Qualitative analysis / by William Briggs and R.W. Stewart.

  • William Briggs
Date:
1913
Catalogue details

Licence: Public Domain Mark

Credit: Qualitative analysis / by William Briggs and R.W. Stewart. Source: Wellcome Collection.

    136/180 (page 120)
    The barium chloride is next precipitated by ammonium carbonate: BaClo + (NH4)2C03 = BaC03 + 2 NH4C1, and the ammonium salt volatilized by heat. (d) The insolubility of potassium chloroplatinate, the corresponding sodium salt being soluble: 2 KOI + H2PtCl6 = K2PtCl6 + 2 HC1. Note.—If a brown coloration is produced when H2PtClg is added it proves the presence of an iodide in the solution e.cg. 2 Nal + H2PtCl6 = 2 Nad + 2 HC1 + PtCl2 + I2. In this case the solution should be boiled with a little UNO, to expel iodine. Addition of a further quantity of H2PtCl6 will now precipitate potassium if present. (e) In the decomposition of the excess of chloro- platinic acid, the starch* acts as a reducing agent and throws down metallic platinum, which is insoluble. Alternative method of removing magnesium. The use of baryta water for the separation of magnesium is, of course, necessitated by the fact that sodium phosphate is inadmis¬ sible, since sodium is to be tested for in the filtrate. If, however, ammonium phosphate, (NH4)2HP04, is available, this may be used to precipitate the magnesium, thug avoid¬ ing the baryta-water method, which is rather elaborate. In this case the following is the course of procedure:— Concentrate the filtrate from Croup V., add ammonia and ammonium phosphate in excess, and allow to stand in a warm place for some time. When a precipitate ceases to fall, filter and test the filtrate for Na and K. * Formaldehyde may preferably be used as reducing agent in place of starch. There is then no need to evaporate to dryness and ignite in order to bring about reduction, since chloroplatinic acid is reduced by formaldehyde on simply warming. The precipitate of platinum is filtered off and the filtrate tested for sodium as described.