CORRECTION OF THE VOLUMES OF GASES FOR TEMPERATURE AND PRESSURE. Law of Charles: Gases under constant pressure expand part of their volume at o° C. for every increase in temperature of 1° C. Thus 273 volumes of any gas at o° C. become 274 دو دو 1° C. 2° C. This fraction 173, or the slightly more accurate decimal fraction 0003665, is termed the coefficient of expansion of gases. EXAMPLES. I. Io c.c. of a gas are measured at 15° C. What volume will the gas occupy at 150° C. ? 2. 100 c.c. of hydrogen are measured at 100° C. How many cubic centimetres will the gas occupy at · 100° C. ? 3. What will be the volume at 25° C. of 252 c.c. of oxygen measured at 15° C. ? I + (15 × 0003665): 1 + (25 X 0·003665) :: 252 : x 1054975: 1091625:: 252 : x By increasing the pressure upon a gas its volume is diminished by diminishing the pressure the volume is increased. Boyle's Law:-The volume of a gas at constant temperature is inversely proportional to the pressure to which it is subjected. I. 1000 c.c. of hydrogen are measured under a barometric pressure of 740 mm. What will the volume become under the standard pressure of 760 mm. ? 2. A litre of air is measured at o° C. and 760 mm. What volume will it occupy at 740 mm. and 15°5 C.? Dalton's Law of Partial Pressures :-The pressure of a mixture of chemically indifferent gases and vapours is equal to the sum of the pressures which each would exert if it alone occupied the whole space. EXAMPLES. 1. If 100 vols. of air consist of 20'66 0, 779 N, 0°03 CO2, and 140 of aqueous vapour, and the barometer stands at 760 mm. ; what is the partial pressure of each of these vapours and gases? The pressure of a vapour in contact with its own liquid is always the same at the same temperature. 2. An eudiometer, graduated in mm. from the closed end, contains coal gas; pure boiled water is introduced until the mercury meniscus remains wet; the upper level of the mercury with gas dry stands at 400 mm., the lower level at 800 mm. ; the average volume of 1 cm, of the tube 166 c.c., barometer stands at 756 mm., temp. of air is 18°C. What are the volumes of the dry coal gas and of the vapour of water in the moist gas respectively, reduced to standard conditions? = = Vol. of dry coal gas · 1·66 × 40′0= 66°4 c.c. at 756 – (800-400) or 356 mm. and 18°C. Hence vol. at o°C. and 760 mm. = 66.4 × 356 × 273 760 × 291 = 29'18 c.c. Tension of aqueous vapour at 18°C. 15'33 mm. ; hence upper level of mercury is depressed to (400 X 15'33) mm. and vol. of aqueous vapour 166 × 41°536 = 68.95 c.c. at 15°33 mm. and 18°C., and this volume of a gas 68.95 X 15'33 X 273 760 X 291 = QUESTIONS. 37. 170 volumes of oxygen are measured at 10°C. What will the volume be on the temperature sinking to o°C. ? 38. A certain weight of air measures a litre at o°C. How much will the air expand on being heated to 100°C.? 39. A gas has its temperature raised from 15° C. to 50° C.; at the latter temperature it measures 15 litres. What was the initial volume? 40. A volume of hydrogen measures 1500 cubic centimetres at o° C. How many cubic centimetres will it measure at (a) 15°5 C., (b) at 50° C., (c) at 100° C., and (d) at 300° C.? At what temperature will it measure exactly 1000 cubic centimetres? 41. The coefficient of expansion for gases for 1° C. is 0003665. What is the coefficient for (a) 1° F., and (b) 1° R.? 42. A certain volume of air preserved at a constant temperature measures 150 cubic centimetres when the barometer stands at 760 millimetres. On the following day its volume is found to have decreased 152 cubic centimetres. Calculate the alteration in the height of the barometer which must have ensued. 43. A balloon containing 1200 cubic metres of coal gas under a pressure of 770 millimetres of mercury ascends until the barometer stands at 530 millimetres. What volume would the gas in the balloon now occupy supposing none to have escaped? 44. A certain quantity of nitrogen measures 155 cubic centimetres at 10° C., and under a pressure of 530 millimetres of mercury. What will the volume become at 18°.7 C., and under a pressure of 590 millimetres of mercury. 45. Calculate the temperature at which air possesses a density equal to that of hydrogen at o° C. 46. Oxygen is passed into an eudiometer till the upper level of the mercury stands at 250 mm., level in trough at 780 mm. It is required to add double the quantity of hydrogen; if the tube be adjusted till the trough level becomes again 780 mm. and the average volume of 10 mm. of tube is 174 c.c., what will be the reduced volume of the added hydrogen, and what the reading of the upper level of the mercury in the eudiometer after the addition (Bar. 754 mm., T. 17.5° C.)? 47. Supposing the atmosphere to be saturated at 15° C., barometer 754 mm., what is the per centage volume of aqueous vapour contained in the air? 48. Defining the dew-point as the temperature at which the air would be saturated when containing the amount of vapour of water present at the time of observation, give the per centage volume of aqueous vapour present in the air when the dew-point is 15° C. and 5° C. respectively (Bar. 765 mm.). 49. A gas burette contains 53°2 c.c. of moist coal gas at 760 mm. pressure and 18.5° C.: find the volume of the dry gas under standard conditions. 50. 23'70 c.c. of dry nitrogen are contained in an absorptiometer, 5 c.c. of water are introduced and by agitation o'07 c.c. of the gas is absorbed. The pressure is brought to that of the atmosphere, 757°3 mm., when reading the volumes, and the temperature remains at 16° C. what is the volume of moist nitrogen indicated at the end of the experiment? RELATIVE DENSITY OF SOLIDS, LIQUIDS, AND GASES; VAPOUR DENSITY. THE specific gravity (sp. gr.) or relative density of a solid or liquid substance is the ratio of its mass to the mass of an equal volume of some liquid taken as unity. The standard universally adopted is pure water at its maximum density. The number which expresses the relative density of a solid or liquid substance denotes, therefore, how much heavier or lighter the substance is than an equal bulk of water at 4° C. 1. The relative density of a solid is generally ascertained by : where w = Weight of substance (W) weight of substance in water at 4° C. If the solid be lighter, bulk for bulk, than water a sinker is employed of weight in water = x, and rel, dens. = d. where w' = weight of combination in water. C |