A given quantity of this indigogene was acted upon by ammonia, and the weight of the undissolved blue portion ascertained, it appeared that the weight of the pure portion dissolved was 0.404 grammes (6.224 grains.) The solution was put into an inverted [p221] jar, over mercury, and oxygen gas gradually passed in until absorption ceased, and then the liquid containing the precipitated indigo was evaporated to dryness at 212°. The weight of the substance was increased to 0.047, i. e. 11.5 per cent.
Not having obtained indigogene perfectly pure, M. Liebeg did not attempt to analyze it for the ultimate composition. He remarks, that indigo is, perhaps, the only organic body from which one of its constituent parts may be taken without total decomposition; and which, by oxidation, passes to the state of an indifferent body, having much analogy with peroxides.—Ann. de Chimie, xxxv. 269.
39. On the mutual Action of Ethers, and other Substances.
Nitric and acetic ethers are described as being easily decomposed by the action of many bodies without the assistance of heat, if aided by time. Amongst the products of the action are the acids of the ethers, acetates, and alcohol which dissolves the salts formed.—Jour. de Chimie Méd.
40. Faraday’s Chemical Manipulation.
The mistake, which arose from using the wrong specific gravity of two that were required in calculation, occurs in the paragraphs (599, 600,) but fortunately is prevented from occasioning any experimental error by the directions given in (602). The acid of specific gravity, 1.141, directed to be used, is too strong for the quantities marked upon the tube. The substitution of one of specific gravity 1.127, will correct the error, and may be obtained very nearly by mixing 19 parts, by weight, of strong oil of vitriol, with 81 parts of water.
The alterations required may be made in the volume with a pen, as for errors of the press, by reading “1.127” for “1.141” in lines 25 and 30 of page 276, and lines 2 and 13 of page 277; and “nineteen” for “one” in line 27, and “eighty-one” for “four” in line 28 of page 276.—M. F. [p222]
III. NATURAL HISTORY. [◊]
1. On the Supposed Influence of the Moon, by M. Arago.
M. Arago explains this observation of practical men, by a reference to the facts and principles established by Dr. Wells. He has shown that, in a clear night, exposed bodies may frequently have their temperatures reduced below that of the surrounding atmosphere, solely by the effect of radiation, the difference being as much as 6, 7, 10, or more degrees, but that it does not take place when the heavens are obscured. M. Arago then observes, that the temperature is often not more than 4, 5, or 6 degrees above the freezing point during the nights of April and May, and that when the night is clear, consequently when the moon is bright, the temperature of the leaves and buds may often be brought by radiation below the freezing point, whilst the air remains above it, and consequently an effect be produced, which, though not dependent upon, accompanies the brilliant unobscured state of the moon—the absence of these injurious effects, when the moon is obscured, being also as perfectly accounted for by these principles, from the knowledge that the same clouds which obscure the moon will prevent the radiation of heat from the plants. Hence, as M. Arago observes, the observation of the gardener is correct as far as it goes, though the interpretation of the effect which he generally gives is incorrect.—Annuaire du Bureau des Long. 1827, p. 162.