Physiological histology, methods and theory / by Gustav Mann.

  • Gustav Mann
Date:
1902
Catalogue details

Licence: Public Domain Mark

Credit: Physiological histology, methods and theory / by Gustav Mann. Source: Wellcome Collection.

    35/524 page 13
    THE FORMATION OF IONS The positive ion will induce in the water molecules surrounding it a negative charge, while the negative ion will induce a positive charge, and hence the effect of the negative and positive ions upon one another is weakened, as now they are attracted by that induced charge to which they themselves previously have given rise. Charge of lcat-ion. Induced charge in solvent. Charge of an-ion. + - + - What leads to the original dissociation of an electrolyte is difficult to say, but owing to the slight dissociation of water which exists normally (see p. 21), it may be assumed that the hydrogen kat-ion or the hydroxyl an-ion starts the dissociation of the electrolyte, and this change having once started, spreads to the non-dissociated molecules of the electrolyte, owing to the induced charges in the solvent. The conditions under which ions are formed have been classified by Ostwald as follows : (a) An electrically neutral body splits up into equivalent quantities of positive and negative ions, as happens, for example, if anhydrous acids, bases, or salts come into contact with water ; thus HC1 becomes H' + Cb, and NaCl splits into Na+Cl'. (5) A neutral body abstracts from other ions present their electrical charge, to break up itself into free ions. When this change occurs the free ions, from which the electrical charge has been withdrawn, cease to be ions, as will happen if zinc displaces another metal, such as copper, from a salt, or if an acid radical, suclr as iodine, is displaced from an iodide by the stronger radical chlorine. (c) A neutral body passes into positive ions while simultaneously another neutral body is changed into an equivalent number of nega¬ tive ions, as happens, for example, if gold dissolves in chlorine water. Chlorine has normally a great tendency towards ion formation, but cannot satisfy this desire till it meets with another neutral body such as gold, which can become loaded with a positive charge. (d) Changes, as just described under a, b, and c, take place with neutral bodies containing radicals capable of holding different or multiple charges of electricity. Thus, if chlorine is passed through a solution of ferrous chloride, it can become a negative ion, because the divalent ferro-ions take up an additional charge of positive elec¬ tricity, becoming changed into the trivalent ferri-ions. A diminution of the negative amount of electrical charge will have the same effect as an increase in the positive amount; for if chlorine be led into a solution of potassium permanganate, the ions of which are 2K’, and the divalent MnO/', chlorine ions are formed because the divalent MnO/' loses a negative unit, and is changed into the monovalent ion MnO/ of permanganic acid (HMnOJ, What is meant by the term hydrolysis is explained on p. 21, and the bearing of the changes described above under d on the pheno¬ mena of oxidation and reduction is discussed on pp. 68-70. It was mentioned on p. 10 that the electrical charge of a gram-ion of hydrogen amounts to 96,500 coulombs, and that the same amount
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