318 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[Au GUST, 



'' The want of adequate plans of districts, and the necessity for a general 

 survey with the levels properly laid down, and level marks placed in pro- 

 perty localities seems to he well estahlished. In most eases, the memory or 

 memoranda of the surveyors constitute the most available record. 



The want of power on the part of commissions to construct new sewers 

 under the present acts was commented on as a serious evil, to which no doubt 

 a remedy will be applied. 



PROFESSOR FARADAY ON HEAT. 



A course of eiyhi Lectures delivejcd at the Royal Institute, 



Lecture V., May 18, 1844. 



(Specially reported for this Journal.) 



Amongst the phenomena accompanying the change of matter from the 

 solid or fluid to the vaporous state, the vast increase in bulk is perhaps the 

 most striking. If a small piece of camphor is placed in a flask and heat ap- 

 plied, it will be found that in a short time the whole of the flask will be filled 

 with its vapour, which may be lighted at the mouth of the flask. When 

 cooled it returns to its former solid state, and thus illustrates the difference 

 between vapours and gases, the latter being permanent at ordinary tempera- 

 tures, whilst the former require a higher heat to maintain them in the gaseous 

 state. It is therefore seen tliat heat does not produce any permanent change 

 in these cases, that, in fact, the change is only mechanical and temporary. 

 The phenomena of ebullition may be accurately watched by using a transpa- 

 rent boiler, such as a glass tube, or still. Volumes of steam are formed which 

 in the still condense into a few drop<i of water, which drops may be taken as 

 a measure of the quantity of steam formed, for it is known that water is in- 

 creased in bulk 1700 times by being converted into steam. 



When water is heated, it increases in heat until it arrives at the boiling 

 point or 212°, and though the heat may be continued for any length of time, 

 the water becomes no hotter, but continues to give off steam of the same 

 temperature as itself. There is here, then, the same phenomenon as when 

 heat is applied to ice, and it is owing to the same cause, viz.. the absorption 

 of latent heat by the steam, though to a much greater extent than in the 

 case of water. Indeed, almost all the heat which is added to boiling water 

 is rendered latent. This heat, however, may he all rendered sensible by con- 

 densing the steam, and in this manner cold water may be boiled by passing 

 steam into it at a distance from the source of heat. One pound of steam 

 will heat 6 or 7 pounds of water to the boiling point. In experiments car- 

 ried on to ascertain the quantity of heat rendered latent by steam, it was 

 found that lib. of steam passed into 101b. of water at 60°, left Ulb. of water 

 at 160°. The matter therefore stood thus : — 



10 lb. of water had gained 100° each = 1100" 

 1 lb. of steam at 212" had lost . . . 52° 



Therefore the latent heat of steam is 948° 

 The same amount of heat is found to be abstracted when steam is formed. 

 There are many processes in the arts where it is not convenient to apply heat 

 directly to a vessel, and in these cases steam is frequently used. Brewers, 

 for instance, heat their liquors in this manner. 



Water in being converted into vapour increases in bulk more than any 

 other liquid, thus — 



1 volume of Water becomes 1696 volumes of vapour. 

 1 „ Alcohol „ 659 „ 



1 „ Ether „ 443 



It thus becomes specifically lighter than the air, and is therefore enabled 

 to rise through it ; for it is found that. 



The specific gravity of steam is 0-625 

 „ „ air 1-000 



„ vapour of alcohol 1-613 



„ „ ether 2.580 



By this means the vapour of water is carried into the upper and colder re- 

 gions of the air, and there being condensed, falls on the high lands, and 

 flow agains to the valleys as rivers. The vapour of camphor is too heavy to 

 rise in the air, and may be poured from one vessel into another like water. 



The boiling point of water, though at the surface of the earth, it is always 

 about 212°, depends entirely on the pressure of the atmosphere. Thus wa- 

 ter can be made to boil at exceedingly low temperatures, by removing the 

 pressure of the air. Water which feels but slightly warm to the hand, boils 

 under the receiver of an air pump. Alcohol will boil when cold, under the 

 same circumstances. If a retort he filled with boiling water, and the neck 

 corked up and put into cold water, the water will continue to boil for an 

 hour or more. Water can also be made hotter than 212°, by increasing the 

 pressure ; for instance, by heating it in a closed vessel, when the pressure of 

 its own vapour prevents it from boiling, and the temperature rises in propor- 

 tion. The rate at which the beat increases with the pressure is shown in the 

 following table. 



Atmospheres. Degrees. Atmospheres. Degrees. 



