Analytical reagents : standards and tests / compiled by Edmund White.

Date:
1911
Catalogue details

Licence: In copyright

Credit: Analytical reagents : standards and tests / compiled by Edmund White. Source: Wellcome Collection.

    24/194 (page 12)
    platinum crucible should leave a white saline residue. On heating this with the flame it should volatilise, leaving less than 0 5 Mg. residue, and the substance should remain colour- less during volatilisation. Sulphate: A 10 -per cent, solution should show no turbidity after addition of 1 mil barium chloride solution and standing two hours. Metals: A 10 per cent, solution should show no darken- ing on the addition of an equal volume of hydrogen sulphide solution. Iron: A 5 per cent, solution should not show any im- mediate blue colour on the addition of one drop of potassium ferrocyanide solution. Even the best obtainable samples will seldom stand a more stringent test than this. Thiocyanates: The addition of a few drops of ferric chloride solution to a 5 per cent, solution acidulated with hydrochloric acid should not produce an immediate red oolour. Organic Impurities: A 5 per cent, solution rendered pink by the addition of N/10 potassium permanganate solution should be only slowly decolorised and should not become brown. Trade Varieties. This salt is met with in many forms. Sal ammoniac is the name applied to the sublimed substance in crystalline lumps, showing a columnar stratification on fracture. When crushed to small pieces it is U6ed for charging Leclanche batteries. A commercial form of granular crystals is also sold, as well as another form of crushed crystals made to resemble crushed sal ammoniac, and known as dog-tooth crystals. These varieties usually oontain more cr less of the impurities mentioned above and always considerable traces of iron and fixed impurities. The less pure samples have a reddish or greyish tint. AMMONIUM FLUORIDE. nh4f. Colourless translucent crystals, very soluble in water. The aqueous solution has an acid reaction owing to the easy dissociability of the salt. It attacks glass, and should be stored in vessels of gutta percha or paraffin wax. Glass bottles may be used if first thickly coated internally with paraffin wax and closed with a stopper of the same material. Tests. Residue: 5 grammes ignited in a platinum dish should leave not more than 0'2 Mg. residue. Chlorides: The addition of silver nitrate and nitric acid to a 5 per cent, solution should give no turbidity. Sulphate and Silicofluoride A 5 per cent, solution