[Footnote: Continued from SUPPLEMENT No. 391, page 6240.]

To have these movements occur in a constant and invariable manner upon the surface of water, and especially upon mercury, it is necessary to take precautions in regard to cleanliness, this being something that we have purposely neglected to mention to our readers. For we wished, through this voluntary omission, to stimulate their sagacity by bringing them face to face with difficulties that they will perhaps have succeeded in overcoming, with causes of error that they will have perceived, and the principal one of which is the want of absolute cleanliness in the water, vessels, and instruments that they may have used for the experiments.

Thus, very probably, they will have more than once seen the camphor remain immovable when placed in vessels in which they had hoped to be able to see it undergo its gyratory and other motions. Their astonishment will have been no less than our own was when we noticed the sudden cessation of the camphor's motions under the influence of vitreous or metallic objects, such as glass rods or tubes, pieces of gold, silver, or copper coin, table knives, etc., dipped into the liquid in which such motions were taking place before the immersion of the objects under consideration.

The instantaneously sedative power of the human fingers, or of a hair, will have, perhaps, reminded them of some sort of sorcery, or of some diabolic art worthy of the great Albert.

APPARATUS FOR THE STUDY OF THE MOTIONS
OF CAMPHOR.

As for ourself, we confess that, after repeating the curious experiments of Mr. Dutrochet day after day, and scrupulously following his directions, we have, in the presence of our results, that were exactly identical with his, almost been tempted to believe ourself to be the victim of some occult power, or at least of some optical illusion, the true cause of which remained a mystery to us. Finally, after many fruitless attempts to find a key to the enigma that engaged our attention, the light finally dawned upon us, and then shone straight in our eyes.

In comparing the last results of our experiments with those that we had obtained previously, we saw, for example, that the camphor moved in the test glasses at a level that was notably higher than that at which its gyration took place the day before, or the day before that. And yet we had always used the same vessels, the same water, and particles detached from the same lump of camphor.

To what, then, could be due the difference observed between the two levels at which we had, in the first and last place, seen the camphor execute its movements? In the absence of any answer that was satisfactory, we finally suspected that the difference that we had noticed was ascribable to the fact that, after the numerous washings that the apparatus had been submitted to in having water poured into them to repeat the experiments, they had gradually been freed from impurities of whatever nature they might have been, and which, unbeknown to us, might have soiled their sides.

Starting with this idea, which was as yet a hyphothetical one, we began to wash our hands, glasses, etc., at first with very dilute sulphuric acid, and then with ammonia. Afterward we rinsed them with quantities of water and dried them carefully with white linen rags that had been used for no other purpose; and finally we plunged them again into very clean water. We thus cut the Gordian knot, and were on the right track.

In fact, on again repeating Mr. Dutrochet's experiments, with that minute care as to cleanliness that we had observed to be absolutely necessary, we saw crumble away, one after another, all the pieces of the scaffolding that this master had with so much trouble built up. The camphor moved in all our vessels, of glass or metal, and of every form, at all heights. The immersed bodies, such as glass tubes, table knives, pieces of money, etc., had lost their pretended "sedative effect" on a pretended "activity of the water," and on the vessels that contained it. The so-called phenomenon of habit "transported from physiology into physics," no longer existed.

The likening of the apparatus employed to obtain motions of camphor upon water, with the entirely physiological apparatus by means of which nature effects a circulation of the liquid contained in the internodes of Chara vulgaris, had proved a grave error that was to be erased from the science into which it had been introduced by its author with entire good faith. The true cause of life had not then been unveiled, and the new agent designated as diluo-electricity vanished before the very simple and authentic fact that camphor moves rapidly upon the surface of very pure mercury, in which no one would assuredly suppose that that volatile substance could dissolve.

Mr. Dutrochet attaches great importance to the manner in which the water is poured (with or without agitation) into the vessel with which the experiment is performed. The matter is in fact of little or no importance, and to prove this, it is only necessary to employ a test glass (see figure) provided with a lateral tube, A, that terminates in a lower tubulure, B, above which there is a contraction, C. Upon pouring water into the lateral tube until the level reaches D, and placing a particle of camphor on its surface, the camphor will be seen to continually move about, even when the liquid has reached the upper edge of the vessel. To reduce the level to various heights, it is only necessary to revolve the tube in the cork through which it is fitted to the tubulure. In proceeding thus, agitation or collision of the water is avoided; and yet if the test glass is very clean, the camphor will continue to move at every level of the water.

