1139 



feeding-wires, which was covered witli CaF,. By bringing this wire 

 into a state ol' incandescence the salt coidd be sublimated. As the 

 layer of salt does not sufficiently protect the undei-lying metal from 

 the subsequent effect of the immersion-liquid (glycerine), it was in 

 its turn covered as well with a layer of Canadabalsam (^in the vacuum). 



The pi-ecipitate we tested had been brought on the glass under a 

 temperature of liquid air. The part that had been covered with 

 CaFj as well as with Canadabalsam, remained perfectly unaltered 

 with access of air and under the microscope it revealed a weak 

 mosaic. In spite of all the precautions taken, the out-crystallisation 

 could not be hindered. 



Where no second covering with Canadabalsam had been applied, 

 the access of the immersion liquid (glycerine) caused a change of 

 colour in the deposit (blue— > brownish red) and the ultramicroscopic 

 image was much richer in ultramicrons and the ultramicrons themselves 

 became stronger. Hence CaF, by itself did not sufficiently protect. 



Injiuence of Temperature. 



With our first investigations it had already been observed that 

 short heating at a comparatively low temperature, say 260" already 

 causes obvious alterations in the deposit of silver, revealing themselves 

 both in change of colour and in a coarsening of the deposit. 



These alterations become distinctly apparent, on locally heating 

 the precipitate formed under room temperature, by momentarily 

 pressing a very hot glass rod against the outside of the glass wall. 

 In the homogeneous blue Held the heated place then stands out as 

 a red spot, in a red field as a j'ellow one. This change sets in, not 

 only in the unopened evacuated lamp, but also when the silver is 

 in contact with the air or is covered with a layer of Canadabalsam. 



If the glass-shard on which such a spot arises, is moved across 

 the field of vision of the microscope, it appears, that whereas the 

 non- heated part consists of a mosaic of but very weak ultramicrons, 

 the heated part presents an exceedingly luminous field of vision. 

 The primary colour of the fields observed in the microscope is always 

 complementary to that which is observed with the naked eye. 

 Though the distance of the separate particles has not perceptibly 

 altered, yet the pai'ticles themselves are much more luminous and 

 it also seems as if the layer of the luminous particles has become 

 thicker. 



Hence the separate ultramicrons have increased in size and probably 

 in number too, at the ex pence of a quantity of silver, which at first 

 was invisible. 



79 



Proceedings Royal Acad. Amsterdam. Vol. XX 



