20 MOTION OF THE JUICES OF THE ANIMAL BODY. 



phenomena connected with chemical affinity, are affected, altered, increased, or 

 destroyed by causes quite analogous. 



After heavy rains, the water of many rivers becomes turbid and opaque from 

 the presence of a fine clay. These suspended particles of clay are so fine as to 

 pass through the finest filters ; and their adhesion to the water is so great, that 

 such water does not clear after standing for weeks. The water of the Yellow 

 River, in China, possesses, during the greater part of the year, this character ; and 

 from the French missionaries, we know that alum is universally employed in Pekin 

 to clear it. In fact, if a crystal of alum be held in such a water only for a few 

 seconds, we observe the sediment separating in large thick flocculent masses, the 

 "water becomes transparent, and hardly a trace of dissolved alum is to be detected 

 by the most delicate re-agents. Chemistry is acquainted with a number of similar 

 means for causing the separation from liquids of suspended precipitates.. 



In these cases we see, that by an alteration of the quality of the water, produced 

 by what we call mere mixture with a foreign body, its power of combining with 

 Others is destroyed or weakened. 



It is well known that the force with which, in a solution, the particles of the 

 liquid and those of the dissolved body attract each other, is very unequal in different 

 cases ;* and in this point of view the action of many solid bodies on saline solu- 

 tions is very remarkable ; inasmuch as it is thereby demonstrated, that the mole- 

 cular force, which determines the phenomena of cohesion, and the moistening of 

 solid bodies by liquids appears to be identical with chemical affinity, since chemical 

 compounds can be decomposed by means of it. Professor GRAHAM has shown 

 fliat common charcoal, deprived by acids of all soluble ingredients, completely 

 removes the metallic salts or oxides from solutions of salts of lead, tartar emetic, 

 ammoniated oxide of copper, chloride of silver in ammonia, and oxide of zinc in 

 ammonia ; while other solutions, such as that of sea salt, suffer no such change. 

 A bleaching solution of hypochlorite of soda loses entirely its bleaching properties 

 by agitation with charcoal ; and iodine can be removed by the same means from 

 its solution in iodide of potassium. Every one is familiar with the action of finely- 

 divided platinum, with that of silver on the deutoxide of hydrogen ; as well as 

 with that of charcoal on dissolved organic matters, coloring matters, &c. ; and 

 freshly-precipitated sulphuret of lead, sulphuret of copper, and hydrate of alumina, 

 resemble the latter in their action. Many organic substances, such as woody fibre 

 and others, act on dissolved matters, such as salts of alumina or of oxide of tin, 

 just as charcoal does; and we know that the application of mordants in dyeing, 

 and dyeing itself depend on this very property. The adhesion of the solid coloring 

 matter to the cloth which is died with it is the result of a chemical affinity so feeble, 

 that we hardly venture to give the molecular force that name in this case. From 

 a piece of woollen cloth dyed with indigo, the indigo is completely separated, by 

 mere beating, continued for some time, with a wooden hammer, so that the wool 

 is at last left white. 



The surface of the solid body exerts, as these facts prove, a very unequal attrac- 

 tion on the molecules, which come in contact with it. 



Researches on capillary attraction have shown that, with one and the same 

 liquid, water, for example, the substance of the solid body has no influence on 

 Ihe height to which the liquid rises on it. On slices of box-wood, clay-slate, or 

 glass, the rise of the liquid above the surface of the water is the same exactly as 

 in the case of a plate of brass. (HAGEN.) In the case of other liquids, the par- 

 ticles of which are entirely homogeneous, the same law may be assumed in theory ; 

 but with such liquids as contain foreign bodies in solution, a change in the capillary 

 attraction must be produced by the presence of these bodies, because by them the 

 cohesion of the liquid is altered ; and, perhaps, still more because the liquid 

 ceases to be homogeneous, when the attracting wall has a stronger affinity for the 

 particles of the dissolved body than for those of the solvent. 



From what has been stated, it appears, that the mixture of two liquids is the 

 result- of a chemical attraction ; for how otherwise could chemical compounds, 



* Action of solids on dissolved matters. 



