PHYSICAL PROPERTIES OF WATER, ETC. ..7 



with the gun at the temperature of the air,— it would lie almost impossible to keep it 

 steadily at a much lower temperature,— so that I had to work in water at about 12° C. 



" The process employed was very simple. A tall cylindrical jar full of water had 

 two Challenger thermometers (stripped of their vulcanite mounting) at the bottom, and 

 was more than half-filled with fragments of table-ice floating on the water, and confined 

 by wire-gauze at the top. This was lowered into the water of the gun, and pressure 

 was applied. 



" It is evident that if there were no conduction of heat through the walls of the 

 cylinder, and if the ice lasted long enough under the steadily maintained pressure, the 

 thermometers would ultimately show, by their recording minimum indices, the maximum- 

 density point corresponding to the pressure employed : — always provided that that 

 temperature is not lower than the melting point of ice at the given pressure. 



" Unfortunately, all the more suitable bad conductors of heat are either bodies like 

 wood (which is crushed out of shape at once under the pressures employed) or like 

 tallow, &c. (which become notably raised in temperature by compression). I was 

 therefore obliged to use glass. The experiments were made on successive days, three 

 each day, with three different cylindrical jars. These had all the same height and the 

 same internal diameter. The first was of tinned iron ; the second of glass about £ inch 

 thick ; the third, of glass nearly an inch thick, was procured specially for this work. 



" With the external temperature 12° - 2 C, the following were the results of 1^ tons 

 pressure per square inch, continued in each case for 20 minutes (some unmelted ice 

 remaining on each occasion). The indications are those of two different Challenger ther- 

 mometers, corrected for index-error by direct comparison with a Kew standard : — 



The coincidence of the first numbers with the ordinary maximum-density point of water 

 is, of course, mere chance. When no pressure was applied, but everything else was the 

 same, the result was — 



Tin. Thin. Thick. 



5°-7 C 5° 4° 



It is clear that the former set of numbers points to a temperature of maximum density, 

 somewhere about 0° C, under 1^ tons pressure per square inch. But still the mode of 

 working is very imperfect. 



" I then thought of trying a double cylindrical jar, the thin one above mentioned 

 being enclosed in a larger one which surrounded it all round, and below, at the distance 

 of about f inch. Both vessels were filled with water, with broken ice floating on it, 



(rHYS. CHEM. CHALL. EXP. rAET IV. — 1888.) 8 



