66 



NATURE 



[November 15, 1894 



the gas the air was expelled by the exit-tube, and the gas which 

 condensed in the upper portion of the cylinder collected in the 

 lower portion. When the protecting mantle was removed the 

 relatively warm air soon promoted ebullition, and the escaping 

 vapour was as rapidly recondensed in the cooled upper portion 

 of the cylinder, and fell back into the lower. If the hand were 

 brought into the proximity of the cylinder, the boiling became 

 most vigorou-. At first propane usually boils irregularly, 

 .quiescent intervals being s^ucceeded by almost explosive ebulli- 

 tion ; bat after a short time the formation of vapour becomes 

 perfectly regular, and a mercury thermometer dipping in the 

 liquid registers a temperature of - 3S°. After comparison of 

 the latter with an air ihermouieler, the correct temperature of 

 the boiling-point of propane is found to be - 37" at 760 m.m. 

 pressure. 



Propane may safely be sealed in strong glass tubes after con- 

 densation by means of solid carbon dioxide, and thus preserved 

 in the liquid state. It is a perfectly colourless liquid, Imt much 

 more viscous than liquid carbon dioxide. The critical tem- 

 perature was determined by use of such a tube half filled with 

 the liquid. The tube was immersed alongside a thermometer 

 in a bath of liquid paraffin, furnished with a suitable stirrer. 

 Upon heating the apparatus to 101° the liquid meniscus com- 

 menced to become hazy, and the distinction between gas and 

 liquid became less and less pronounced until at 1 10° all trace of 

 it had disappeared. Upon cooling, the well-known nebulosity 

 was observed at 102°, and this temperature is considered to be 

 a close approximation to the critical temperature of propane. 



The vapour pressures of propane for different temperatures up 

 to I2^'5 were determined by enclosing a quantity of the 

 liquefied hydrocarbon in one limb of a U-tube and dried air in 

 the other limb, the two being separated by means of a short 

 column of mercury. The closed apparatus was then cooled to 

 various temperatures in suitable baths, and the vapour pressures 

 calculated from the amount of compression of the air column. 

 The vapour pressures for temperatures superior to the ordinary 

 were determined by use of the Cailletet appar.itus and spring 

 manometer. The following table represents a summary of the 

 results : 



The critical pressure of propane corresponding to the critical 

 temperature of 102° is consequently 485 atmospheres. 



Dr. Plainlcn has also determined the density of liquid pro- 

 pane at several temperatures. It is 0'536 at 0°, 0524 at 6°'2, 

 0*520 at if'S, and o'5lS at I5°'9, compared with water at 4°. 



An investigation of the properties of liquid ethane upon 

 similar lines naturally presented greater difficulties, on .account 

 of the further removal of its boiling-point from the ordinary 

 temperature. The j^ure gas cannot be so conveniently prepared 

 by the method of Kohnlein, as the sealed tubes frequently ex- 

 plode with great force. It was therefore obtained by the well- 

 known method of Gladstone and Tribe from ethyl iodide and 

 the zinc-copper couple. A mixture of ether and solid carbon 

 dioxide is insufficient to effect liquefaction of the gas, but liquid 

 ethylene was found to bring about the necessary reduction ol 

 temperature, which latter was mcasiircrl by means of a copper- 

 silver thermoelement. Liquid ethane in the pure state is 

 perfectly colourless. 



The boiling-point of ethane was determined as in the cose of 

 propane, the upper part of the apparatus, however, being sur- 

 rounded by the liquid ethylene instead of solid carbon dioxide. 

 Thecthylcnc was j»rcvented frotii vapr>urising rapidly by allowing 

 the cxIreDicly cold vapour proiluced by the evaporation to pass 

 through an outer cylinder, and thus to act as a protective cold 

 bath. The ethane was first cooled by means of ether and solid 

 carbon dioxide before admission into the boiling-point 

 apparalun, after which it was found to be rapidly condensed by 

 the coMer ethylene. One end of the thcrmo-elcmcnt was im- 

 mersed in the accumulated liquid inste.id of a ihcrinometer. 

