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is either a gas or composed of gases. The last is the truth. What is the meaning of the term oxygen? The acid former. The term oxygen gas when applied to the gas which constitutes {th of atmospheric air is not strictly correct, because hydrogen and chlorine when chemically combined form muriatic acid, a very powerful acid, and hence hydrogen is an acid former as well as oxygen. How is oxygen gas prepared ? By applying a strong heat to the black oxide of manganese contained in an iron retort, and collecting the gas over water in the pneumatic trough : red oxide of lead, the peroxide of mercury, nitre, and the chlorate of potash, also yield oxygen gas when heated. Very pure oxygen gas is also obtained by placing cabbage leaves in water under a bell-glass and exposing them to the sunshine. The bubbles of air on aquatic plants growing in ponds or lakes are composed of pure oxygen gas. Mention some of the properties of oxygen gas. It is a powerful supporter of combustion; phosphorus burns in a jar of oxygen gas with great splendour, forming phosphorie acid ; and sulphur with a purple flame, forming sulphurous acid gas; red hot ste wire or the main-spring of a watch emits brilliant scintillations, and oxide of iron is the result. Hence oxygen gas is a powerful supporter of combustion, forming oxides or acids with the combustible according to circumstances. It is also necescary to support vegetable and animal life. What two gases constitute atmospheric air ? Oxygen and nitrogen gases. Every 100 cubic inches of atmospheric air contain 80 of nitrogen and 20 of oxygen ; but besides these gases there is always a trace of carbonic acid gas. If oxygen gas be respirable, what isæthe use of the nitrogen gas which forms such a large constituent of atmospheric air! It acts as a diluent. Did the atmosphere consist entirely of oxygen gas a single spark

would produce a conflagration-animal life would soon be destroyed from the intense action which the respiration of oxygen would excite, until at last nothing of this globe would remain but its ashes. In an atmosphere of nitrogen gas neither vegetables nor animals could ever have existed; but in an atmosphere composed of these two destructive elements in proportions such as we find in the air which surrounds this world, the order of the universe is preserved, and the life of man runs equably its allotted period of threescore and ten years. How is nitrogen gas procured? Set fire to a piece of phosphorus placed on a stool over water, and put an empty vessel over the burning phosphorus : the phosphorus unites with the oxygen of the atmospheric air contained in the vessel ; phosphoric acid is formed, which is dissolved by the water; and nitrogen gas remains. In this experiment the phosphorus must be more than 4th of the depth of the glass from the surface of the water, because by the consumption of the oxygen gas which the atmospheric air contains, the water rises to this height in the vessel, proving incontestibly that the oxygen gas in atmospheric air is---th of the whole.

What are the properties of nitrogen? They are all negative: it is incombustible, irrespirable, and a non-supporter of combustion. It is colourless, inodorous, and perfectly elastic. Are there many compounds of nitrogen? Yes; protoxide of nitrogen, deutoxide of nitrogen, hyponitrous acid, nitrous acid, and nitric acid. How is protoxide of nitrogen or laughing gas procured! By applying heat to the nitrate of ammonia. How is the nitrate of ammonia produced ? By pouring dilute nitric acid on the carbonate of ammonia carbonic acid is evolved, and nitrate of ammonia remains in solution. In forming a solution of nitrate of ammonia great care must be taken that the solution is neutral. This can easily be discovered by cabbage test paper. When the ammonia is in excess a drop of it will stain the test paper green, and if the acid predominates the paper will be stained red by a drop of the liquid. When a solution of nitrate of ammonia is boiled and then allowed to cool, beautiful acicular crystals are formed. What is the character of laughing gas ? It is a powerful supporter of combustion, but not so much so as oxygen gas. It is colourless, permanently elastic, respirable, and has a sweetish taste. When inhaled it acts powerfully on the system ; the circulation is increased, and a great tendency to muscular exertion and involuntary laughter is induced. How is deutoxide of nitrogen formed ? By pouring dilute nitric acid in copper filings. A portion of the nitric acid is decomposed, part of its oxygen unites with the copper, forming an oxide of copper, which again combines with a portion of the nitric acid, forming nitrate of copper, which remains in the retort. The deutoxide of nitrogen evolved is obtained from the portion of the nitric acid which has been decomposed. What is the test of deutoxide of nitrogen? Orange-coloured fumes are produced when it comes in contact with atmospheric air: the reason is this; the deutoxide extracts oxygen gas from the atmospheric air, and nitrous acid gas results. Can atmospheric air be analysed by deutoxide of nitrogen? Yes; let a jar be taken, the contents of which, by marks on the side, is divided into seven equal parts; let five of these be filled with atmospheric air, and the other two with water, the mouth of the jar being under water in the pneumatic trough; pass into this vessel as much deutoxide of nitrogen as is equal in bulk to two parts, that is enough to fill the jar with gas were there no condensation and absorption, five parts being already occupied with air; the jar instead of being filled with gas after this addition will be emptier than before, for

the water will rise, and the residual gas, which is pure nitrogen, will only occupy four parts.

A more striking experiment can be performed with oxygen gas and deutoxide of nitrogen. If one part of oxygen be mixed with two of deutoxide of nitrogen over water, almost the whole of the gases disappears.

What are the other characters of deutoxide of nitrogen? It is irrespirable, a feeble supporter of combustion, and a mixture of equal parts of this gas and hydrogen burns away silently with a lambent flame. How is nitric acid formed ? By pouring sulphuric acid on nitre, applying heat, and condensing the fumes in a cool receiver. Give the rationale of this process. Nitre is a nitrate of potassa ; the sulphuric acid decomposes the nitre, nitric acid is evolved and bisulphate of potassa remains in the retort. What are the tests of nitric acid ? When dilute nitric acid is poured on tin or mercury orange-coloured fumes are emitted, and when mixed with muriatic acid aqua regia is formed, which is a solvent of gold.

PHYSIOLOGY.

On the importance of the study of Physiology as a

branch of liberal education. The term Physiology is derived from two Greek words, one of which qúois nature, and the other hógos a discourse, an account of, literally a discourse about natural powers ; but, as now used, it applies exclusively to the doctrine of the uses or functions of the different constituent parts of beings endowed with the principle of life. As applied to the vegetable kingdom, it is called

vegetable physiology; to the lower animals, comparative physiology; and to man, human physiology. In all of these instances, however, the objects of physiology are the same, viz. the exposition of the mechanism and laws by which the various functions which characterize living bodies are carried on, so as to fit each individual for the particular sphere in which the Creator intended it to exist. Physiology, or the history of the functions which characterize living beings, is thus a subject of peculiar interest; and human physiology is as important in its practical consequences as it is attractive to rational curiosity. In its widest sense it comprehends an exposition of the functions of the various organs of which the human frame is composed ; of the mechanism by which these are carried on; of the relations to each other; of the means of improving their development and action ; of the purposes to which they ought severally to be directed; and of the manner in which exercise ought to be conducted so as to secure for the organ the best health, and for the function the highest efficiency. A true system of physiology comes thus to be the proper basis not only of a sound physical, but of a sound moral and intellectual education, and of a rational hygiene; or in other words, it is the basis of everything having for its object the physical and mental health and improvement of man; for so long as life lasts, the mental and moral powers with which he is endowed manifest themselves through the medium of organization, and no plan which he can devise for their cultivation, that is not in harmony with the laws which regulate that organization, can possibly be successful. That branch of education which applies to the study of our own bodies and the laws which regulate health, is perhaps the most important study, next to that of religion, which exists: nay, it may be said to be so inti

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