1879.] HEATING BY HOT WATER. 377 



conjured up is only a bogus ghost at the test, which I am sure will not trouble 

 us much. 



It only further remains for me to notice Mr Hammond's extraordinary experi- 

 ment to prove that practically water is an absolute non-conductor. In any case, 

 whatever it proves, it does not prove that water is practically a non-conductor. I 

 think, if I recollect right, I have seen something about such an experiment to 

 illustrate the doctrine of what is called the latent heat of liquefaction and the 

 specific heat of water. Had Mr Hammond informed himself properly he would 

 have known that the reason why his hand in his experiment will not feel any 

 sensation of heat until the whole of the ice is melted, is not because it is an 

 absolute non-conductor, but because of the great amount of latent heat taken up 

 in the passage of water from the solid to the liquid state ; for it is found that it 

 takes as much heat to rnelt one pound of ice at 0° as to raise one pound of water 

 from 0° to 79.24° ; therefore the latent heat of fusion of water is fixed at 79.24° 

 centigrade, or 142.65° Fahr. — (See Deschand's Natural Philosophy, trans- 

 lated by Professor Everett, part ii., pp. 426-444.) In other words, one pound 

 of ice at 32° Fahr. requires as much heat to melt it, without raising the tem- 

 perature one iota, as will suffice to raise one pound of water from 32° to 142.65° 

 Fahr. But the conducting power of water need not be a disputed powej at 

 all : it has been fixed just as definitely as the conducting power of solids ; and 

 although a very feeble conductor compared to most of the metals, such as gold, 

 silver, copper, &c, makes a favourable comparison with the earths. 



As I said before, liquids are bad conductors, but water is one of the best. From 

 experiments made by Despretz, he fixed the conducting powers of various sub- 

 stances as follows : Gold, 1000 ; silver, 981 ; copper, 897 ; zinc, 363 ; lead, 

 179; porcelain, 12; iron, 374; tin, 304 ; marble, 23 ; brick-earth, 11. He fixes 

 the conducting power of water at y \, that of copper-ore 9.44, while copper is 8.97 ; 

 therefore any one will see that although it is not a good conductor compared to 

 some solids, it is about as good as some others, — which shows that Mr H.'s rough- 

 and-ready way of deciding the point is worth nothing ; but if he will take a rough- 

 and-ready method, let him go to a Turkish bath at a temperature of 160° ; he 

 will find he can bear it easily, if not comfortably, — he can handle wood, cloth, &c. , 

 without inconvenience. But let him put his hand into water at 160°, and I 

 rather think he will come to the conclusion that it is not a non-conductor, for it will 

 part with its heat into his hand in a manner more sudden than agreeable. Or, 

 on a frosty morning, with the temperature at zero, let him handle wood, stone, 

 cloth, and ice in the open air, when they must, of course, be all at the same tem- 

 perature. He will find that the ice will conduct the heat from his hand suffi- 

 ciently quick to make it very unpleasant, and very much quicker than wood, 

 cloth, and many other substances. In fact, as I said already, it is exceedingly 

 inconvenient in discussing any question to have to prove every fundamental 

 point which ought to be known to every schoolboy. In conclusion, I have only 

 to state that, if the explanations already given do not convince Mr Hammond 

 that he is wrong fundamentally on almost every point, I despair of making it 

 plainer. A. D. Makenzie. 



2 Grove Terrace, Edinburgh. 



I have already encroached too much on your valuable space in reply to Mr 

 Hammond, that I cannot ask you to find room but for a few words in reply to 

 J. S. W., who asks my opinion about the failure of the miniature hot-water 

 apparatus described by him. While not professing to dogmatise in such matters* 

 I am of opinion that the cause of the failure was the enormous amount of 



