Feb. lo, 1881] 



NA TURE 



341 



THE JOHN DUNCAN FUND 



MR. JOLLY informs us that the subscriptions sent to 

 form a fund to raise this old botanist above the 

 need of parochial relief and provide for his comfort during 

 his remaining years, has already reached a considerable 

 sum, all which has been sent spontaneously from all parts 

 of the country, without the formation of any conmiittee 

 or pressure whatever. More is coming in daily, and the 

 old man's future independence would seem in the end to 

 be pretty well assured. The sympathy shown in the case 

 has been widespread and of the warmest kind. Her 

 Majesty the Queen has graciously sent 10/., and the Duke 

 of Argyll, who sent 10/. at first, writes that it is a sub- 

 scription v.'hich ought to be zealously supported by all 

 who are interested in the pursuit of science, and who 

 honour the high moral and intellectual qualities by which 

 John Duncan is distinguished. All this speaks well for 

 the generosity of the country, but more is required. The 

 case is without doubt unusually deserving. 



The following is a list of the subscriptions which have 

 been received at this office during the past week : — 



£. s. ,f.\ 



£ 



EXPERIMENTS ON ICE, UNDER LOW 

 PRESSURES 



CERTAIN theoretical considerations on the relations 

 of the solid, liquid, and gaseous states of matter 

 led me three or four years ago to the speculation that in 

 a perfect vacuum the liquid state would be impossible, 

 and that under this condition it might be possible to raise 

 bodies to temperatures above their ordinary melting- 

 points. Tliese ideas were mentioned to one or two 

 friends at the time, but they naturally considered them 

 as speculations which would not be verified by e.\peri- 

 ment. From the pressure cf other work the subject was 

 for the time dropped, and it was not till the autumn of 

 1879 that an e.xperimental investigation was commenced. 

 The first substance tried was sulphur, but this was ulti- 

 mately found to be unsuitable, as under low pressures, 

 though it apparently Ijoiled as low as 130' C, yet at that 

 or a little above that temperature it began to froth. 

 Naphthalene was then tried, but as the pressure at which 

 the boiling-point fell below the melting-point was less 

 than about 7 mm., it was not easy to maintain the pres- 

 sure at a sufficiently low point. Mercuric chloride how- 

 ever, which was the ne.M body tried, yielded better 

 results. 



Mercuric chloride melts at 288°, resolidifies at 270°- 

 275", and boils at 303°. About 40 grammes of the pure 

 compound were placed in the tube a (Fig. i), and a ther- 

 mometer arranged with its bulb imbedded in the salt. 

 The drawn-out end of the tube was connected by stout 

 india-rubber tubing with one branch of the three-wayed 

 tube B, whilst the other was attached to the manometer c. 

 E was connected with a Sprengel pump fitted with an 



arrangement for regulating the pressure. When the pres- 

 sure had been reduced by means of the pump to below 420 

 mm., the mercuric chloride was strongly heated by the 

 flame of a Bunsen's burner, with the following results : — 

 Not the slightest fusion occurred, but the salt rapidly 

 sublimed into the cooler parts of the tube, whilst the 

 unvolatilised portion of the salt shrank away from the 

 side of the tube, and clung tenaciously in the form of a 

 solid mass to the bulb of the thermometer, which rose 

 considerably above 300° C, the mercury shooting up to 

 the top of the stem. After slight cooling, the air was let 

 in, and under the increased pressure thus produced the 

 saU attached to the bulb of the thermometer at once 

 melted and began to boil, cracking the tube at the same 

 time. 



The experiment was next varied as follows : —About the 

 same quantity of chloride was placed in the tube as before 

 and heated by the full flame of a Bunsen's burner. The 

 lamp was applied during the whole of this experiment, 

 and the size of the flame kept constant throughout. The 



mercuric chloride first liquefied and then boiled at 303° 

 under ordinary pressure, and whilst the salt was still 

 boiling the pressure was gradually reduced to 420 mm., 

 when the boiling-point slowly fell to 275°, at which point the 

 mercuric chloride suddenly began to solidify, and at 270° 

 was completely solid, the pressure then being 376 mm. 

 When solidification was complete the pump was stopped 

 working, but the heat still continued to the same extent 

 as before. The salt then rose rapidly to temperatures 

 above that at which a thermometer could be used, but not 

 the least sign of fusion was observed. From the comple- 

 tion of the'solidification to the end of the experiment the 

 pressure remained at about 350 mm. 



The above experiment, which was repeated three times, 

 shows therefore that when the pressure is gradually reduced 

 from the ordinary pressure of the atmosphere to 420 mm., 

 and the boiling-point simultaneously from 303° to 275°, the 

 salt solidifies while it is still boiling, notwithstanding that 

 it is being strongly heated at the same time, and that, 

 after solidification is complete at 270°, the temperaj.ure 

 then rises far above the ordinary boiling-point (303°) of 

 the substance without producing any signs of fusion 

 Under ordinary circumstances mercuric chloride melts at 



