formed under different circumstances. 179 



of water weighing 2*10 grains. This is therefore the weight of 

 the maximum drop formed on a flat surface, and it will be seen 

 that it very nearly coincides with the weight of the drop formed 

 upon a surface seven-tenths of an inch diameter. The drop in 

 this case is always formed at the centre of the surface, this being 

 the centre of the greatest molecular attraction amongst the liquid 

 particles. 



It will be observed that the drop formed in this manner is 

 considerably less than that which is formed in the tubes, the 

 reason of which is too apparent to require any explanation. 



The weight of a drop of liquid, other things being the same, is 

 diminished by an augmentation of temperature. "With a tube *3 

 inch diameter, the weight of a drop of water at 40° E. was found 

 to be 1*65 grain; whereas at 150° it was found to be only 1*45 

 grain, that is, the decrement of weight due to 110° was one-fifth 

 of a grain ; and so on to other temperatures. The decrements 

 of weight due to the temperature T were found to be closely ex- 

 pressed by the formula *0018 (T — 40) ; so that the weight of a 

 drop of water, at different temperatures, formed in a thin tube 

 of J) diameter will be expressed by the formula 



w 



= {5'5--006(T-40)}D. 



Independently of density, the chemical composition of a liquid 

 affects the iveight of its drop in a remarkable manner. Most acids, 

 alkalies, and alkaline salts diminish the weight of the drop. A 

 little potassa added to distilled water sensibly reduces the weight 

 of the drop. Strong sulphuric acid, having a density about 

 1J times that of water, under the same circumstances gives 

 a drop considerably less than that of water. Nitric acid, with 

 a density about 1^ times that of water, gives a drop of about 

 four-fifths of that of water. Spirits of wine, having a specific 

 gravity of '957, gave a drop of only about one-half of that of 

 water; and this spirit, diluted with sixteen parts of water, 

 making its density very little less than that of water, gave a drop 

 weighing less than six-sevenths of that of pure water. Olive oil, 

 having a specific gravity of *91 76, gave a drop of only about one- 

 half of that of water. Liquids having a low degree of fluidity 

 and a high cohesive attraction amongst their particles, such as 

 molasses, solutions of soap, starch, &c, all gave drops consider- 

 ably less than that of water. Hence it appears that where the 

 molecular force of cohesion is greatest, cceteris paribus, the weight 

 of the drop is least, and conversely. 



The weight of the drop of pure water being 2*84 grains, the 

 weights of a drop of the following solutions, having the same 

 specific gravity, viz. 1*190, were found to be, — chloride of sodium, 

 3*30 grains ; solution of sugar, 3-06 grains ; carbonate of soda, 



N 2 



