■126 Mr. C. Tomlinson on a new Variety of 



if not chemically pure, of the same liquid, produced in various 

 countries and under different conditions; (2) the examination 

 of such specimens, with the view of obtaining standard co- 

 hesion-figures ; and (3) the effect of admixtures of different 

 liquids in various proportions on such figures. I had already 

 taken considerable pains in ascertaining the figures of a number 

 of liquids ; and not being able to bestow the time required for 

 further investigation, even were I able to command the speci- 

 mens, it seemed best to lay the subject before such societies as 

 those named, many of the members and students of which had 

 remarkable facilities for carrying it out ; and besides this, as the 

 journals of those societies circulate largely among persons in- 

 terested in the possession of a ready test for determining the 

 purity of commercial oils and other liquids, the subject was 

 likely to attract the attention of practical men. 



Most of the figures described in my papers are produced by 

 placing a drop of liquid on the surface of chemically clean water 

 in a chemically clean glass; and the phenomena are confined to 

 the surface. If the drop be placed on any other surface than 

 water, such as sulphuric acid, acetic acid, alcohol, benzole, &c, 

 the figures vary, because the adhesive force, the diffusibility, &c. 

 vary. If the drop be considerably heavier than the liquid which 

 forms the adhesive surface, it will sink and diffuse more or less 

 through the body of the liquid, producing a new set of figures, 

 of great variety and beauty, which I propose to consider in the 

 present communication. 



A good typical example of this class of cohesion-figures by 

 submersion (not on the surface, as in the former experiments) is 

 furnished by a solution of cochineal in distilled water. Three 

 solutions were made, one with 15 grains, another with 20 grains, 

 and a third with 40 grains of cochineal, in one fluid-ounce of 

 distilled water. The solutions were filtered, and, after each had 

 run through, half an ounce of water was poured on the filter; 

 and three other solutions were thus obtained, and were kept 

 apart. A single drop of one of these solutions was delivered 

 from a pipette to the surface of water contained in a cylindrical 

 glass. A small quantity of a solution of alum or of oxalate of 

 ammonia had been previously added to the water for the pur- 

 pose of throwing down the lime; and even when distilled 

 water was used, the alum adds to the persistency and beauty of 

 the figure by its tendency to form a lake with the colouring 

 matter. 



As soon as the drop of cochineal solution falls beneath the 

 surface, it expands into a ring, sinks a short distance further, 

 and then becomes poised (see Plate IV. Cochineal, No. 1). The 

 more diffusive portions of the colouring matter stream upwards 



