THE SO-CALLED INORGANIC ENZYMES 121 



The catalytic action of finely divided metals was taken up 

 by Bredig and Miiller von Berneck, and tested in the case of 

 platinum and hydrogen- peroxide. For this purpose, finding 

 platinum black difficult to subdivide and suspend in solution, 

 they evolved the ingenious method of obtaining the platinum in 

 colloidal solution. Colloidal solutions of metals had already been 

 prepared by Carey Lea by chemical means, such as colloidal silver 

 by reduction of silver nitrate by ferrous sulphate ; but Bredig dis- 

 covered the much simpler method of detaching the metal from the 

 negative electrode by means of a high potential in distilled water. 



The process consists in establishing an electric arc between stout 

 metallic electrodes of the metal of which it is desired to make a 

 colloidal solution, in as pure as possible distilled water, which must 

 be maintained at a low temperature. The conductivity of the water 

 must be low, or otherwise electrolytic conductivity comes in and 

 destroys the process, and, further, the presence of electrolytes tends 

 to precipitate the colloidal metal. 



The process can be best carried out by utilising the electric 

 lighting mains (the usual 110 volt, constant current, circuit), and 

 placing in the circuit an ammeter, a flat crystalling dish containing 

 about 100 c.c. of pure distilled water which has previously been 

 boiled to expel dissolved carbon- dioxide, and a variable fluid resist- 

 ance which is regulated to give a current of 4 or 5 amperes after 

 the electric arc has been established under the distilled water. The 

 electrodes consist of stout platinum, gold, or silver wire from 1 to 2 

 millimetres in diameter, and can either be passed through two glass 

 tubes so as to be easily handled, or sealed into two glass tubes which 

 are filled with mercury by means of which electric contact is made 

 with the platinum. 



In using the apparatus a short circuit is made between the two 

 electrodes under the distilled water, and then separated, when an 

 electric arc is established, and glows beneath the water ; minute 

 particles of metal are now detached from the negative pole, some 

 of which pass to the positive pole, but others remain in the distilled 

 water and form an exceedingly fine suspension or colloidal solution 

 of the metal. 1 



The electric arc frequently breaks down on account of variations 

 in resistance, when it must be established as before. 



1 That the metal comes from the kathode was shown by Bredig by weighing 

 the electrodes before and after use, when a loss was found in the kathode, and 

 a gain of less amount in the anode. 



