^70 



SCIENCE. 



liquids by 

 their own 

 pressure. 



Science, much lower than water or any known fluid, and that 



Curiosities o f the other fluid CD is a little less than water. Small 



' n * spicular crystals are sometimes found in these cavities, 



S -T""~ / See the Edinburgh Transactions, Vol. X. p. 1. and Dr. 



Brewster's Journal of Science, Vol. IV. 



13. On the Condensation of Gases into liquids by their 

 own pressure. 



On the con- The condensation of gases into liquids discovered by 

 densation of Mr. Faraday, is one of the most curious experiments in 

 gases into modern chemistry. The gas with which the experi- 

 ment may be most easily and safely made, is Cyano- 

 gen. For this purpose take some pure cyanuret of 

 mercury, made perfectly dry by heating, and having 

 put it into one branch of a glass tube bent like the let- 

 ter A, the branches being about two inches long, seal 

 the other end of the tube hermetically. If the heat of 

 a spirit lamp is applied to the end of the tube contain- 

 ing the cyanuret, while the other is kept cold, the cy- 

 anogen gas will be produced by the decomposition of the 

 cyanuret and passing over into the cool end of the tube 

 will be condensed by its own pressure or expansive 

 power into a pure and colourless fluid, having a refrac- 

 tive power rather less than water. The pressure of the 

 vapour of cyanogen appeared to be a little more than 

 three and a half atmospheres at 45 of Fahrenheit. 



By a process similar to the -preceding, Mr. Faraday 

 succeeded in liquefying sulphurous acid gas, sulphuretted 

 hydrogen, carbonic acid, euchlorine, nitrous oxide, ammo- 

 nia, muriatic acid, and chlorine. See Philosophical 

 Transactions, 1823, p. 189- 



Sir Humphry Davy has also used a very simple me- 

 thod of liquefying the gases by means of heat. He 

 places the gas in one leg of a bent tube confined by 

 mercury, and applies heat to ether, alcohol, or water 

 put in the other end of the tube. By the pressure of 

 the vapour of these fluids he liquefied Prussicacid gas 

 and sulphurous acid gas. See Philosophical Transac- 

 tions, 1823, p. 199. 



14-. Remarkable experiment on the expansion of ether. 



Take a tube of glass about two inches long and 

 ble experi- three-tenths of an inch in diameter, and fill it about 

 ment on the three-fifths full of ether. Fix the tube by means of a 

 expansioncf w j re to a piece of stick about two feet long, and hold 

 the ball either over a spirit lamp or within the bars of 

 a good fire, turning it round so as to receive the heat 

 equally. The ether will be seen to expand, and when 

 the heat is about 300, the ring of fluid which adheres 

 to the glass by capillary attraction, becomes smaller 

 and smaller and the fluid more and more voluble, till 

 it at last fills the whole tube, the ether having expand- 

 ed two-fifths of its original bulk. When the tube is 

 allowed to cool in a vertical position various currents 

 ascending and descending appear, and then a cloud 

 suddenly shows itself at within less than two-fifths of 

 the tube from its top, accompanied by a rapid ebulli- 

 tion, which announces the conversion of the vapour 

 which filled the tube into liquid. 



This experiment is exceedingly curious, and we 

 .have performed it repeatedly and shown it to others 

 with no other precaution than holding the tube behind 

 a thick plate of mica in case of its bursting. 



The same results take place whether atmospheric 

 -air occupies the two- fifths of the tube that is left empty, 

 or whether the air is driven off by the ebullition of the 

 .ether. 



The part of this experiment respecting the expansion 



of the ether so as to fill the tube is due to Baron Cag- 

 nard de la Tour. 



Science. 



Curiosities 



Rtmark- 



ether. 



15. Protection of t/ie copper of ships and of culinary v-^y^o^ 



utensils by rendering it negatively electrical. 

 Sir Humphry Davy had long ago shown, that the Trotection 

 chemical action of bodies upon each other may be mo- of the cop- 

 dified or destroyed by changes in their electrical states ; V et of S "'P S 

 that substances will combine only when they are in" an t g" s ;j" s 

 different electrical states; and that by bringing a body byrendering 

 naturally positive, artificially into a negative electrical it negatively 

 state, its usual powers of combination are altogether electrical, 

 destroyed. By reasoning upon this general principle, 

 which had previously conducted him to many brilliant 

 discoveries, Sir Humphry was led to the discovery 

 which we propose at present to explain. Copper being 

 a metal only weakly positive in the electro-chemical 

 scale, he conceived that if it could only act on sea wa- 

 ter in a positive state, and consequently that if it could 

 be rendered slightly negative, the corroding action of 

 sea water upon it would be destroyed. After many 

 trials, he obtained the most satisfactory confirmation of 

 these theoretical views. A piece of zinc as large as a 

 pea, or. the point of a small iron nail, preserved 40 or 

 50 square inches of copper from corrosion, whether it 

 was placed at the top, bottom, or on the middle of the 

 sheet of copper, and whatever was the shape of the 

 copper. Every side, every surface, and every particle 

 of the copper continued bright, while the zinc or the 

 iron was slowly corroded. 



A piece of thick sheet copper, containing about 60 

 square inches of surface, was cut, so as to form seven 

 divisions, connected only by the smallest filaments, and 

 a mass of zinc, of the fifth of an inch in diameter, was 

 soldered to the upper division. The whole was plunged 

 under sea water, and after the lapse of a month the 

 copper was as bright as when first introduced, while 

 similar pieces of copper undefended had undergone 

 considerable corrosion. 



The application of these results to the preservation 

 of the copper sheeting of ships of war and other vessels 

 is obvious. Under the sanction of the Lords Commis- 

 sioners of the Admiralty, Sir Humphry has been en- 

 gaged in ascertaining the value of this discovery upon 

 ships of war, and we learn with the happiest effect. 



The Samarang, which had been coppered in India, in 

 1821, came into dock in the spring of J824, covered 

 with rust, weeds, and zoophytes. She afterwards set 

 out for Nova Scotia, protected with four masses of iron, 

 equal in surface to about one-eightieth of the copper, 

 two being placed near the stern, and two on the bows. 

 She returned in January 1825, remarkably clean, and 

 in good condition. 



All vessels of copper, used in cookery may likewise 

 be protected from oxidation, by a piece of tin or iron. 

 See the Phil. Transactions, 1824, p. 151 ; and Dr. 

 Brewster's Journal of Science, vol. I. 



16. On the singular effects of intoxicating gas. 



The intoxicating gas, otherwise called the nitrous o n the bin- 

 oxide, or the gaseous oxide of azote, is, like atmos- gular effects 

 pheric air, a compound of oxygen and nitrogen gas, and of intoxicat- 

 diflfers from it only in having a greater quantity of oxy- in S S as> 

 gen, and from being composed of -27 parts of oxygen 

 and 73 of nitrogen, while the nitrous oxide is com- 

 posed of 37 parts of oxygen and 67 of nitrogen. 



In order to procure the nitrous oxide, nitrate of 

 ammonia is put into a tubulated glass retort, and ex- 



