1883.] 



On a " Rennet " Ferment. 



55 



become negative in the metal and liquid ones (viz., only 73 out of 286 

 in weak solutions, and 48 out of the same number in strong ones), 

 we may conclude that the metals more frequently than the liquids 

 have the greatest thermo-electric influence, and also that the relative 

 largeness of the number of instances of thermo-electro- positive metals 

 in the series of metals and liquids, as in the series of metals only, is 

 partly a consequence of the circumstance, that rise of temperature 

 usually makes substances, metals in particular, electro-positive. 

 These statements are also consistent with the view that the elementary 

 substances lose a portion of their molecular activity when they unite 

 to form acids or salts, and that electrolytes therefore have usually a 

 less degree of molecular motion than the metals of which they are 

 composed. 



The current from a thermo-couple of metal and liquid, therefore, 

 may be viewed as a united result of difference of molecular motion, 

 first of the two junctions, and second of the two heated (or cooled) 

 substances ; and in all cases, both of thermo- and chemico-electric 

 action, the immediate true cause of the current is the original 

 molecular vibrations of the substances, whilst contact is only a static 

 jDermitting condition. Also, that whilst in the case of thermo-electric 

 action, the sustaining cause is molecular motion supplied by an 

 external source of heat, in the case of chemico-electric action it is the 

 motion lost by the metal and liquid, when chemically uniting- 

 together. The direction of the current in thermo-electric cases 

 appears to depend upon which of the two substances composing a 

 junction increases in molecular activity the fastest by rise of 

 temperature, or decreases the most rapidly by cooling. 



In a separate paper " On some Relations of Chemical Corrosion to 

 Voltaic Currents," the author has investigated the amounts of external 

 voltaic current produced by the corrosion of known weights of 

 various metals at atmospheric temperature. 



V. "On a 'Rennet' Ferment contained in the Seeds of 

 Withania coagnlans." By Sheridan Lea, M.A., Trinity 

 College, Cambridge. Communicated by Professor M. 

 Foster, Sec. R.S. Received November 20, 1883. 



The Report of the Royal Gardens at Kew for 1881 contains 

 abstracts of correspondence, in which it was pointed out that, in 

 order to introduce a cheese- making industry in India, some vegetable 

 substitute must be found for the ordinary animal rennet, since cheese 

 made with the latter is unsaleable among the natives. In response to 

 the above " Surgeon-Major Aitchison brought to the notice of the autho- 



