1844.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



289 



tion, the bead of potassa formed runs over the water for a short time, but at 

 Inst is dissolved, evolving at the moment much steam . 



Lecture 4. May 11. 

 The effect of heat in causing (be passage of bodies through the states of 

 solid, liquid, and vapour, is exceedingly interesting, and in nothing more 

 beautiful than in water; it is interesting in water, not only on account of its 

 importance, but because it comes within the range of every one's observa- 

 tion. The change from the solid to the liquid state, and vice versa, is the 

 subject of the present lecture. The terms fusing, melting, or liquifying, are 

 indilTerently applied when a solid becomes a liquid ; and freezing, congealing, 

 crystallizing, or solidifying, expresses a liquid becoming solid. A piece of ice 

 when heated becomes water, and if the heat is contiu\ied the water will boil 

 and be converted into steam. Thus we have the same substance as solid, 

 liquid, and vapour, and by abstracting the heat it will return through the 

 same stages in the same order. These changes take |)lace with great regu- 

 larity ; there is a fixed point of heat at which they take place, and at no 

 other. Water can, by expedients, he reduced a few degrees below the usual 

 freezing temperature without becoming solid, but under ordinary circum- 

 stances it ceases to be liquid when it is lowered to the temperature marked 

 as .Ti" of Fahrenheit's thermometer. Solutions of several salts will serve to 

 illustrate this to an audience, perhaps better than water. Sulphate of soda 

 dissolved in hot water till the latter is saturated, may be cooled below its 

 crystallizing point if kept without agitation, but the moment it is touched, 

 crystals will shoot rapidly through the fluid till nearly the whole is solid. 

 The same can be effected with water, especially if the surface is covered 

 with oil. But though, when heat is abstracted, the strict changing point 

 may slightly vary, it is not so when heat is added ; ice cannot be made 

 warmer than 32 ' without becoming water, nor can water be heated above 

 212 without becoming steam. A list of the temperatures at which various 

 substances become solid, is here given ; — 



Congealing Points. 



Tallow 92° Fall. 



Spermaceti 112 



Yellow wax 142 



Sodium 194 



Tin 442 



Lead G12 



Zinc G80 



Sulpliuric ether -46° Fah 



Mercury —30 



Sulphuric acid + 1 



Vinegar 28 



Water 32 



Olive oil 36 



Acetic acid 50 



When heat is applied to ice, the temperature of which is 32°, it is seen to 

 melt, and if a thermometer he inserted into the mixture of ice and water, it 

 will be found to remain at 32 " so long as any ice remains undissolved. Now 

 how is it that the ice, which is continually absorbing the heat, does not form 

 water warmer tlian it was before the heat was applied. Ice, which has been 

 I gathering beat for several hours, has only been converted from ice-cold ice, 

 to ice-cold water. All the beat which has been received by it has been ab- 

 sorbed, is not sensible to the thermoraeier, and is called latent heat. Boiling 

 water may be poured upon ice, and yet, until all the ice is dissolved, the ther- 

 mometer will not indicate a greater heat than 32", or the freezing point. The 

 amount of beat thus rendered latent has been found to be 140"', which may 

 .be shown in the following manner. Take equal weights of water at :!3 ' and 

 ice at 32", and apply the same beat to both, and it will be found that the 

 heat required to raise the water 7", must he continued 21 times as long with 

 the ice to get the same temperature. Thus, 



Water at 33" took \ hour to gain 7°. 



Ice ,. lOj hours „ 



7° X 21 = 147° 



Deduct the 7° gained 7° 



140° 



It may he shown also to be this number by pouring equal weights of 

 water at 172° on ice at 32°, and the resulting water will be found 1o be at 

 32°, giving 140° absorbed. That solids when passing to the state of liquids 

 abstract heat, is readily proved by dissolving some sai-ammoniae in water. 

 At the tea table, the act of dissolving sugar in the cup cools the tea. On 

 this principle frigerific mixtures may be made, a few of which are here 

 given : — 



Mixtures. Parts. Thermometer Sinks. 

 Muriate of ammonia . . 51 



Nitre 5 V From 50° to 10° 



Water 16 J 



Nitrate of ammonia .. lip mo. .o 

 ,,, , , > rrom 50 to 4 



Water . . . . . . 1 J 



Sulphate of soda 

 Dilute sulphuric acid 



Snow 

 Common salt 



Muriate of lime 

 Snow 



1} 

 1} 



From 50° to 3° 



From 32° to 0° 



From 32° to -50° 



Owing to this property, water may be readily frozen by substances as 



warm as the room. \ common juggling amusement is to undertake to 

 freeze a saucepan to a stool before the fire. And it is to be done, by spilling 

 a little water on the stool, putting the saucepan in it, and then stirring in a 

 mixture of ice and snow. In a few minutes they are completely fixed 

 together, and the stool may be lifted by the saucepan. 