But, some one will doubtless say, how do you explain the stoppage in the motions of the camphor on the surface of water contained in vessels that are not perfectly clean? Before answering this question, let us say in the first place that the cause of the motions under consideration is due to nothing else but the evaporation of this concrete oil--to effluvia that escape from all parts and that exert upon the body whence they emanate a recoiling action exactly like that which manifests itself in an aelopile mounted upon a brasier, or, better yet, in the explosion of a sky-rocket. A portion of these camphory vapors, as well as a small portion of the camphor itself, dissolves in the water and forms upon its surface an oily layer which is at first very slight, but the thickness of which may increase in time until it becomes (especially if the vessel is narrow) a mechanical obstacle to the gyration of the small fragments of camphor that it imprisons, and whose evaporation it prevents. Now, as this layer of volatile oil may and does evaporate, in fact, after a certain length of time, the camphor then resumes its gyratory motions; but there is not the least reason in the world for saying on that account that it "has habituated itself to the cause which had at first influenced it, and that, too, in modifying itself in such a way as to render null the influence of a cause that has not ceased to be present" (Dutrochet, l.c.., p. 50).

We have been enabled to convince ourself of the existence of this oily layer of camphor when it was of a certain thickness by introducing under the water on which it, had formed, a few drops of sulphuric ether whose sudden evaporation produced sufficient cold to instantaneously congeal the layer in question and thus render it perfectly visible to the eye. The slight layer of greasy matter that habitually lines the sides of vessels from whence no effort has been made to remove it, produces effects exactly like those of the oil of camphor, that is to say, that in measure as it becomes thicker it likewise arrests the motions of the concrete volatile essence.

This is precisely what happens in a test-glass in which we see the camphor in motion become immovable if the level of the water be raised a few centimeters, and, more especially, if it be raised to the upper edge of the apparatus. In its slow ascent the liquid licks up, so to speak, the oily layer that lines the inner surface of the vessel, and this material spreads over the surface of the water and forms thereupon a layer which, in spreading over the bit of camphor itself, prevents its evaporation, and, consequently, its motions. The existence of the layer under consideration cannot be doubted, since it is made to disappear by causing the water to-overflow from the edges of the vessel, and, more easily still, by spreading a piece of filtering paper over the liquid in which the camphor is in a state of rest. As soon as the paper is removed (without the water being touched by the fingers, it should be understood), the camphor resumes its motions and afterward continues them at all levels.

The fingers themselves, provided they are very clean, have no power to stop the gyration. The following experiment, which is easy to repeat, is an unquestionable proof of this.

Wash carefully the middle finger with aqua ammonia, and afterward with plenty of water, and then dip it into a drinking glass in which a fragment of camphor is rapidly moving, and the gyration will not be stopped. But it will be made to stop instantly if the finger in its natural state (that is, covered with the fatty substances that ordinarily soil the fingers, especially in summer) be dipped into this same glass.

Movements Of Camphor Upon Mercury

In order to study the motions of camphor, mercury possesses, as compared with water, a great advantage, and that is that we can easily assure ourselves of the degree of cleanliness of this metal by means of the condensed breath. The vapory-deposits thereon in a uniform manner if the mercury is perfectly clean, but forms variously shaded and more persistent spots if it is soiled by foreign bodies But it is extremely difficult to clean mercury completely. To do so Mr. Boisgiraud and I take distilled mercury and leave it for a long time in contact with concentrated sulphuric acid, taking care to often shake the mixture. Then, after removing the greater part of the acid, we throw the metal into a vessel containing quick lime in powder, and finally pass it through a filter containing a few holes in its lower part.

Purified by this process, mercury not only permits of the motions of camphor on its surface, but renders visible the traces of the vapors that escape from it, and which resemble small tadpoles with a long tail that are endowed with very great agility. Nothing is more curious than to see the particle of camphor successively ascend and descend the strongly pronounced curves presented by the mercury near the sides of the vessel that contains it. On raising the temperature of the metal slightly, the motions of the camphor on its surface are accelerated, and the same effects occur with water that has been slightly heated.

The experiments that we have just called attention to show what importance slight impurities may have upon certain results. "They prove," says our learned colleague Mr. Daquin, "that there exists upon polished substances an imperceptible coating of those fatty matters which serve to-day to explain Moser's images." We find therein also a manifest proof and a rational explanation of those grave errors into which the presence of these fatty matters, that have hitherto been scarcely suspected, led so clever and so distinguished a scientist as the illustrious discoverer of endosmosis.--N. Joly, in La Nature.