At a pressure=l the heat is 212 At a pressure = 8 the heat is 342 



k curious fact has been remarked with respect to the boiling point, that is, 

 that it is sHghtly affected by the nature of the vessel containing the water. 

 In two vessels, one of copper, the other of perfectly clean glass, the water 

 in the copper will boil at 3" lower temperature than that in the glass. The 

 bubbles which are given off in boiling, though in general rising form the bot- 

 tom of the liquid, may, owing to this property, be made to rise form any 

 part by inserting a bunch of metal wire in it. A piece of wood will In the 

 same manner, regulate the bubbling spot in alcohol. Copper filings dropped 

 into water, lowers the temperature of boiling, changes the place of boiling 

 and breaks up the large bubbles into small ones. This difference of boihng 

 point according to the containing vessel, must be taken into consideration 

 in graduating thermometers, or great errors will be introduced into the 

 graduations. 



A list is here given of some fluids which readily pass from the liquid to the 

 vaporous state, with the pressures and temperatures requisite to efli'ect the 

 change ; the first column of figures expresses their boiling points at common 

 pressure, the second, the pressure requisite at 60° to convert their vapours 

 into liquids : — 



Nitric oxide 



Carbonic acid 



Hydrochloric acid 



Ilydrosulphuric acid 



Ammonia 



Cyanogen 



Chlorine 



Sulphurous acid 



Sulphuric ether 



Sulpliuret of carbon 



Alcohol 



Water 



Spirits of turpentine 



Sulphur 



Oil of vitriol 



Mercury 



The effects which take place when bodies pass from the solid or liquid to 

 vapour, are somewhat similar in all cases. Nearly all bodies evaporate below 

 their boiling point. A little ether poured into a spouted vessel, fills the 

 whole of it with its vapour, which may b? poured out or lighted at the spout. 

 In like manner water is continually evaporating at all temperatures, and dur- 

 ing evaporation producing the sensation of cold, owing to the heat which it 

 renders latent. It is on this principle that wine coolers act. Dr. Wollaston's 

 cryophorus, freezes water by its own evaporation. It consists of a glass tube 

 with a bulb at each end, sealed hermetically and containing a little water 

 without air. The water being at one end, the other end is immersed in some 

 ice, which, condensing the vapour as quickly as it is formed, so reduces the 

 temperature that the water at the other end becomes frozen. Amusing in- 

 stances of this ready evaporation of water occurs occasionally in domestic 

 economy, when buns and biscuits are shut up in one case together. The water 

 evaporates from buns and is readily absorbed by the dry biscuit, and becomes 

 hard and sandy, whilst the biscuit which should be crisp becomes moist. 



The physical history of vapour and the uses to which they are applied, has 

 recently acquired great importance. The mechanical action of the vapour of 

 water in the steam-engine is known to be almost without limits. This 

 power arises from the vapour of water requiring 1700 times its original space, 

 and the pressure which it exerts to fill that space. If an orifice be left in the 

 vessel in which the steam is generated, sufliciently large, no effect will be 

 there produced ; hut if not, and heat is continued, the vessel will yield to the 

 great pressure, and explosion will result. This may be illustrated by a little 

 toy known as the candle cracker, which is a drop of glass with water in the 

 interior ; this placed in the tallow of a candle becomes heated, steam is gene- 

 rated, and at last explodes with noise, and extinguishes the candle. This ex- 

 hibits the force of expanding steam as well as on a larger scale. If a glass 

 tube be blown into a bidb in the middle, and turned upwards with a very 

 fine opening at one end, on heating the bulb enclosing the larger end, the 

 vapour of ether will drive the liquid with great force into the air, which if 

 lighted, will form a splendid stream of fire. The tendency of the pressure of 

 the air to crush steam boilers which have been filled with steam, and which 

 has subsequently been condensed, is shown strikingly by boihng a little 

 water in a tin canister, closing it tightly when full of steam, then allowing 

 it to cool, or more quickly by pouring water on it ; the whole vessel will be 

 collapsed and doubled up. 



Lecture VI.— Mat 25, 1844. 



When water and oil, of the same temperature, are brought into a warm 

 room, they will be found, in time, to acquire the temperature of the room, 

 but the oil will arrive at its full heat in half the time required by the water. 

 From this it is inferred that bodies absorb various quantities of heat to arrive 

 at the same temperature ; and this is fully borne out by further investigation. 

 This, which is called their capacities for heat, is found to vary with every 

 substance, each substance rising in temperature by the application of the 

 same amount of heat, according to its own rate ; that body which requires the 

 most heat to raise its temperature a certain degree, being said to have the 



