134 PRINCIPLES OF CHEMISTRY 



follow from Marietta's law. 28 From tins it may be concluded 

 that the absolute boiling point of hydrogen, and of gases resembling 



saturated vapours takes place. The temperatures (according to the air thermometer) 

 are placed on the left, and the tension in millimetres of mercury (at ) on the right, 

 hand side of the equations. Carbon bisulphide, CSg, = 127'9; 10 = 198'5; 20 = 298*1; 

 30 = 431-6; 40 = 617'5; 50 = 857'1. Chlorobenzene, C C H 5 C1, 70 = 97'9; 80 = l-il'8; 

 90 = 208'4; 100 = 292'8; 110 = 402-6; 120 = 54t2'.s; 13u- = 71iK). Aniline, C 6 H 7 N, 

 150 = 283-7; 160 = 887-0; 170 = 515-6; 180 = 677"2; LS.V =771-5. Methyl sulicylate, 

 C 8 H 8 O 5 , 180 = 249-4; 190 = 330'9; 200 = 432'4; 210 C = 557'5; 220 C = 710"2; 224' : =77i".. 

 Mercury, Hg, 300 = 246'8 ; 310 = 304'9 ; 320 = 373'7 ; 330 = 454'4; 340 = 548-6; 

 350 = 658'0; 359 = 770'9. Sulphur, S, 395 = 300; 423 = 500; 443 =-700 ; 452 = 800 ; 

 459 = 900. These figures (Ramsay and Young) show the possibility of fixing con- 

 stant temperatures in the vapours of boiling liquids. The tension of liquefied 

 gases is expressed in atmospheres. Sulphurous anhydride, SO> bO c = 0'4 ; 20 = 0*6; 

 -10 = 1; = 1'5; +10 = 2'3; 20 = 3'2; 30=5'3. Ammonia, NH 5 , -40 = 0'7; 

 -30 = 1-1; -20 = l-8; -10 = 2'8; = 4'2; + 10 = 6'0; 20 = 8'4. Carbonic anhydride, 

 CO 2 , -115 = 0-033 ; -80 = 1; 70 = 2'1; -60 = 3'9 ; -50 = 6'8 ; -40 = 10; -20 = 23; 

 = 35; +10 = 46; 20=58. Nitrous oxide, N 2 O, -125 = 0'033 ; -92 = 1; -80 = 1'9; 

 -50 = 7-6; -20 = 23-1; = 36'1; +20 = 55'3. Ethylene, CoH 4 , -140 = 0'033; 

 -130 = 0-1; -103 = 1; -40 = 13; -1 = 42. Air, -191 = 1; -15~8 = 14; -140 = 39. 

 Nitrogen, N 2 , -203 = 0'085; -193 = 1; -160 = 14; -146 = 32. The methods of 

 liquefying gases (by pressure and cold) will be described under ammonia, nitrous oxide, 

 sulphurous anhydride, and in later footnotes. We will now turn our attention to the 

 fact that the evaporation of volatile liquids, under various, and especially under low r 

 pressures, gives an easy means for obtaining low temperatures. Thus liquefied carbonic 

 anhydride, under the ordinary pressure, reduces the temperature to - 80 3 , and when it 

 evaporates in an atmosphere rarefied (in an air-pump) to 25 mm. ( = 0'033 atmospheres) 

 the temperature, judging by the above-cited figures, falls to -115 (Dewar). Even the 

 evaporation of liquids of common occurrence, under low pressures easily attainable in an 

 air-pump, may produce low temperatures, which may be again taken advantage of for ob- 

 taining still lower temperatures. Water boiling in a vacuum becomes cold, and under 

 a pressure of less than 4'5 mm. it freezes, because its tension at is 4'5 mm. A 

 sufficiently low temperature may be obtained by forcing fine streams of air through 

 common ether, or liquid carbon bisulphide, CS 2 , or methyl chloride, CH 3 C1, and other 

 similar volatile liquids. In the adjoining table are given, for certain gases, (1) the 

 number of atmospheres necessary for their liquefaction at 15, and (2) the boiling points 

 of the resultant liquids under a pressure of 760 mm. 



C 2 H 4 N a O CO., H.,S AsH 3 NH* 3 HC1 CH 3 C1 CLX, SO, 



(1) 42 31 52 10 8 7 25 4 4 3 



(2) -103 -92 -80 -74 -58 -38 -35 -24 -21 -10 



28 Natterer's determinations (1851-1854), together with Amagat's results (1880-1888), 

 show that the compressibility of hydrogen, under high pressures, may be expressed by 

 the following figures : 



p. 1 100 1000 2500 



v I 0-0107 0-0019 0-0013 



2W 1 1-07 1-9 3-25 



s 0-11 10-3 58 85 



where p = the pressure in metres of mercury, v = the volume, if the volume taken under 

 a pressure of 1 metre =1, and s the weight of a litre of hydrogen at 20 in grams. If 

 hydrogen followed Mariotte's law, then under a pressure of 2500 metres, one litre would 

 contain not 85, but 265, grams. It is evident from the above figures that the weight of 

 a litre of the gas approaches a limit as the pressure increases, which is doubtless the 

 density of the gas when liquefied, and therefore the weight of a litre of liquid 

 hydrogen will probably be near 100 grams (density about O'l, being less than that of all 

 other liquids). 



