Mr. C. Tomlinscm on the Cohesion-Figures of Liquids. 193 



with the lower series and gradually ascending-. The colours 

 cover the film in irregular bands, producing exquisite harmony. 

 Suddenly the film opens into holes, which, in the midst of the 

 colours, have a striking effect. The colours disappear with the 

 film, leaving a network or lace-pattern, the holes becoming- 

 ovoid and many-sided, and the colour a beautiful steel-blue. 



A charming effect may be produced by holding a drop of tur- 

 pentine from the end of a glass rod over the blue lace-pattern. 

 The vapour condensing upon the lines, causes them to swell out 

 and apparently to crowd closer together, while the colour becomes 

 changed to a silvery white. 



The effects above described succeed each other much more 

 rapidly on a bright warm day than on a damp or dull one, — a 

 remark that equally belongs to many other films. 



The film of ol. sabinae has the double row of bosses, and pre- 

 sents the other phenomena of the turpentine film, only modified 

 in various particulars, which enable it to be distinguished from 

 all other films. 



The same remarks apply to oils of juniper, cajeput, bergamot, 

 lemon, and some others. 



In all these cases the characteristics of the turpentine film are 

 distinctly recognizable. 1. They all open with a flash of rain- 

 bow colours. 2. They all have the double row of bosses about 

 the edge, i. e. a very minute beading at the edge, and a larger 

 beading just within it. 3. They all display bright iridescent 

 colours as they become thinner by evaporation. 4. They all 

 open into holes; and 5. They all form a network which lasts 

 for a long time. 



No two of these oils, however, are precisely alike in passing 

 through these changes, except perhaps the oil* of turpentine and 

 the oil of spike ; indeed it is often difficult to distinguish between 

 these two oils, from the circumstance that the commercial oil of 

 spike is composed of a mixtureof three parts essential oil of turpen- 

 tine and one part oil of lavender. Some oils do not give the same 

 rainbow tints in opening as others. In some the double row of 

 bosses at the edge is on a little larger scale than in the others. 

 In some the colours that come over the film are brighter and 

 more metallic than in others. In some the holes are smaller and 

 more numerous than in others : the oil-of-juniper film, for 

 example, displays a multitude of holes like needle-points closely 

 crowded together. And lastly, the network is finer in the film of 

 some oils than in that of others. In some cases this network 

 resembles a vegetable structure, as in that of ol. myristicaj, 

 where the lines are like long branches of very delicate moss, laid 

 down so as to form a tolerably regular pattern. 



Other groups of liquids also present interesting resemblances 

 Phil. Mag. S. 4. Vol. 23. No. 153. March 1862. O 



