434 HYDROGEN The general disposition of M. Pictet s apparatus is seen in fig. 3. It is oT a much more complex character, but permits of the ex periment being made on a comparatively very large scale. The condensation of the gas is effected in a copper tube of narrow bore, FIG. 3. Pictet s Apparatus for Liquefaction of Gases. connected at the one end with a manometer capable of indicating pressures up to 800 atmospheres, and with a fine steel stop-cock, and at the other with a very strong wrought-iron vessel in which the hydrogen is generated by heating a perfectly dry mixture of potassium formate with potassium hydroxide ; these two substances enter into reaction in accordance with the equation HCOOK + HOK = K 2 C0 3 + H 2 , the hydrogen being evolved in a perfectly regular manner when the temperature ismaiutained at 225. The dimensions of the condensation tube are internal diameter 001 metre, exter nal diameter 015 metre, length 4 "16 metres ; and the retort has a capacity of 1659 cubic centimetres. The charge introduced con sisted of 500 grammes potassium hydroxide and 1251 grammes potassium formate. The condensation tube is surrounded with a wider tube containing condensed carbon dioxide or nitrous oxide; these tubes are enclosed in the lower box seen in the sketch. The upper box contains a tubular arrangement in which carbon dioxide or nitrous oxide from the gasholder is reduced to the liquid state. The pumps are such as are used in ice-making machines, one of each pair being an exhausting, the other a condensing pump; one pair of these pumps is employed in condensing and volatilizing the sulphur dioxide, and the other in condensing and volatilixing the carbon dioxide or nitrous oxide. Figs. 4 and 5 show the appa ratus in vertical section and in plan. In working the apparatus, in the first place liquid sulphur dioxide fro7ii the reservoir seen between the first pair of pumps is charged into the outer tube of the condenser in the upper box, and is caused rapidly to evaporate by the action of the exhausting pump in con nexion with the tube, while the other pump serves to recondense it in the reservoir, which is a kind of tubular boiler provided with a cold water circulation. The temperature of the liquid sulphur dioxide is thus reduced to - 65 C. ; on allowing the carbon dioxide or FIG 4. Vertical Section of Pictet s Apparatus. nitrous oxide to enter the inner tube of the condenser thus cooled, it begins to liquefy under a pressure of about 4 atmospheres, and the condensation of the whole of the gas is effected at a pressure of from 4 to 7 atmospheres, the temperature of the liquid sulphur di oxide fluctuating between - 65 and - 50. The liquid carbon dioxide (or nitrous oxide) thus obtained is then allowed to pass into the tube surrounding the condensation tube, and by the action of the second exhausting pump it is caused to evaporate so quickly that it solidi fies. The temperature may thus be reduced to - 120 or even - 140. In describing his first experiment with hydrogen with this appa ratus, M. Pictet states that the pressure, having risen gradually during about 40 minutes, became stationary at about 650 atmo spheres ; on then opening the stop-cock, the orifice being illumi nated by a powerful electric light, an opaque jet of a highly char acteristic steel-blue tint was seen to issue forth. At the same moment, a sharp hissing noise like that produced on plunging a red- hot bar of iron into water was heard, and simultaneously a highly FIG. 5. Plan of Pictet s Apparatus characteristic rustling noise on the ground, recalling the sound of small seed falling. Moreover, the jet was not continuous as in the case of oxygen, but intermittent, each projection of matter being attended with the peculiar rustling noise alluded to; in fact, owing to the great reduction in temperature, due to the sudden volatilization of the liquid, portions became solidified in the tube. On closing the stop-cock after several seconds, the pressure being still 370 atmo spheres, the pressure fell to 320 atmospheres, then slowly rose to 330 atmospheres, and remained constant for several minutes ; on now opening the stop-cock again, a jet issued of extremely short duration, accom panied with the violent projection of solid particles, but then nothing escaped although the pressure was 315 atmospheres, an indication that the hydrogen had solidified in the interior of the tube. On ceasing to aspirate from the tube surrounding the condensation tube, and thus allowing the temperature of the latter to rise somewhat, discharges took place with increasing frequency, until after about a quarter of an hour the pressure fell to zero. Pictet thus succeeded in liquefying and solidifying hydrogen on January 10th, 1878, Cailletet having demonstrated its liquefaction
on December 30th previously.
