534 Mr. C. Tomlinson on the Motions of Eugenic Acid 



present. The pure hydrocarbons of these oils have a much less 

 retarding effect, and the more volatile ones scarcely prolong the 

 duration of the eugenic acid. When a drop of Persian naphtha 

 was placed on the same surface with the eugenic-acid disk, the 

 duration of the latter was extended to 20 minutes ; with oil of 

 cajuput 35 minutes ; with essential oil of nutmeg 52 minutes ; 

 with paraffin oil 90 minutes; with oil of pepper 180 minutes; 

 and with oil of lavender the eugenic acid had not disappeared 

 after two days, although the 2 ounces of water were increased to 

 4 ounces on the second day. 



In such cases the duration of the eugenic acid is but small if 

 the oil placed by the side of it is very volatile and but little 

 soluble in water, as in the case of some of the pure hydro- 

 carbons of the essential oils. Some of the oils themselves 

 form films and prevent contact between the eugenic-acid disk 

 and the water; in such case solution is no longer possible, and 

 the acid disk has an indefinite duration as in air. In other 

 cases — with oil of lavender, for example, where a film is formed, 

 a resinifying action sets in, and not only is the disk of eugenic 

 acid displaced, but its resinification is apparenly accelerated. 

 Hence its remarkable duration. 



To describe the behaviour of each oil that was tried on water 

 in the presence of the eugenic-acid disk, would occupy too much 

 space ; but I may note down a few. Of course for each observa- 

 tion a clean capsule and fresh water (2 oz. of distilled) were used. 

 While the eugenic acid was in vigorous action on the water, the 

 surface was touched with a drop of oil of turpentine hanging 

 from the end of a glass rod. The turpentine flashed into a film 

 that covered the whole surface, but it entirely avoided the 

 eugenic-acid disk. The latter was instantly struck motionless, 

 and formed a well-shaped double convex lens; but it had a 

 clear annular space around it free from the turpentine film. In 

 a few minutes, however, the acid disk resumed its activity and 

 invaded the turpentine film, cutting its way through it, while 

 the resinified particles of the turpentine soon formed currents 

 with the disk. When a drop of cubebs hydrocarbon was placed 

 on the surface it did not spread, but formed a flattened disk, and 

 immediately stopped the pulsations of the acid disk, which was 

 at least an inch away from it. The acid disk sailed about, and 

 by its influence indented the cubebs disk so as to make the latter 

 kidney-shaped, a result not uncommon when the oils flatten 

 down into disks. A fragment of camphor will do the same, as I 

 have already noticed*. In a few minutes some remarkable 

 twitchings came over the eugenic-acid disk, and active pulsations 

 were resumed. The disk then boldly attacked the cubebs disk, 

 * In my "Experimental Essays" a figure representing this effect is given. 



