laboratories is not perfectly pure, but that it contains substances that will change in time. These substances might be mineral or organic, or even living organisms. Wishing to ascertain whether the last was the case, I added to the water in one of the tubes 10000 of bichloride of mercury, while I left that in the other tube unchanged. The small quantity of bichloride did not at all affect the color of the water to which it was added. In the course of six days the water which had been left alone became blue-green, while that to which bichloride of mercury had been added preserved a fixed blue, and exhibited no sign of change for three weeks; but, when the salt was put into the water that had turned blue-green, that began slowly to turn blue again, and this process continued for nine days, when it stopped, without the blue color having been quite restored. Inasmuch as the bichloride of mercury is extremely deadly to minute organisms, we have a right to conclude that life exists in the distilled water of laboratories, and that such water contains also the aliments required for its development. How can organic germs exist in water that has just passed through the process of distillation? Tyndall has shown the possibility of vapor taking up germs as it passes through the air. M. Stas has proved that distilled water may contain volatile organic matters which after a little while become spontaneously fixed. We may, then, conclude that our distilled water continued blue as long as the organic matters contained in it continued volatile, but that it turned green as they became fixed.
It was necessary to obtain distilled water certainly free from organic matter. I did this by an adaptation of M. Stas's process of distilling spring-water over a mixture of manganate and permanganate of potash into a cooling-vessel of platinum. The resultant water, which met every test of its purity, when placed in the tubes, displayed a color to which only the clearest blue of the sky, as seen from a mountain-top on a perfect day, can be compared, the hue of which was not changed after it had been left in the tubes for two weeks. The color was evidently not due to reflection from minute particles, for it was a color of transmission and had not a tinge of red in it; moreover, if it was due to the presence of foreign particles, all liquids under the same conditions ought to have a bluish tinge. But amylic alcohol, distilled under circumstances favorable to the absorption of fine particles, was colorless, while acetic acid and ethylic alcohol were yellow, when seen through a thickness of five metres; and, though the color was effaced as the thickness of the masses was reduced, no trace of green or blue appeared in the liquids. It seemed proved to me that water, as pure as we can get it, has a blue color, which proceeds, not from reflection, but from an absorption of the yellow.
To perfectly clear lime-water I added enough of a solution of carbonic anhydride to cause the formation of a barely visible precipitate, and then poured the liquid into one of my tubes of observation. The