Septembee 24, 1915] 



SCIENCE 



429 



This volume deals with the technology and 

 industries of the products named, and their 

 analysis, also with the testing of lubricating 

 oils and greases, soaps, glycerine and candles. 

 A very important chapter is that on the waste 

 oils, fats and waxes, and the products derived 

 therefrom. 



The reviewer knows of no treatise which 

 deals so thoroughly with this phase of the 

 subject. The contents have been increased by 

 about twenty per cent., the principal additions 

 being made in the sections upon the examina- 

 tion of butter, hydrogenated fats, varnishes, 

 candles and soap. The work is encyclopedic, 

 no omissions being noted, and indispensable to 

 those having to deal with these compounds, or 

 industries, which are among the most impor- 

 tant. The reviewer would again take the 

 opportunity to urge the inclusion of an index 

 in each volume, as much increasing its con- 

 sulting value. 



A. H. Gill 



SPECIAL ASTICLES 



THE ABSORPTION OF AIE BY CHARCOAL COOLED TO 

 THE TEMPERATURE OF LIQUID AIR 



The remarkable absorption of certain gases 

 by charcoal cooled to the temperature of liquid 

 air, first pointed out by Kamsay and Soddy, 

 may be exhibited conveniently by either of 

 two simple pieces of apparatus. The first (A 

 in the figure) makes use of the electric dis- 

 charge as an index of the degree of absorption ; 

 while the second (B in the figure) indicates 

 the absorption by the barometric column sup- 

 ported in a vertical tube dipping into a bath 

 of mercury. 



The general form and dimensions of the 

 discharge-tube and its attached charcoal bulb 

 are indicated in A. The volume of the char- 

 coal used should be approximately equal to 

 that of the discharge tube proper. A vent 

 closed by a valve is included. Eor the experi- 

 ment to be in its best form the cocoanut char- 

 coal should be freshly burned, and to prevent 

 undue absorption of air when not in use the 

 tube should be partially pumped out and the 

 valve closed. The connections are made as 



shown in the figure, in which S is an alterna- 

 tive spark gap of about one centimeter length 

 in parallel with the discharge tube. Any in- 

 duction coil about the laboratory will answer. 

 To operate, open the valve, then close it 

 tightly, thus allowing the pressure within the 

 tube to become atmospheric. On starting the 

 induction coil the spark will pass at S. Now 

 gently submerge the charcoal bulb in liquid 

 air. In about one minute the spark at 8 will 

 begin to weaken and a stringy discharge will 

 appear between the electrodes of the discharge 

 tube. Soon the spark at S will cease while the 

 tube will be filled with the characteristic Geiss- 

 ler tube glow. In about four minutes the 

 walls of the discharge tube will begin to 

 flouresce, due to the bombardment of cathode 

 rays. The intensity of this fluorescence wiU 

 rapidly increase and soon the entire tube will 

 be uniformly filled with a beautiful apple- 

 green color. In about one minute more, five 

 . minutes from the start, the greenish color will 

 begin to fade and sparking will reappear at 8, 

 showing that the vacuum in the tube is be- 

 coming "hard." In short the pressure may 

 thus be reduced from atmospheric to about 

 .001 mm. mercury in five or six minutes with 

 no other agency than that of the absorption 



