In performing an analysis a little freshly prepared oxide of copper is first introduced into the combustion tube, then a mixture of about 5 grains of the substance to be analyzed, with an excess of the oxide, while the tube is lastly filled to within an inch of its open mouth with the oxide alone. The tube is then placed in the furnace, winch may be heated with charcoal or gas. (lIofman's gas furnace, in which is a peculiar form of burner called the atmopyre, is the best. It is described in vol. xi. of The Journal of the Chernired Swirty,) Red-hot charcoal is now placed round the anterior part of the tube, containing the pure oxide of copper; and when this is red-hot, the fire is slowly extended towards the further extremity by shifting the movable screen shown in the figure. When the tube has been completely heated from end to end, and no more gas is disen gaged, the charcoal is gradually removed from the further extremity of the tube, and the point of the latter broken off; after which a little air is drawn through the whole appar atus, so as to secure any remaining carbonic acid and watery vapor. The parts are then
detached, and the increase of weight of the chloride-of-calcium tube and potash appar. atus is determined by an accurate balance. The following account of an actual analysis of crystallized cane-sugar (borrowed from Fownes's Chemistry) will serve to illustrate the preceding remarks: Grains.
Quantity of sugar employed 4.750 Potash apparatus, after experiment. 781 13 before experiment 773.82 Carbonic acid 7.31 Chloride-of-calcium tube, after experiment 226.05 before experiment.... 223.30 Water 2.75 grains carbonic acid =1.994 grains carbon, and 2.75 grains water = 0.3056 grains hydrogen: or iu 100 parts of sugar, carbon, 41.98; hydrogen, 6.43; oxygen by difference, .51.59.
For the methods of determining other elements quantitatively, such as nitrogen, chlorine, sulphur, phosphorus, etc., we must refer to the various works that have been published on organic analysis, amongst which those of Liebig, Fresenius, and Rose deserve special mention.