390 Scientific Intelligence. 



5 or 6 centimeters of this tube remained filled with the gas when 

 the liquefying point was reached. A carefully compared Baudin 

 thermometer was plunged in a cylinder of water enclosing the 

 tube, the temperature of which could be altered at will. Careful 

 regulation of the pressure enabled the phenomena of appearance 

 and disappearance, of the meniscus to be produced within 1°. 

 For hydrogen chloride the critical temperature was found to be 

 51 '5°, the critical pressure 96 atmospheres. Methyl chloride may 

 be compressed to 200 atmospheres at 142° without the appearance 

 of a meniscus; but at 141°, the liquid is distinctly seen. The 

 critical temperature is then ] 41 "5° and the pressure 73 atmospheres. 

 Ethyl chloride has its critical point at 182*5° and at 54 atmospheres. 

 Ammonia gas has a critical temperature of 131° and a pressure of 

 113 atmospheres; corresponding closely with the values obtained 

 by Dewar, 130° and 115 atmospheres. The critical point observed 

 for monomethylamine was 155°, for dimethylamine 163°, and for 

 trimethylamine 160 - 5°; the corresponding pressures being 72, 56 

 and 41 atmospheres respectively. Comparing the above temper- 

 atures with each other, it appears that while they progressively 

 increase with the molecular complexity, their differences diminish. 

 Comparing them with the critical pressures, it will be noticed 



273 +T . 

 that they vary inversely as these pressures, the value — ^ — in- 

 creasing slowly as the size of the molecule increases ; contrary to 

 the results obtained by Dewar for the simpler gases in which 

 both pressure and temperature increased together. His figures 



273-J-T 

 show that the ratio - — ~— is nearly constant and has a mean value 



of 3 "5. The values of the present paper are for hydrogen chloride 

 and ammonia 3*4. and 3-5 respectively; while methyl chloride 

 gives 5*7, ethyl chloride 8*4, monomethylamine 5'9, dimethyl- 

 amine 7*9, and trimethylamine 10"5. — J. Physique, II, v, 58, Feb- 

 ruary, 1886. G. F. B. 



2. On the Double Refraction produced by Metallic films. — 

 Kttndt, desiring to prepare transparent films for his investiga- 

 tions on the rotatory magnetic polarization of the metals, made 

 use of the method of Wright* lor this purpose; i. e., showering 

 down the material forming the negative electrode upon a glass 

 plate in an exhausted receiver. But when the films thus prepared 

 were placed between two crossed Nicol prisms he was surprised 

 to find them double refracting. This phenomenon was observed 

 with platinum, palladium, gold, silver, iron and copper. If the 

 cathode is placed perpendicularly to the glass plate the deposit is 

 slightly conical; so that when placed between the two Nicols, in 

 parallel light, a black cross is seen in a bright field, the arms of 

 which correspond with the planes of polarization of the Nicols. 

 Kuudt has shown that this effect caunot be due to the conical 

 form of the deposit, to a state of tension of the metallic film, nor 



* This Journal, III, xiii, 49, Jan.; xiv, 169, Sept., 1877. 



