68 



THE MECHANISM OF LIFE 



sulphate. At the Congress of Rheims in 1907 I exhibited the 

 result of some further experiments on the same subject. 



These periodic precipitates may be obtained from a great 

 number of different chemical substances. The following is 

 the best method of demonstrating the phenomenon. A glass 

 lantern slide is carefully cleaned and placed absolutely level. 

 We then take 5 c.c. of a 10 per cent, solution of gelatine and 

 add to it one drop of a concentrated solution of sodium 

 arsenate. This is poured over the glass plate whilst hot, and 

 as soon as it is quite set, but before it can dry, we allow a 

 drop of silver nitrate solution containing a trace of nitric 



acid to tall on it from 

 a pipette. The drop 

 slowly spreads in the 

 gelatine, and we thus 

 obtain magnificent 

 rings of periodic pre- 

 cipitates of arsenate of 

 silver, with which any 

 one may easily repeat 

 the experiments de- 

 tailed in this chapter. 

 Circular Waves of 

 Precipitation. — The 

 wave-front of the peri- 

 odic rings of precipi- 

 tates is always perpendicular to the rays of diffusion. The 

 distance between the rings depends on the concentration of 

 the diffusing solution. The greater the fall of concentration, 

 the less is the interval between the rings. Each ring repre- 

 sents an equipotential line in the field of diffusion. These 

 equipotential lines of diffusion give us the best and most 

 concrete reproduction of the mode of propagation of periodic 

 waves in space. They are, in fact, a visible diagram of 

 the propagation of the waxes of light and sound. Occasion- 

 ally we may observe in the gelatine the simultaneous pro- 

 pagation of undulations of different wave-length, just as we 

 have them in the ether and the air. These diffusion wavelets 



Fig. 12 — Lines of diffusion precipitate, showing 

 the simultaneous propagation of undulations 

 of different wave-length. 



