(v.) Fragment of a used crucible from the glass works of Bagneaux, near Nemours; it had been made from the clay of Forges (Seine Inférieure).
(vi.) A used crucible from a Bohemian glass-house.
(vii.) Bricks with which the blast furnaces at Creusot are [p480] constructed; they are made of a mixture of baked and unbaked clay.—Annales de Chimie, i. 469.
28. On the Composition of simple Alimentary Substances, by Dr. Prout.
Dr. Prout’s first object was to devise, if possible, an unexceptionable mode of determining the proportions of the three or four principles, which, with few exceptions, form organic bodies; and after numerous trials, he adopted a method founded upon the following well known principles. When an organic product, containing three elements, hydrogen, carbon, and oxygen, is burnt in oxygen gas, one of three things must happen: i. The original bulk of oxygen gas may remain the same, in which case the hydrogen and oxygen in the substance must exist in it in the same proportions in which they exist in water; or, ii. The original bulk of the oxygen may be increased, in which case the oxygen must exist in the substance in a greater proportion than it exists in water; or, iii. The original bulk of the oxygen gas may be diminished; in which case the hydrogen must predominate. Hence it is obvious, that, in the first of these cases, the composition of a substance may be determined, by simply ascertaining the quantity of carbonic acid gas yielded by a known quantity of it; while, in the other two, the same can be readily ascertained by means of the same data, and by noting the excess or diminution of the original bulk of the oxygen gas employed.
The apparatus consists of two inverted glass syphons which act the part of gasometers; these are connected when required, by a small green glass tube, in which the substance is to be decomposed and burnt: the syphons are very carefully gradated; so that the quantity of gas in them can be accurately estimated; and are supplied with cocks both above and below, so that they can be filled with mercury, the mercury drawn off and gas introduced, the gas transferred through the green glass tube, or the contents retained in an undisturbed state, with the utmost readiness and ease. The substance to be decomposed, may be put into a platina tray, and introduced alone into the green glass tube, and being there heated by a spirit lamp, be burnt in the gas passing over it; or it may be mixed with pure siliceous sand; or, what is most generally preferable, be mixed with peroxide of copper, which is always left, in consequence of the excess of oxygen gas used, in the state in which it was introduced. After the experiment the volume of gas is easily [p481] corrected for pressure, and if necessary for temperature, and the carbonic acid ascertained by the removal and analysis of a portion. No correction is required for moisture, the gas always being used saturated with water.
Dr. Prout considers the principal alimentary substances as reducible to three great classes, the saccharine, the oily, and the albuminous; and his paper relates to the first of these. This, with certain exceptions, includes the substances in which, according to MM. Gay Lussac and Thenard, the oxygen and hydrogen are in the same proportion as in water. Such substances are principally derived from the vegetable kingdom, and being at the same time alimentary, Dr. Prout uses the terms saccharine principle and vegetable aliment as synonymous.
The following tables show some of Dr. Prout’s results with several substances, extreme care having been taken in every case to obtain the bodies pure, and new processes often resorted to for that purpose.
| SUGAR. | ||
|---|---|---|
| Carbon. | Water. | |
| Pure sugar-candy | 42.85 | 57.15 |
| Impure sugar-candy | 41.5 to 42.5 | 58.5 to 57.5 |
| East India sugar-candy | 41.9 | 58.1 |
| English refined sugar | 41.5 to 42.5 | 58.5 to 57.5 |
| East India refined sugar | 42.2 | 57.8 |
| Maple sugar | 42.1 | 57.9 |
| Beet root sugar | 42.1 | 57.9 |
| East India moist sugar | 40.88 | 59.12 |
| Sugar of diabetic urine | 36. to 40? | 64. to 60? |
| Sugar of Narbonne honey | 36.36 | 63.63 |
| Sugar from starch | 36.2 | 63.8 |
| AMYLACEOUSPRINCIPLE. | |||
|---|---|---|---|
| Carbon. | Water. | ||
| Fine wheat starch | 37.5 | 62.5 | |
| " | dried (i.) | 42.8 | 57.2 |
| " | highly dried (ii.) | 44 | 56 |
| Arrow root | 36.4 | 63.6 | |
| " | dried (iii.) | 42.8 | 57.2 |
| " | highly dried (iv.) | 44.4 | 55.6 |