Lessons in elementary chemistry: inorganic and organic / by Sir Henry E. Roscoe.

  • Roscoe, Henry E. (Henry Enfield), 1833-1915.
Date:
1892
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Licence: Public Domain Mark

Credit: Lessons in elementary chemistry: inorganic and organic / by Sir Henry E. Roscoe. Source: Wellcome Collection.

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    found in nature, which he can control and vary. Hence chemistry is called an experimental science. In thus in- vestigating all the materials within his reach, whether solid, liciuid, or gaseous, whether contained in the earth, sea, or air ; whether belonging to the animal or to the vegetable creation, the chemist finds himself able to divide substances into two great classes : (i) Co.MPOUXi) Sui!ST.\NCES—those which he can split up into two or more essentially different materials : and (2) Element.s or .Si.MPLE Sup.st.vnces— those which he has not been able thus to split up, and out of which nothing essentially difterent from the original substances has been obtained. Compound bodies are made up of two or more elementary substances chemically combined with each other ; thus sulphur and copper are elementary bodies ; out of each of these nothing different from sulphur or copper can be obtained ; whereas, when the two bodies arc heated together, a compound is formed from which both of the original ele- mentary constituents can at any time be prepared. Water is a compound body—it can be split up into two elementarv gases, hydrogen and oxygen ; common salt, again, is a com- pound of a gas (chlorine) with a metal (sodium) ; and lime- stone, clay, sugar, and wax may also serve as examples of com- pound bodies : whilst phosphorus, charcoal, iron, mcrcur)-, and gold may be mentioned as belonging to the class of simple substances. The following experiment well illustrates the I decomposition of a compound into two simple substances. A small quantity of the red powder called mercury oxide is 1 introduced into a test-tube, and heated in a gas llaine ; when 1 hot, the oxide gradually decomposes, a grey dc])osit of me- itallic mercury in small globules collect upon the cooler parts of the glass, whilst the tube becomes filled with colourless oxygen gas, whose presence can be demonstrated by the rekindling of a glowing chi|) of wood plungetl into the tube. On continued heating the whole of the red powder is found to be split up into the two elements, mercury and oxygen, which together weigh e.xactly as much as the red oxide from which they were obtaineil. I he elementary boilies, lor the sake ol convenience, arc arbitrarily divided into two classes, the metals and the non- metals. In the lirst are placed elements such as gold, iron.