All these salts detonate much more powerfully when heated in close vessels, than when heated in the air; and it was a curious thing to observe, that those with bases yielding oxygen most readily, were those which exploded with least force. By heating some of the salts previously mixed with chloride of potassium, &c., to retard the action, it appeared that no carbonic oxide, but only carbonic [p214] acid and azote were evolved during their decomposition by heat.
_On the Bitter Principle from Aloes_.—Upon distilling 8 parts of nitric acid from 1 part of the extract of aloes, and adding water to the remaining fluid, a resinous reddish yellow substance precipitated, which, by washing, became pulverulent—it was discovered by M. Braconnot. Upon evaporating the liquid separated from the precipitate, it gave large yellow rhomboidal crystals, not transparent, and but slightly soluble. These crystals, at first mistaken for a particular substance, were soon found to be a combination of oxalic acid with the bitter of aloes. The bitter substances of aloes dissolved in 800 parts of water, at 59° F., but in a smaller quantity of boiling water. This solution has a superb purple colour. Silk boiled in it acquired a very fine purple colour, on which neither soap nor acids effected any change, except nitric acid; this changed the colour to yellow, but it was restored simply by washing in water. All shades may be given to this colour by proper mordants. Wool is dyed black in a peculiarly beautiful manner, by the same process, and light has no influence on the colour. Leather acquires a purple colour; cotton, a rose colour; but the latter will not resist soap. Dr. Liebeg thinks that this is the only substance from which a permanent rose dye for silk may be expected.—_Ann. de Chimie_, xxxv. 72.
25. _On the Existence of Crystals of Oxalate of Lime in Plants_.—M. Raspail has read a memoir to the Academy of Sciences, to prove the analogy which exists in arrangement between the crystals of silica, which are found in sponges, and those of oxalate of lime occurring in the tissue of phanerogamous plants.
The latter crystals were observed, for the first time, by Rafn and Jurine, who regarded them as organs of which they knew not the use. They were then observed by M. de Candolle, who called them _raphides_, and gave a figure of them, which, however, is inaccurate. These crystals are really very regular tetraedrons. In many plants, as _orchis_, _pandanus_, _ornithogalum_, _jacinthus_, _phytolaca_ _decandria_, _mesembryanthemum deltoides_, &c. they are very small, not being more than 1/200 of a millimetre (.0002 of an inch) in width, and 1/10 (.004 of an inch) in length. But, in the tubercles of the Florence iris, they are as much as 1/50 (.0008 of an inch) in width, and 1/3 (.01312 of an inch) in length, so as to be easily capable of examination.—_Bull. Univ._ B. xi. 376.