Til Sdt ntific I nt, II i ij, nee. 



5, Practical Physiological Chemistry/ by Philip B. Hawk - . 

 Fifth Edition. Pp. xiv, 638. Philadelphia 1916 (P. Blakiston's 



Son A- Co.; price, 12.50). — The latest edition of this widely used 

 manual 1ms experienced very substantial enlargement by the 

 addition of descriptions of new chemical methods applicable to 

 biochemical analysis. Chapters on Nucleic Acids, Intestinal 

 Digestion, Blood Analysis and Metabolism have been added. 

 The directions for conducting metabolism experiments under 

 laboratory conditions represent a somewhat novel and useful addi- 

 tion to a book of this character. The descriptions of procedures 

 continue, as in the earlier editions, to be presented with accuracy 

 and sufficient detail to serve as a useful basis for practical work. 

 Even cursory examination of the analytical technic or demonstra- 

 tion procedures selected shows that the volume is an up-to-date 

 product. l. b. m. 



6. The Ionization and Dissociation of Hydrogen. — It has 

 been shown by J. J. Thomson that in a discharge tube contain- 

 ing hydrogen there are present charged atoms, charged molecules, 

 and sometimes a constituent having a mass three times that of the 

 hydrogen atom. The pressure used was about 0-003'" 1 " of mer- 

 cury and the necessary potential difference was of the order of 

 20,000 volts. A different experimental method of obtaining posi- 

 tive rays has been recently devised and successfully employed \>y 

 A. J. Dempster. The electrons leaving a Wehnelt cathode were 

 accelerated by the field between this electrode and the anode. 

 The electrons ionized the gas between the electrodes and thus 

 produced positive particles which acquired a sufficiently great 

 velocity to carry them past the edge of the cathode (2 ,ura wide) 

 and thence through a hole of small diameter which had been 

 made in a screen. This screen was roughly normal to the electric 

 field and parallel to the axis of a magnetic field which could be 

 established at will between the poles of an electromagnet placed 

 opposite to the emergence end of the hole. The north and south 

 pole pieces also served respectively as the negative and positive 

 ends of an electrostatic field. After passing through these two 

 superposed deviating fields the positive particles fell upon another 

 screen in which a suitably-disposed parabolic slit had been cut. 

 By properly adjusting the deviating fields the parabolas corre- 

 sponding to each constituent of the beam of positive particles 

 could be brought successively into coincidence with the slit. 

 After passing through the curved slit the particles entered a 

 Faraday chamber and recorded their charges in the usual way. 

 The advantages afforded by the Wehnelt cathode are that low 

 potentials may be used, and that the pressure of the gas may be 

 made as small as desired and may also be varied without chang- 

 ing the potential. 



Three diagrams are shown in the paper, each having the strength 

 of the deflecting magnetic field plotted along the axis of abscissas 

 with the charge on the Faraday chamber as ordinates. The first 

 curve corresponds to 800-volt rays produced in hydrogen at a 



