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376 THE PHOTOGRAPHIC NEWS. [August 7,1863. an instance of an action relating to photographic dealings which might not have been avoided had a clearly stated and duly stamped agreement been made at the outset. Stientifit 6ossiy. MOVEMENTS OF CAMPHOR ON WATER—NEW TEST FOR GREASE AND IMPURITIES. When small pieces of camphor are dropped on to the sur face of a glass of water several curious phenomena may be observed. They immediately commence to rotate, and move about with remarkable energy, varying sometimes in rapidity, but usually conducting their gyrations in a strange and erratic manner. This is an experiment which most of our readers must have seen performed at some time or other. In order to obtain the best effects, some precautions are neces sary : thus the camphor should be tolerably pure, the piece employed should be cut and separated from the larger lump with a perfectly clean instrument, and contact with the fingers should be scrupulously avoided. Moreover, the glass should be quite clean and the water pure. When these con ditions are satisfied, the phenomena are really very striking, and well merit more attention than is generally devoted to such things. Several physicists have observed these curious motions of camphor; amongst others may be specially named Mr. Tomlinson and Mr. Lightfoot. The former gentleman has been attracted more to the physical phenomena involved, in the movements, whilst Mr. Lightfoot has principally studied the chemistry of the subject. Each is of interest, but it is to some results recently found out in respect to the latter branch of inquiry that we desire at present to draw our readers’ attention. If, instead of using a torn or cut fragment from a lump of camphor, one or two fine crystals are detached with a clean needle-point from the cork of a phial in which camphor is kept, and these are let fall on to clean water, they at once begin to move about with wonderfully increased rapidity, darting away in various directions, as if shot from some miniature engine of propulsion ; or, as if endowed with life and a will of their own, they feared the searching eyes and magnifying lens of the ob server in their endeavours to find a hiding-place; each crystal quivering and rocking on the water with an apparent high degree of indignation at its forced contact with the humid surface. This fury gradually diminishes, and a regular dance begins with the various additional particles that may be introduced to the company. They select partners, to some of which they will seem to cling with pertinacity, whilstothers will either remain indifferent or, if attracted, will only stay a very short time in embrace, detaching and wandering again in search of more congenial floating associates. The explanation which Mr. Lightfoot gives of these movements is the emanation of a vapour from the volatile camphor. This vapour has a very low tension ; the water upon which it floats being capable of dissolving and diffusing this vapour more readily in certain directions of the crystalline axes, thereby removes sufficient vapour pressure at those points for the opposite side to drive about (by recoil) the nicely suspended particle. Thus, if we place on water several well- defined hexagonal plates and prisms of camphor, the mutual attraction of the particles will be noticed to be stronger in the direction of the angles of the hexagon, accompanied by a de cided preference for one of the axes, generally the longest in prismatic crystals. In certain positions two crystals of cam phor will attract each other, whilst in other situations there is a mutual repulsion. It will sometimes happen that two crystals of camphor may be thrown on the water and not have any tendency to locomotion. When this is the case a continual trembling or vibration will be noticed in the crystal. When two such stationary vibrating crystals come in contact by attraction, immediately an eccentric, irregular change of place takes place, as if the force agitating each previous to the grouping produced a new resultant force in obedience to which the combined crystals move. In our description of the method of separating and placing the camphor on the water, we laid some stress on the fact that everything should be quite clean, and that the fingers should not touch the camphor in any stage. The reason of this is obvious. If, whilst camphor is actively moving on water, the most minute particle only of cer tain greasy substances touch the water, instantaneously, as if by some magic shot, the camphor is deprived of all motion. The scene of previous activity is changed into the immobility of death. This curious property has been made use of by Mr. Lightfoot to detect grease in quantities so extremely minute as would appear almost fabulous. Thus, if we take a clean needle or pin, and only pass it through the hairs of the head, or cause it to touch the side of the nose or the surface of the forehead, and then insert the point of the needle just under the surface of the water, where camphor is rotating, it will instantly stop it; for camphor cannot be made to rotate on water containing the most infinitesimal portions of grease. Mr. Lightfoot lias made use of this test in a most ingenious manner to distinguish between the two different methods of dyeing cloth with madder and with garancine. It is difficult and often impossible for calico-printers and merchants to distinguish between the two, and as the garancine dye is more fugitive than the first, and also of less intrinsic worth, it is some times substituted for it. There is, however, a slight differ ence in the process of manufacture—madder-dyed goods are, in one stage of the process, passed through a solution of soap to fix the colour, whilst in garancine-dyed goods the soap is replaced by hypochlorite of lime. By proceeding as follows, it is easy to distinguish between the two kinds of dye :—Let camphor rotate on water in any convenient glass vessel, as previously described, then immerse a small strip of the cloth to be tested. If the rotation stops, we infer the presence of soap, and conclude it to have been dyed with madder. But if, on plunging in the small piece of cloth, the rotation is not stopped, we then arrive at the conclusion that garancine was the dyeing material used. This plan of testing is more decisive in doubtful cases, if the pieces of cloth are, with as little handling as possible, boiled, each in a small glass beaker, and, when cooled, bits or crystals of camphor arc dropped on the surface of each sample liquor. Possibly our readers may never require to test pieces of cloth for a particular dye in the above manner; but they can frequently make use of the test with advantage in detecting the presence of grease in materials which more immediately concern them. What more necessary, for in stance, than to have the cloths and leathers with which their glasses arc cleaned perfectly free from grease? and how fre quently are these important, though humble, adjuncts to the laboratory returned home by the laundress in a most unphotographic state of soapiness! A morsel of camphor in a glass of water will instantly show whether any cloth > s fit to give the final polish to a glass plate, by its not atrest ing the movements, or whether it is dangerously greasy, 88 shown by its stopping the rotations. Again, it is not so commonly known as it ought to be, that distilled water fre quently contains more than a trace of grease. Sometime this can be recognised by the odour; but if this does no* detect it, or if the photographer assumes that, because distil^ it must necessarily be pure, endless troubles and vexations may be entailed upon him, and fogging baths and stained plates will become the rule, instead of the exception. Before using the distilled water for any photographic purpose, 1 should always be tested by pouring a little into a wine 8la88 and then dropping a fragment of camphor on to the surface. The degree of purity of the liquid is at once shown by t he energy of the movements. So delicate is this test, that 110 author has proved the presence of grease in water taken on of the sea about a mile from the pier at South port (attributer to the sewage emptying itself near to the pier), whilst wa e taken out of the Irish Sea about sixty miles from SouthPo was perfectly free from any greasy matter whatever.