Lecture on Water.

Wairarapa Standard, Volume XVIII, Issue 1765, 30 November 1885, Page 3

Lecture on Water.

(Continued.) None of these experiments allow us to collect the oxygen from the water, for in all oases a substance has been used that combine with the oxygen aud set free the hydrogen, but there are various ways by which we can prepare a supply of oxygen gas. The readiest and beat way is by treating a substance called chlorate of potassium mixing with it a little black oxide of manganese. Each of these substances heated alone would give off oxygen, but wheu heated together the the oxygeu comes off at a much lowei temperature than if the substances were used singly. (Exp S.) To heat the mixture a retort or a florence flask fitted with a cork and delivery tube may be used. The oxygen gas may be collected in the same way as the hydrogen. After heating the mixture for some time oxygen gas comes off very freely. Collect about six jars of it for the various tests.

To find out the properties of oxygen let ns test it as we have tes’ed the other gases, with a lighted splint. (Exp 9.) Plunge the lighted splint into a jar of oxygen. Ton notice that the oxygen gas does not take fire like hydrogen, and it does not extinguish the light as hydrogen, nitrogen, and carbonic acid gas would do. On the contrary the further the splint is pushed iuto the gas the more brightly does the wood burn. Next withdraw the splint and blow out the flame, leaving only a slight red spark and again plunge the splint into the oxygen gas. Note that at once the flame starts into activity again, although the spark was almost extinguished. Oxygen is the great supporter of combustion. All ordinary burning is simply some element or other combining with oxygen. When we say of some substances that they will not burn, it amounts to saving that they will not in their present condition combine with oxygen. The following experiments show the quickness of brilliancy with which combustibles bum in pure oxygen, and such attractive experiments are useful in attracting and retaining the attention of the scholars.

Take first phosphorus (Exp 10). This substance barns readily in air and with a fairly bright flame, but note how much greater is the brilliancy of its flame in oxygon gas, and how rapid is its combustion. Note a'so the white fumes as in Exp. 3 of the first lecture. 'bese fumes being a compound of phosphorus consumes the oxygen. In thisexperi men? always dry the phosphorus by wrapping it in blotting paper and pressing it slightly, if the phosphorus be cot dried then in burnin? it will throw off heated sparks that may crack the jar. The following experiments shew flames of a beautiful color ; (Exp. 11). Burn sulphur in a small capsule in a jar of oxygen. The sulphur burns with a beautiful blue tiame. _ (Exp. 12 ) Mix powdered nitrate of strontium with powdered charcoal and barn the mixture in oxygen gas. It burns with a bright red flame. Compounds of strontium are often used to procure red lights. (Exp 13.) A mixture of one part of boracic acid (uot borax as printed in the syllabus) and three parts of charcoal burns in oxygen with a green flame. (Exp 11) A more striking experiment than any of these consists in burning iron wire in oxygen. A piece of iron wire or a watch spring is tipped with a piece of cork dipped in spirits of wine or kerosene. Light the cork and plunge the wire into a jar of oxygen. The iron burns as easily as paper does in common air. It is well to have a layer of sand and water in the bottom of the jar else the globules of melted iron falling may crack the jar. It is not alone as a free gas that oxygen has the power of encouraging combustion, (Exp 15.) Here is a dish containing nitre or saltpetre fused. Nitre is a compound of the three elements, potassium, nitrogen and oxygen, all of which have already been mentioned. Heat some powdered charcoal and throw it into the fused nitre. At once bright sparks arise from the combustion of the charcoal, the exygen leaving the potassium and nitrogen in order to combine with the charcoal.

Ogr last experiment to-day consists in bringing together or uniting the two gases hydrogen and oxygen to form water. (Exp 16.) Here is a stoat sodawater bottle into which I am now introducing enough hydrogen to fill two thirds of the bottle. The remaining third is now being filled np with oxygen. This bottle then contains these two gases in the proper proportions to form water. If left alone the two gases mix but do not combine, bnt if a flame be introduced into the mixture the gases combine with explosive violence. This bottle is a strong one, yet to prevent risk I shall wrap ronnd it this duster. On lifting the bottle and introducing a lighted splint you note the instant flash and exph sion. The hydrogen and oxygen have combined to form water which at first is in the state of steam, but soon condenses. A bottle full of the mixed gases will form but a few drops of liquid water, hence in this experiment but little result is found in the shape of water. In the next lecture we shall continue our study of water.