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.

    68/180 (page 52)
    The separation from a dilute solution of a salt of mag nesium is promoted by heating gently and stirring with a glass rod. Very dilute solutions give a precipitate only after standing some hours in a warm place. 4. Heat strongly before the blowpipe on charcoal: moisten the residue with cobaltous nitrate, and again heat: a pale pink mass will be obtained. [.Distinction from zinc and aluminium.] Magnesium sulphate, MgS04, and magnesium chloride, MgCb, are the commonest soluble magnesium compounds. POTASSIUM, K. Solution—Potassium Chloride, KC1. 1. Place a few drops of the solution on a watch-glass, and add to it two or three drops of chloroplatinic acid, H2PtCl6,.and then a few drops of alcohol. If the solution is concentrated, a dense yelloiv crystalline precipitate of the chloroplatinate, K2PtCl6, is at once formed. 2 KC1 + H2PtCl6 = lUPtClg + 2 HC1. If the solution be dilute, the precipitate is obtained only after some time. Its formation can be hastened by rubbing the bottom of the watch-glass with a glass rod. The precipitate forms along the lines where the rod comes in contact with the watch-glass. In very dilute solutions no precipitate is obtained. Note.—Potassium iodide behaves abnormally. It gives a brown coloration owing to the liberation of iodine, but no precipitate, if only sufficient H3PtCl6 is present to oxidise the KI. (If more than this is present it will react with the KC1, produced as shown in the above equation, and a precipitate will be formed.) 2 KI + H2PtCl6 = 2 KOI + PtOlg + I2 + 2 HC1. The solution should be boiled for a few minutes with the