Wells's principles and applications of chemistry; . ig. 74. * The difference in the strength of the affinity exist-ing between different substances may be easily illus-trated by the following experiment:—Dissolve a fewcrystals of acetate of lead {sugar of lead) in a smallquantity of water, and fill a phial with the solution. Ifa piece of zinc be now suspended in the liquid, it will,after a little time, become covered with a gi-ay coating,from which brilliant metallic spangles wUl graduallyshoot forth (see Fig. 74) somewhat in the shape of atree. These are pure lead, and the phenomenon is fa-mi
Wells's principles and applications of chemistry; . ig. 74. * The difference in the strength of the affinity exist-ing between different substances may be easily illus-trated by the following experiment:—Dissolve a fewcrystals of acetate of lead {sugar of lead) in a smallquantity of water, and fill a phial with the solution. Ifa piece of zinc be now suspended in the liquid, it will,after a little time, become covered with a gi-ay coating,from which brilliant metallic spangles wUl graduallyshoot forth (see Fig. 74) somewhat in the shape of atree. These are pure lead, and the phenomenon is fa-miliarly known as the lead tree. The effect thus pro-duced is due to the superior affinity of the zinc for theacetic acid combined with the lead, which causes thetwo metals to interchange places—i. e., the zinc combin-ing with the acid and entering into solution, and the leadbeing deposited in a metallic state, in place of the zinc. If the action be kept up sufficiently long, every particle of lead may be in this way with- diawn from the Questions.—What is the third characteristic of affinity ? What is the fourth ? Illus-trate this. Is the force of affinity always uniform f How may this be shown ? PEIKCIPLES OF CHEMICAL PHILOSOPHY. 161 yi. However mucli the properties and form of bodiesmay be changed by the action of chemical affinity, no de-struction of matter ever ensues—the weight of the pro-ducts of combination being always exactly equal to thatof the component elements before combination. By means of a simple experiment it may be shown that even although asubstance may, through the action of chemical affinity, vanish from our sight,it still continues to exist as a gas which has the same weight as the visiblesolid which furnished it. Into a glass flask, A, Fig. 15, of about 250 cubicinches capacity, which is provided with a brass cap and stop-cock, 10 or 12grains of gun-cotton are introduced. The air in the flask is then completelyexhausted by means of an air
Size: 1558px × 1605px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1860, booksubjectchemistry, bookyear18
