302 Professor Dewar on the 



Furnace. The following extract from the lecture will explain 

 how the subject was introduced. : — 



" Meteorites, no doubt, have an exceedingly low tempera- 

 ture before they enter the earth's atmosphere, and the ques- 

 tion had been raised as to what chemical reactions could take 

 place under such conditions. It resulted from Professor 

 Dewar's investigations that at a temperature of about 

 — 130° C. liquid oxygen had no chemical action upon 

 hydrogen, potassium, sodium, phosphorus, hydriodic acid, 

 or sulphydric acid. It would appear, therefore, that as the 

 absolute zero is approached even the strongest chemical 

 affinities are inactive. 



" The lecturer exhibited at work the apparatus by which he 

 had recently succeeded in solidifying oxygen*. The apparatus 

 is illustrated in the accompanying diagram [p. 301], where a 

 copper tube is seen passing through a vessel kept constantly 

 fall of ether and solid carbonic acid ; ethylene is sent through 

 this tube, and is liquefied by the intense cold ; it is then con- 

 veyed by the tube, through an india rubber stopper, into the 

 lower vessel ; the outer one is filled with ether and solid 

 carbonic acid. A continuous copper tube about 45 feet long, 

 conveying oxygen, passes through the outer vessel, and then 

 through that containing the liquid ethylene ; the latter 

 evaporates through the space between the two vessels, and 

 thus intense cold is produced, whereby oxygen is liquefied in 

 the tube to the extent occasionally of 22 cubic centimetres at 

 one time. The temperature at which this is effected is about 

 — 130° C, at a pressure of 75 atmospheres, but less pressure 

 will suffice. When the oxygen is known to be liquid, by 

 means of a gauge near the oxygen inlet, the valve A is 

 opened, and the liquid oxygen rushes into a vacuum in the 

 central glass tube below ; some liquid ethylene at the bottom 

 of the next tube, outwards, is also caused to evaporate into a 

 vacuum at the same moment, and instantly some of the liquid 

 oxygen in the central tube becomes solid, owing to the intense 

 cold of the double evaporation. The outer glass vessel serves 

 to keep moisture from settling on the sides of the ethylene 

 tube. By means of the electric lantern and a lens, an image 

 of this part of the apparatus was projected upon the screen, 

 this being the first time that the experiment had been shown 

 on a large scale in public. 



" Performing this experiment the temperature reached was 

 a little below 200° C, that is only 50° or 70° above the 



* The white material taken for solid oxygen in 1836 was due to gaseous 

 impurity. 