This latent heat, however, disappears only for a time, to re-ajipear when 

 wanted. For when liquids solidify they give up exactly the same amount of 

 beat that they bad before absorbed, which now becomes perceptible. Freez- 

 ing, therefore, is a warming process, because the water gives up the 140 de-. 

 grees of heat which it had rendered latent. An uncrystallized saturated so- 

 lution of sulphate of soda poured on the bulb of an air thermometer shows 

 an evident evolution of beat. These eft'ects are general, and in many in- 

 stances very curious, but sometimes it is increased or diminished by the in- 

 terference of chemical aftinity. The fluid alloy of potassium and sodium 

 when added to mercury, becomes fixed, a solid amalgam being left. Here 

 the eftect is increased by chemical aflinity. Occasionally chemical affinity 

 seems to contradict the general lav.s of solution ; for a solid, caustic potash, 

 when dissolving in water, evolves beat enough to fire phosphorus. In this 

 case there is cold produced by solution, but the heat caused by combination 

 is so great as to more than neutralize it. But sometimes these two effects 

 can be separated. Thus sulphuric acid and ice produce great heat when 

 mixed until the appetite of the acid for water is satisfied, but after that they 

 produce cold enough to freeze water. 



When water freezes, it expands considerably, 9 volumes becoming 10, and 

 is consequently lighter and floats on the surface, a small portion of the ice 

 remaining out of the water. It is this which accounts for the mountains of 

 ice which stand up in the sea, at the same time the size of these enormous 

 icebergs gives some idea of the immense quantity of ice which must be in the 

 water. 'I'his expansion takes place wilii great force. Experiments were 

 made on this point, by some officers in Quebec, by filling bomb shells with 

 water, and plugging them with iron, exposing them to the air to freeze. The 

 iron plugs were forcibly expelled, being shot to the distance of 50, 60, and 

 100 feet, the ice protruding from the holes. When the plugs were thoroughly 

 secured in their places, the bombs burst. Indeed, no mechanical force is 

 sufficient to control the chemical force of solidification. Small cast iron 

 bottles may he burst by filling them with water, and immetsing them in a 

 freezing mixture, bursting with a considerable report. Rocks are in this 

 manner split in nature, till crumbled down into a powder fit for agricultural 

 purposes. An old method, in the country, of freeing a kettle of the fur 

 which has accumulated, is to expose it wet to frost. The force of crystalli- 

 zation has been ingeniously proposed as a test of the strength and durability 

 of building stones. A piece of a certain size is dipped in a solution of a salt, 

 and hung up in the air ; crystallization takes place, which represents the 

 freezing of water, thus imitating the weathering of stones, and according to 

 the efi'ect so is it judged. 



The heat which is absorbed in summer by the melting of the snows and 

 glaciers is very great, as may be gathered by the torrents of water which flow 

 from them, and considering that evrry 3; cubic feet absorbs the heat given 

 off by a pound of coals. 



The facility with which ice adheres together is remarkable. If two pieces 

 rest together for a short time, they become frozen together. Ice adheres 

 also very strongly to flannel, hut not to linen, or to metal. No doubt this 

 power of adhesion of two surfaces of ice assists very much in the formation 

 of icebergs. 



In the next lecture the phenomena of vaporization of liquids, and liquefac- 

 tion of vapours, will be considered. 



OXFORD ARCHITECTURAL SOCIETY. 



The fifth annual meeting was held June 17, the Rev. the Rector of Exeter 

 College in the chair. 



After a few preliminary observations, the chairman read the annual report 

 of the committee. He congratulated the society on the steady progress of 

 the " Study of Gothic Architecture," which is daily becoming more general : 

 the good effects of this are already visible on all sides, and still greater eft'ects 

 may yet be looked for. He rejoiced to observe the formation and successful 

 progress of similar societies in various parts of the kingdom, and mentioned 

 particularly the Cambridge and the Exeter Societies as very flourishing and 

 eflicient. The mutilation and destruction of the remains of Gothic architec- 

 ture has been checked and well-nigh stopped, although a few more instances 

 may still be heard of occasionally, as at Newcastle, where an ancient chnrch 

 has been wantonly destroyed within the last few weeks ; the general indig- 

 nation with which such acts are now viewed, by all persons who have any 

 pretensions to the rank of educated or enlightened men, is a guarantee that 

 they will not be frequent. There is, however, another just ground of alarm 

 in the mischief which is daily peri)etrated under the name of restoration, 

 which, when conducted without sufficient knowledge, is often productive of 

 more injury than benefit, and should be very closely watched. Irreparable 

 injury is often done by ignorant persons, under the plausible pretext of 

 merely scraping oft' the whitewash, and still more when the decayed surface 

 of the stone has also to be scraped. 



In this university and city, there have been four instances of restoration 

 within the past year, which are deserving of praise. At St. John's College 



