SATURDAY SCIENCE LECTURES.

Tuapeka Times, Volume XVII, Issue 1041, 14 May 1884, Page 3

SATURDAY SCIENCE LECTURES.

The second lecture of this series was delivered on Saturday last. Mr T. N. Watt was present, and rendered assistance to Professor Black. The lecturer stated that there is a variety of substances from which the chemist can obtain oxygen ; among others are oxide of mercury (Hg 0), chlorate of potash (KClOs), oxide of manganese- (MnOa), water (Ha U), chloride of lime (CaCl ), and all the nitrates, chlorates, manganatea, and permanganates. Permanganate of potassium possesses more oxygen than, it can retain. If dissolved^ in water it forms a violet solution, which, on being subjected to the action of sulphate of iron, parts with the excess of oxygen, and, losing color, becomes a clear liquid. To perform the experiment successfully a little muriatic acid should first be added. It is a law in chemistry that when you withdraw an element from a compound to form another compound, the resultant will be something entirely different from the original. When chloride of lime is used as a disinfectant, it similarly parts with its excess of oxygen, and organic impurities in its neighborhood are burnt up by contact with the liberated oxygen. Oxygen is colorless, tasteless, has no smell, and is invisible. Up till four yearo ago, it was not known to be convertible to the liquid state, 'but then some French and Swiss physicists managed, by the application of extreme pressure, at a low temperature, to liqwfy it. The same was done with hydrogen, and, in the same way, it has even been converte4 to the solid state. Now it is known that any gas may be under certain conditions converted to a solid. So readily does oxygen combine by combustion to form compounds that \ even the diamond, the hardest substance known, when heated will barn in it to form carbonic acid. Charcoal, hydrogen, phosphorus, sulphur, iron, lead, magnesium, and in fact most of the metals burn in the gas to form oxides. The non-metals in combination with oxygen form carbonic acid (0 O2 ), sulphur dioxide (S O2 ), sulphur trioxide (S O3 ), phoaphoric anhydride (Pa O2 ), and nitrogen pentoxide (N Os ) called acid oxides, as when they enter into combination with water they form acids. For example : SOa+ Ha 0 = H2SO4, the powerful acid, oil of. vitriol. The metals in combination with oxygen form potassium oxide (KaO), sodium oxide (Naa O>, quicklime (Ca 0), ferrous oxide (Fe 0), ferric oxide (Fea Os ), oxide of lead (PbO), and oxide of magnesium (Mg 0) called basic oxides ; the result of union of a basic oxide with an acid oxide, is a salt. For example : SOs + Ca O=Ca S O4 sulphate of lime, or gypsum ; and oOs+ Ca O=Ca 0 03 , carbonate of lime. There are soraa oxides, usually, of metals but some of non-metals, '"which,' being neither basic

nor acid oxides, are termed "neutral." Such are— water (H2 0), oxide of manganese (Mn Oa ) magrietic iron oxide (PeoO4), oxide of barium (BaO), nitric oxide (N 0), and carbonic oxide (C O). Gunpowder consist of 75 per cent of saltpetre, 12| per cent sulphur, and 12£ willow- wood , charcoal, all • the • ingredients being of the finest description and in the finest state of division. Gunpowder is only a mixture— not a chemical compound. Under the microscope, the bits of sulphur and saltpetre can be distinguished from, the charcoal by- their colors ; also when the mixture is boiled the constituent substances may be filtered out. The word " melts" has a double meaning, and for that reason should be avoided as far as possible in describing' processes in chemistry and physics; the words "fuse," and "dissolve " more exactly describe the two processes for either of which " melt " may stand. Ozone is a kind of oxygen. During a thunderstorm people often describe a sensation, by saying, that they "smell electricity in the air." What they perceive is the presence of ozone. Ozone may be developed from oxygen that has in it some vapour of ether, by stirring therein a heated glass-rod, or by suspending some phosphorus in an enclosed jar of atmospheric air. We may look upon ozone as three gallons of oxygen condensed into two gallons. It is now known that ozone is converted from the oxygen of the air by means of electricity during thunderstorms. Some time since, the English Parliament appointed a commission to investigate the whole subject of the pollution of the atmosphere about large cities. Sir Lyon Playfair was a member of the commission. Tests instituted simultaneously in the centre and on. the windward and leeward sides of such a city as Manchester revealed the fact that. large quantities of ozone pass into such a city in the atmosphere, but it is all converted in passing through their organic emanations. Ozone is usefulas a purifier of the atmosphere ; for it effects a removal of obnoxious and deleterious organic matter. Some physiologists assert that much ozone is hurtful to consumptive persons ; they assert that it is too strong for the lung 3of such people. The tests for ozone are — Blotting paper, moistened with emulsion of starch and potassic iodide, turns blue in the presence of ozone by its liberating free iodine from the iodide ; the absence of chlorine gas and nitrous acid, which would act in the same way, must be proved by using another test— -viz., red litmus and potassic iodide. The presence of either ozone or ammonia will cause the moistened litmus to turn blue, but red litmus' papers not saturated in the iodide would turn blue in ammonia ; therefore, if it be the cause of the change of color of the moistened litmus paper ita presence can be detected with the dry red litmus. The action of the iodide is shown by 2Kl+o=K 2 0 +I 2I 2 Hydrogen is obtained from water by passing a current of steam over heated iron, nickel, cobalt, or manganese in a state of fine division. Some metals, as gold and platinum, are not able to decompose water under any conditions ; sodium and potassium do so even when the water is cold, and the liberated hydrogen may be collected in any vessel inverted over the sodium on the water. It is a general law that when two elements combine heat is produced. Hydrogen may be collected from a Wolfe's bottle into a bell-jar by means of a siphon from the bottle, with the discharge-end turned upwards into the bell-jar through a sheet of paper pasted across the mouth of the bell. Should the hydrogen be exploded for the purpose of demonstrating its nature, the paper will give Way to the pressure and obviate any danger from breakage of the glass. After the lecture, Professor Black put the class through laboratory-practice in testing for silver, lead and mercury. With muriatic acid, each of these metals gives a white precipitate, which in the case of silver, ia dissolved by ammonia, of lead is unaltered, of. mercury is blackened. With bichromate of potash, silver turns dark red, lead turns yellow, and mercury gives an orange color ; with potassic iodide, silver gives a yellowish-white reaction, lead a yellow, and mercury a dirty green color.