An introduction to modern scientific chemistry by unknow

Author:unknow
Language: eng
Format: epub
Tags: Chemistry
Publisher: New York, D. Van Nostrand company
Published: 1901-03-25T05:00:00+00:00

Aqua Regia. We have just learned that gold and platinum are insoluble in nitric acid; there is no single acid which dissolves these metals, but a mixture of nitric and hydrochloric acids brings them into solution: as the alchemists called gold the king of metals, they gave the name aqua regia to this mixture. Nitric acid (HNOs) is very rich in oxygen, and hydrochloric acid (HCI) consists of hydrogen and chlorine; when these two are mixed, the oxygen of the nitric add exerts an oxidising action on the hydrogen of the hydrochloric acid, combining with it to form water, so that the chlorine becomes available. We know that chlorine is extraordinarily active^or, to use a better expression, that chlorine possesses much chemical energy; hence we are not surprised that the chlorine, as it is produced in the nascent state, should attack gold arid platinum. If a solution of gold or platinum in aqua regia is evaporated to dryness, gold chloride or platinum chloride is obtained. These salts dissolve in water very easily.

We must juat mention that it has been found, in recent years, that a aolution of potassium cyaoide (which substance will be considered when we come to the compounds of carbon) dissolves gold, but not platinum. This method of e^rtracting gold from the finely powdered rock is now used in South Africa, almost to the exclusion of all others.

Explosives.

We know that the salts of nitric acid are very rich

in oxygen. It is its richness in oxygen that has caused

O^K

178 INTRODUCTION TO MODERN CHEMISTRY.

potassium nitrate—a substance which does not differ in appearance from a thousand other white salts—to have a greater influence on the history of peoples than any other chemical compound. For the history of a people has often depended on a battle won or lost, and it is this nitre which has helped to decide innumerable battles of the later middle ages and of modem times. Nitre has been the foundation of all sorts of gunpowder until very recently. For about fifteen years attempts have been made to replace powder made with potassium nitrate by smokeless explosives based on nitric acid.

The connection between nitre and gunpowder is as follows. A mixture of nitre with such combustible substances as charcoal, pitch, or sulphur continues to burn once it has been ignited. In distinction to ordinary combustibles, such a mixture does not require to get oxygen from the air for its combustion, but it finds the required oxygen in the nitre. Hence such a mixture can do what an ordinary combustible body cannot do: it can burn in an enclosed space without the entrance of oxygen from outside; it can burn under water, for instance.

We have here a mixture of 25 parts ordinary gunpowder, 50 parts nitre, 40 parts charcoal, and to parts sulphur, which has been moistened with spirit (this removes the risk of explosion during the rubbing), well mixed by rubbing, packed as tightly as possible into a paper covering, and kept for some time in a chamber at lto°, whereby the spirit has been removed.

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