Vol.. 8, No. 9
ANION GROUP TESTS
1801
An unusual opportunity for the discussion of solubility product, common ion, complex ions, and the ionization of polybasic acids in stages is given in the study of the groups of anions which precipitate with silver nitrate in acid solution, which precipitate in ammonia solution, which precipitate in acid but not in ammonia solution, and which precipitate in neutral but not in either acid or ammoniacal solution. The adjustment of the conditions in the solution, so as to test for each of these groups of silver salts, the writing of the equations for the reactions involved, and the explanation of the observed phenomena, in the light of the words a t the beginning of the paragraph, all serve to impress important chemical principles on the mind of the student. Last, but not least, the anion group tests help the student get acquainted with the anions and their reactions. Almost every one of the metals forming the cations studied in elementary qualitative analysis is familiar to the student, either as a free element, or in some compound associated with his every-day life. The same is not true of the anions. Such words as ferrocyanide, ferricyanide, thiosulfate, and tartrate usually mean very little to the qualitative student when he starts his anion procedures. The lack of system in these procedures usually adds to his bewilderment. Likely the carrying out of any reactions of the anions would serve to introduce the student to these more or less unfamiliar radicals, but it is our opinion that this can be done more easily with a few group reactions than with a much larger number of individual reactions. After the student becomes acquainted with the anions, and some of their group reactions, it becomes easier for him to learn specific tests for each anion, particularly if these tests are based on some anion group tests, as many are. Literature Cited
A New Industrial Chemical, Anhydrous Hydrofluoric Acid. Commercial hydrofluoric acid has in the past always contained from i l l to 411% water, and is best known as one of the few chemicals that will attack glass, so that it cannot be kept in glass bottles. Recently the first tank car of anhydrous bydrofluoric acid was shipped by the producers of this new industrial chemical, Sterling Products Company of Easton, Pennsylvania. T h e anhydrous acid, which is made from fluorspar and sulfuric acid, boils a t ISDC.,has a specific gravity approximately the same as that of water, and can be shipped in steel containers; it has a great affinity for water, will char a piece of wood, and is very destructive to rubber. At present it finds its chief use in the manufacture of ~lifluorodichloromrthane, the new refrigerant, the advent of which we mentioned i u uur issue of May, I R J f l . Availability of the anhydrous acid will probably lead to its rrnphyment in connection with other processes.--lnd. Ball., Arthrrr I). Lilllr, l a r .
