The acid turns logwood violet to a fine red, and equally reddens orchil violet. But the two colors cannot be confounded, first, because the two violet shades are very distinct, that of orchil being much the brighter; and secondly, because ammonia has no action on logwood violet, while it turns orchil violet, if at all reddish, to a blue shade. Hydrochloric acid, whether dilute or concentrated, is without action on alkanet violet. If the acid is dilute, it is equally without action on Perkin's violet and dahlia. If it is strong, it turns them blue, and even green if in excess. Hofmann's violet turns green even with dilute acid, but prolonged washing restores the original violet shade. Dahlia gives a more blue shade than Perkin's mauve. The action of acid is equally characteristic for methyl violet. It becomes green, then yellow. Washing in water re-converts it first to a green, and then to a violet. The second group includes madder violet, cochineal violet, and the compound violet of cochineal and extract of indigo. These three dyes are thus distinguished: Hydrochloric acid turns the madder violet-orange, slightly brownish, or a light brown, and it affords the characteristic reaction of the madder colors described above under reds. Cochineal violets are reddened. Sometimes they are decolorized, and become finally yellow, but do not pass through a brown stage. The compound violet of cochineal and extract of indigo presents this characteristic reaction, that if boiled with very weak solution of sodium carbonate the liquid becomes blue, rather greenish, while the cloth becomes a vinous-red--_Moniteur Scientifique.--Chem. News._ * * * * * CHEVALET'S CONDENSO-PURIFIER FOR GAS. The condenso-purifier shown in the accompanying cut operates as follows: Water is caused to flow over a metallic plate perforated with innumerable holes of from one to three millimeters in diameter, and then, under this disk, which is exactly horizontal, a current of gas is introduced. Under these circumstances the liquid does not traverse the holes in the plate, but is supported by the gas coming in an opposite direction. Provided that the gas has sufficient pressure, it bubbles up through the water and becomes so much the more divided in proportion as the holes are smaller and more numerous. The gas is washed by traversing the liquid, and freed from the tar and coal-dust carried along with it; while, at the same time, the ammonia that it contains dissolves in the water, and this, too, so much the better the colder the latter is. This apparatus, then, permits of obtaining two results: a mechanical one, consisting in the stoppage of the solid matters, and a chemical one, consisting in the stoppage of the soluble portions, such as ammonia, sulphureted hydrogen, and carbonic acid. [Illustration: FIG. 1.--CONDENSO-PURIFIER FOR GAS. (Elevation.)]