EXPERIMENTS ON SPECIFIC HEAT. 821 



cooling through 1; and conversely, l kKr of mercury will 



take up - T th of a thermal unit if its temperature is 

 36 



raised through 1. Hence the specific heat of mercury, 



as given by this experiment, is or 0*028. 



oo 



The little flask containing the mercury should, for the sake of 

 safety, be heated in a ' sand bath.' It is placed upon a layer of dry 

 sand, or still better of dry iron filings, about l om high, contained in 

 an iron or tin saucer, which is supported over the spirit or gas 

 flame. 



With a wide centre-bit a hole is bored in a pretty 

 large block of ice, which must be as compact and free 

 from bubbles as can be obtained. The hole should be 

 just deep and wide enough to receive one of the leaden 

 weights of 98 gr , previously used in the experiments on 

 the laws of motion (see pages 48 and 55, and fig. 56). 

 A thin thread is tied to the weight, by means of which it 

 is held for some time immersed in boiling water; the 

 weight is then quickly taken out of the water and placed 

 in the hole in the ice, which, just previous to putting 

 the lead into it, must be carefully wiped smooth inside 

 with a rag, so as to remove any small loose bits of ice 

 left in the hole; water which may have collected in the 

 hole should be sucked up with a pipette or a suitably 

 prepared pointed tube. After the lead has been left 

 for a few minutes in the ice, and has given up its 

 heat to it, it is taken out again, and the water 

 now left in the hole is carefully sucked up with a 

 pipette and dropped into the smaller graduated tube, 

 fig. 39, page 38. Its bulk will be about 3 CC *75. The 

 hole in the ice is now enlarged by scraping with a knife 

 until it is about 6 cm wide and deep, and, after carefully 



