A College Text-Book of Chemistry

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1908 edition. Excerpt: ...of the increased quantity of free chlorine present. The decomposition is gradual, and, for any given temperature, the amount of decomposition is constant. This kind of decomposition, called dissociation, has been studied carefully, and is found to be capable of explanation by the aid of the kinetic theory of gases. In a later chapter this subject will be discussed, and a number of other examples will be given. Owing to this decomposition under the influence of heat the specific gravity of the vapor of phosphorus pentachloride is not what it should be, if the formula is PC16. On the other hand, the specific gravity of the vapor of the trichloride leads to the formula PCI, and that of the oxychloride to the formula POC13. The apparent anomaly presented by the pentachloride is easily understood. When a molecule of the compound is converted into vapor, or is heated to a sufficiently high temperature, it is broken down in accordance with this equation: PCI, = PCI, + C12. From the one molecule, therefore, two gaseous molecules are obtained. Consequently the vapor formed occupies twice as much space as it would if there were no decomposition. It follows that the specific gravity of the vapor must be only half what it would be if there were no decomposition. When the compound is converted into vapor in an atmosphere of phosphorus trichloride, the decomposition referred to does not take place, and, under these circumstances, the specific gravity is found to be in accordance with Avogadro's law, and with the formula PC1S. This case is a particularly interesting one, as it has played an important part in the discussions in regard to the validity of Avogadro's law. Treated with water phosphorus pentnchloride first gives the oxychloride and...