Organic chemistry / by W.H. Perkin and F. Stanley Kipping.

  • Perkin, W. H. (William Henry), 1860-1929
Date:
1905
Catalogue details

Licence: In copyright

Credit: Organic chemistry / by W.H. Perkin and F. Stanley Kipping. Source: Wellcome Collection.

    42/660 (page 22)
    C 62-40 per cent. H 4-31 0 33-29 ii (by difference). The percentage of oxygen is always obtained by difference, there being no satisfactory method by which this element may be directly estimated. The following points remain to be noticed in connection with the determination of carbon and hydrogen. If the substance contain nitrogen, it is necessary to insert a roll of bright copper gauze, about four inches long, into the front part (b) of the tube in the place of some of the copper oxide; this is kept red hot during the combustion, and serves to decompose any oxides of nitrogen* produced during the operation, which would otherwise be absorbed by the water in the calcium chloride tube and by the potash, and thus lead to erroneous results. When the sub- stance contains a halogen, a roll of silver gauze must be used in order to prevent any halogen or halogen compound of copper from passing into the absorption apparatus ; usually, in analysing a substance containing halogens, sulphur, or phosphorus, the space / to / (fig. 8) is filled with lumps of fused lead chromate instead of copper oxide. Lead chromate, like copper oxide, is a powerful oxidising agent at high temperatures, its action being probably represented by the equation, 4PbCr04 = 4Pb + 2Cr203 + 10 0. Any sulphur dioxide, phosphorus pentoxide, or halogen pro- duced during the combustion is completely retained by the lead, as PbS04, PbCl2, &c., and thus its passage into the absorption apparatus is prevented. * In order to render the roll of gauze as efficient as possible, it is heated in a blowpipe flame until thoroughly oxidised, and, while red hot, dropped into a little (1 c.c.) pure methyl alcohol contained in a test tube ; the methyl alcohol reduces the copper oxide, giving a very bright surface of copper. The roll is then completely freed from methyl alcohol by heating at 160-180° for half-an-hour, just before commencing the combustion.