186 Mr. C. Tomlinson on the Cohesion-Figures of Liquids. 



Neither silver nor sulphur could be detected in the metal. 



It would seem from these results that the dark-coloured guns 

 are produced from the commercial copper of the country, with the 

 addition perhaps of a very small proportion of zinc. The front 

 part of the gun examined appears to have been cast of a metal 

 somewhat different from and inferior to the remaining portion. 

 In several parts of the gun the metal was in an exceedingly 

 porous condition, and appeared to have been cast at a very low 

 temperature. Some portions contained many cavities lined with 

 the oxidized metal. 



XXVII. On the Cohesion-Figures of Liquids. By Charles Tom- 

 linson, Lecturer on Science, King's College School 3 London*. 



IN a paper read before the British Association last year, and 

 inserted in the October Number of this Journal, it is shown 

 that when a drop of an independent liquid (i. e. not a solution) 

 is gently deposited on the surface of another liquid (such as 

 water), it flattens out into a peculiar and characteristic figure, 

 which is the resultant of its cohesive force, its density, and the 

 adhesion of the surface. 



The principle of these cohesion-figures (as I name them) being- 

 established, facts and details may be multiplied to almost any 

 extent. I have already ascertained the figures of about one 

 hundred liquids, and have made some progress in establishing 

 their value in analysis, and in the detection of adulteration, to 

 which they seem well fitted. It was not my intention to have 

 written again on the subject until the investigation had advanced 

 further towards completion; but inquiries having been made 

 consequent on failures in the production of these figures, I may 

 perhaps be allowed on the present occasion to state a few more 

 particulars. 



The sources of failure are chiefly three: — 1. Want of purity 

 in the vessels used. Glass, &c. exposed to the air contracts an 

 organic film, so that when a vessel is filled with water, the sur- 

 face of the latter becomes covered with a portion of such film, 

 and this prevents adhesion between the water and the drop de- 

 posited on it. The vessels must be washed from time to time 

 with strong sulphuric acid, and rinsed after every experiment 

 with a strong solution of caustic potash and then with water. 

 2. Want of care in delivering the drop. The drop must not be 

 allowed to fall on the surface, but be gently delivered to it from 

 the end of a glass rod, or from a dropping-tube. 3. Want of 

 care in preserving the surface of the water tranquil. After the 



* Communicated by the Author % 



