1894.] 



KNOWLEDGE 



151 



by a steel piston working in a cylinder, the hydraulic 

 cylinder being tilled with water. The gas was contained 

 in a capillary glass tube with small bore and thick walls 

 which could support the strong pressure required. The glass 

 tube containing the gas was connected to the hydraulic 

 pump by means of a flexible metallic tube. Cailletet 

 worked with small quantities of gas, while Pictet, by 

 means of his machinery, was able to obtain relatively large 

 quantities of the various liquefied gases. 



The results got were only obtained after years of 

 preparation and endeavour by both experimenters, 

 working quite separately and independently. Cailletet 

 made use of the skill and knowledge obtained by him in 

 the prosecution of his business of an ironmaster at his 

 works at Chatillon-sur-Seine ; while Raoul Pictet carried 

 on his experiments at Geneva, where he was engaged as 

 a manufacturer of ice-making machinery. 



Cailletet's apparatus is singularly simple and effective, 

 and by it he also obtained liquid hydrogen, which appeared 

 as a mist on the inside of his tube when the great pres- 

 sure to which the gas was subjected was suddenly relieved, 

 and heat thus suddenly absorbed. Hydrogen was thus 

 liquefied into globules of mist on the glass when the pres- 

 sure of three hundred atmospheres was suddenly removed, 

 while air previously carefully dried changed into a liquid 

 under a pressure two hundi-ed times that of the atmosphere 

 after it was cooled by means of liquid nitrous oxide. This 

 is what happens in Cailletet's experiment : the gas, first of 

 all cooled on account of its quick expansion, descends m 

 temperature below its critical point, and then becomes 

 liquid under the moderate pressure to which it is then 

 ex250sed. But as expansion and relief of pressure con- 

 tinues, the liquid is soon under too little pressure to remain 

 in this condition, and besides by conduction from surround- 

 ing objects heating occurs, so that the liquefied gas soon 

 evaporates and the mist produced is fugitive ; this is 

 especially so in the case of hydrogen. 



MM. Wroblewski and Olzewski have carried out many 

 experiments, using an apparatus similar to Cailletet's. At 

 — 136° Cent, a pressure of twenty atmospheres sufficed to 

 liquefy oxygen, and the critical temperature of this gas is 

 placed at —112° Cent., that is, it must be cooled at least as 

 far as this before liquefaction can take place. The critical 

 temperature of nitrogen is found to be still lower than this, 

 being - 147° Cent., or - 223°Fahr. 



On Friday evening, .June 2Gth, 1891, at the Pioyal Insti- 

 tution, the audience saw liquid oxygen in large quantities 

 freely drawn off' from the refrigerating apparatus, and 

 having all the appearance of hot water, with a vaporous 

 cloud above it. In reality the oxygen was boiling at a 

 temperature of - 290° Fahr. — i.e., 328° below freezing 

 point, and the apparent vapour consisted of ice particles 

 produced from the moisture of the surrounding air, cooled 

 from the contact of the chilled gas. On filtering the liquid 

 oxygen, to get rid of the minute particles of solid carbonic 

 acid scattered through it, it was seen to consist of a blue 

 limpid liquid not unlike water. It would naturally be expected 

 that the liquefied gas, when placed in an open vessel in a 

 room at the ordinary pressure and temperature, would with 

 great rapidity, and even violence, hasten to take the gaseous 

 form. But this was not the case ; the liquid oxygen evaporated 

 but slowly, and retained its liquid form for a considerable 

 time, although it was only under the usual atmospheric pres- 

 sure. When a few drops of the liquid were thrown into 

 water, the eft'ect was like that of plunging red-hot iron into a 

 liquid ; a fizzling noise was produced, and soon the globules 

 of liquid oxygen were seen each floating about in a little 

 cup of ice formed from the surrounding water. By means 

 of the remarkably cold fluid, alcohol, which remains liquid 



in even the severest Arctic climate, was quickly frozen into 

 solid lumps ; the solidifying temperature for alcohol being 

 -130° Cent. 



The efi'ect of cold in rendering sluggish and inert sub- 

 stances which are usually chemically active is strikingly 

 seen in the case of cooled oxygen. At ordinary 

 temperatures oxygen gas has a great affinity for phos- 

 phorus, and combines readily with it, producing vigorous 

 combustion with much heat, and light clouds of the solid 

 phosphorus oxide being formed. But a piece of phosphorus 

 when placed in liquid oxygen remains undisturbed ; no 

 combination takes place. 



By means of liquid oxygen, nitrogen may be liquefied. 

 Advantage is taken of the fact that liquid oxygen, when 

 placed in vacuo, boils at a lower temperature than when 

 under the ordinary pressure. A temperature of 328° Fahr. 

 can thus be obtained, at which both nitrogen and atmos- 

 pheric air can be liquefied. During the process of 

 liquefaction of air, the two gases of which it is made up 

 become liquid together, but when the temperature is 

 allowed to rise they evaporate separately. The nitrogen, 

 though more difficult to liquefy, comes off as a gas first, 

 leaving almost pure oxygen behind. 



Prof. Dewar has also solidified air as well as nitrogen by 

 employing powerful pneumatic apparatus. Pure oxygen has 

 itself never been obtained in the solid form. In order to obtain 

 a succession of lower and lower temperatures, the various 

 liquefied gases are caused to boil in a vacuum. Thus, the 

 more easily liquefiable gases are made use of to abstract 

 heat on their evaporation from those more difficult to 

 liquefy. When these latter are made to boil in vacuo a 

 still lower temperature is attained, and by successive steps 

 a reading on the thermometer as low as — 211° Cent, (or 

 — 346° Fahr.) has been reached. At these low temperatures 

 experiments of an interesting character have been made on 

 the electrical behaviour of metals, and their electrical 

 resistance has been determined. 



On boiling successively in vacuo carbonic acid, nitrous 

 oxide, and ethylene, using the first to take away by their 

 evaporation heat from the gases which are more difficult to 

 Uquefy, a temperature of — 229° Fahr. is reached, at which 

 oxygen can be liquefied under a pressure of fifteen hundred 

 pounds per square inch. The rapid evaporation of oxygen in 

 vacuo so quickly removes heat from surrounding sub- 

 stances that air and nitrogen are soon liquefied, and these, 

 when treated under powerful air pumps, abstract sufficient 

 heat to allow of the production of solid nitrogen. This last 

 experiment was successfully carried out for the first time 

 in public on January 19th, 1894. 



THE MAN-LIKE APES. 



By E. Lydekkek, B.A.Cantab., F.E.S. 



THROUGH the generosity of the Board of Governors 

 of the Cheltenham Hospital, the Natural History 

 Branch of the British Museum has been recently 

 enriched by a specimen of great historical interest 

 in the shape of the skeleton of a young chimpanzee 

 from Angola, which was dissected and minutely described 

 so far back as 1699, by Dr. Edward Tyson, in a rare work 

 entitled " Orang-Outang, sii-e Homo Sylvestris," a copy of 

 the volume being appropriately placed alongside of the 

 skeleton in one of the bays on the left side of the great 

 entrance hall. The work in question is the first account 

 of a member of the group of man-like apes having any 

 pretension to scientific accuracy ; and the acquisition by 

 the Museum of the skeleton and the volume in which it is 

 described may well serve as the text for a short account of 

 the man-like apes in general. 



