. of New York in 1952.
T o the Editor: Perhaps other teachers of chemistry have, like me, To the Editor: had scant certainty of mhat becomes of the cryolite The recent article by D. D. DeFord (THISJOURNAL, so essential in the reduction of aluminum from its 31, 460 (1954)) mentions that solubility products are ore. Textbooks generally seem to consider it of little frequently not accurately known, and that mauy calcu- importance. Statements about it often leave the lations in quantitative analysis may therefore be of little implication that since "theoretically it lasts forever" value. no further attention to its performance is in order. I think it may be interesting to mention one notable Schlesinger,' in a footnote, says the "quantity [of example, inasmuch as it affects the validity of that cryolite] used up is relatively small." He further classic calculation, the determination of the exact states that there is now an artificial cryolite availchromate ion concentration necessary to make the end- able to supplement the limited natural mineral supply point in Mohr's method coincide with the equivalence obtainable only from Greenland. point. This calculation requires the use of the soluhilThe facts appear to be that not only does the cryity products of both silver chloride and silver chromate, olite not "last forever" but that the quantity needed quantities which one would imagine to he known to a by huge modern reduction plants is by no means small. high degree of accuracy. For every ton of free metal produced, it is reliably In five leading texts of quantitative analysis puh- stated2 that one-tenth of a ton of cryolite is lost. One lished between 1943 and 1954 one finds that the solu- of the Reynolds plants3 is currently producing 100 bility products of silver chromate cover the range from million pounds of aluminum metal per year. Obviously 0.57 t o 9.0 X and even the solubility product of 10 million pounds of cryolite is not a small quantity. silver chloride ranges from 1.0 t o 1.7 X 10-10. The ex- Its loss is something to be reduced. treme range of "correct" chromate ion concentrations Another aspect of cryolite's place in the company's using these values would be 0.003 to 0.09 molar. concern is its part in the adverse publicity of litigations In each of the texts the calculation is made, and then that involve thousands of dollars. One such suit the observation that this is not the "practical" chromate for damages alleged to have been entailed by a dairy ion concentration t o use, only the theoretical. How- herd was recently reduced by the court from $42,000 ever, even the practical values suggested ranged from to $14,000 "in view of the corrective measures which 0.002 to 0.01 molar, which hardly indicates perfect have been taken" by the defendant. Of the last unanimity. half of the period covered by the suit the judge said, "The defendant had installed fume controls which have proven effective." Here, as in many other industrial controls of wastes, the "corrective processing" has both reduced annoying litigation and at the same time salvaged a necessary To the Editor: processing chemical. By the combination of these With reference to the paper "The use of a radio-fre- captured gases and the scmbhiugs of reclaimed cryquency oscillator in student analysis," by James L. olite from the spent reduction cells, replacement for the 10 lnillion pounds of lost cryolite is produced Hall and his associates which appeared in THIS JOURNAL, 31, 54-9 (1954), as the originator of radio-frequency locally, an accomplishment, certainly, for economy, chemical analysis in 1936 and the first to apply r.-f. for and one that is of much interest to the public as well. I submit the above as of interest to chemistry that purpose by the application of external electrodes in 1944, I should like to congratulate the authors on their teachers. I t might also merit a "footnote" rating for paper. I am, however, disappointed not to have re- the students of the coulse. ceived credit in their reference list for my own work B. CLIFFORDHENDRICKS which opened the door to this new analytical field. WASHINGTON LONGVIEW, My work is described in detail with the dates and 1 "General Chemistry," Longmans, Green & Ca., New York, titles of my own and other workers' publications up to 1937, p. 179. the time of printing. My first edition, "Conductimetric l"Encyclopedia Britannica," 1951, Vol. I, p. 714. Analysis a t Radio-frequency," was published in EngIn Longview, Washington.