 The temperature of the liquid when in regular ebullition, pro- 



NO. 1307, VOL. 51] 



duced by removing the cap protecting the lower half of the 

 cylinder, «as found to be - S9°'5 at 735 m.m. pressure. 



Liquid ethane cannot be sealed in a glass tube without con- 

 siderable danger. Hence the determinations of vapour pressure 

 and density were effected by the use of a modified Cailletet 

 compressing apparatus and spring manometer. The various 

 temperatures were obtained by surrounding the narrow thick- 

 walled glass tube in which the liquid was produced by suitable 

 baths. The critical temperature at which the curious cloudy 

 appearance was observed, just before the complete disappear- 

 ance of the liquid meniscus, was found to be 34'''S, and the 

 corresponding critical pressure 50 atmospheres. The meniscus 

 becomes hazy at 32" and only disappears completely at 40°, so 

 that the critical temperature, as in the case of propane, does 

 not appear to be so sharp as with many other liquids of low 

 boiling-point. The following table represents the vapoar 

 pressures lor a few intervals of temperature. 



Pressure in Pressure in 



Temperature, atmospheres. Temperature. atmospheres. 



-31" II o^ 23-3 



-20° 14-5 4-15° 32-3 



-11° iS-3 -f34°-5 so 



Prof. Dewar in 1SS4 determined the critical temperature and 

 pressure of ethane, and gave them as 35" and 45 '2 atmospheres. 

 M. Cailletet had previously stated that at -f 4" the gas exerted 

 a pressure of 46 atmospheres. Prof. Dewar's numbers are 

 now found to be in close accordance with Dr. llainlen's results, 

 and the older statement of M. Caillelet must therefore be taken 

 as founded upon an error. 



The density of liquid ethane was found to be o'446 at 0° and 

 0-396 at + io°"5. 



It may be interesting to compare the facts now established 

 with relerence to ethane and propane, with those previously 

 well ascertained for marsh gas and for normal butane. 



I 



Boiling point. 



Critical 

 tempeiature. 



Density in 

 liquid state. 



164 (Olszewski) — 8i-8(01s«wski) 54 9 0-4 is*' -■'4 

 •i6o(\Vroblcwski) - 959 (Dewar) ■ 50 

 Ethane C"H(t |— 89 "5 at 735 m.m. -f 34"5 so 1 0-446 at o 



Propane 0:tHs ;— 37'Q at 76oni.m. -hio2 48*5 0536 at o 



«-UutancCiHioi-h i — | — 060 at o 



' (RonaMsi865> 



If the above boiling-points are represented graphically alonjj 

 with those of the higher normal paraffins, molecular weight or 

 the number of carbon atoms being taken as absciss.-e and boiling- 

 point as ordinates, a perfectly regular curve is obtained, slightly 

 concave towards the axis of abscissa!, which very clearly indi- 

 cates the dependence of the boiling-point upon the molecular 

 weight. A. E. TUTio.N. 



THE BRITISH CENTRAL AFRICA 

 PROTECTORATE. 



lyr R. 11. II. JOHNSTONE opened the session of the Royal 

 •'■'■'■ Geographical Society on Monday evening with a jiaper on 

 liritish Central Africa, of which he is administrator. He con- 

 trasted the condition of the country ten years ago with what it 

 is now, explaining how the Mission schools, the .Scottish 

 planters, an 1 the Sikh police had produced changes in the 

 manners, productions, and means of tr.insport of the whole 

 region, and had succeeded in effectually repressing the slave 

 trade. A survey of the Protectorate has been in progress for 

 the last three years, and the map is beginning to acquire some 

 firmness of outline. The great advantage of the Protectorate 

 over the surrounding dislncls lies in the greater proportion of 

 high land over low swampy country. Roughly speaking, about 

 four-fifths of its land-surface is 3000 feet and upwards above the 

 level of the sea, and about onc-lifth is between 5000 and 10,000 

 feet. The immediate result of this elevation of the land is the 

 prevalence of a much cooler climate, than is usually found in 

 Central Africa so near the e<iuator. There arc portions of 

 British Central Africa where the heal is never oppressive, even 



