96 Scientific Intelligence. 



which yield two ions are bi-molecular whereas those which yield 

 three ions are monomolecular. K lister's experiments on naph- 

 thol and naphthalene are quoted by the author in support of his 

 views, as also the fact that many solid compounds have vapor 

 densities at low temperatures corresponding to a molecular mass 

 double that which they possess at high temperatures. — Ber. Berl. 

 Chem. Ges., xxxi, 130-187, February, 1898. g. p. B. 



7. On the Liquefaction of Hydrogen. — On the 1 0th of May, at the 

 Royal Institution, Dewar succeeded in effecting the complete lique- 

 faction of hydrogen. As early as 1896, he had successfully pro- 

 duced a jet of hydrogen containing liquid, by means of which 

 he was able to cool bodies below any temperature that could be 

 produced by liquid air. It was resolved therefore to construct a 

 larger apparatus of the same type, and the first experiments with 

 it were made on the above date. In his paper read to the Royal 

 Society on May 12th he says : " On May 10th, a start was made 

 with hydrogen cooled to — 205°C and under a pressure of 180 

 atmospheres escaping continuously from the nozzle of a coil of 

 pipe at the rate of about 10 to 15 cubic feet per minute in a 

 vacuum vessel double silvered and of special construction, all sur- 

 rounded with a space kept below — 200°C. Liquid hydrogen com- 

 menced to drop from this vacuum vessel into another doubly iso- 

 lated by being surrounded with a third vacuum vessel. In about 

 five minutes, 20 cc of liquid hydrogen were collected, when the 

 hydrogen jet froze, up from the solidification of air in the pipes. 

 The yield of liquid was about one per cent of the gas. The 

 hydrogen in the liquid condition is clear and colorless, showing no 

 absorption spectrum, and the meniscus is as well defined as in the 

 case of liquid air. The liquid must have a relatively high refractive 

 index and dispersion and the density must also be in excess of the 

 theoretical density, viz., 0'18 to 012, which we deduce respectively 

 from the atomic volume of organic compounds and the limiting 

 density found by Amagat for hydrogen gas under infinite com- 

 pression." . . . "Not having arrangements at hand to determine 

 the boiling point, two experiments were made to prove the exces- 

 sively low temperature of the boiling fluid. In the first place, 

 when a long piece of glass tubing sealed at one end and open to 

 the air at the other was cooled by immersing the closed end in the 

 liquid hydrogen, the tube immediately filled where it was cooled 

 with solid air. The second experiment was made with a tube 

 containing helium." . . . " Having a specimen of helium which 

 had been extracted from Bath gas sealed up in a bulb with a nar- 

 row tube attached, the latter was placed in liquid hydrogen, when 

 a distinct liquid was seen to condense. From this result it 

 would appear that there cannot be any great difference in the boil- 

 ing points of helium and hydrogen." Although Olszewski has pub- 

 lished an account of experiments in which hydrogen was obtained 

 in a state of momentary or " dynamical " liquefaction, as a thin 

 mist, in which state some of its constants were measured, 

 Dewar's result, in which the hydrogen was produced as a "static" 



