1J42 



conglomeration due to the heating, a contraction of an originally 

 homogeneous film, in which very small microns probably already 

 existed, into larger particles. 



If we strongly heat a blue-green gold-precipitate (with a thin 

 flame against the back of the glass), then the hottest spot will turn 

 red with a gold reflection-colour, the colour roundabout being very 

 light to a somewhat darker yellow ; round this yellow colour it 

 turns blue again. Ultramicroscopically it appears that in this strongly- 

 heated place not much more conglomeration has set in. There is 

 still a similar mosaic as in the less intensely-heated places. In this 

 spot the gold is strongly fixed to the glass and as in this spot the 

 glass has been heated so as almost to get into a soft state, it seems 

 likely that the gold is diffused in it, partly solved. But this diffusion 

 cannot be very intense, for with acpia regia everything already gets 

 dissolved and only colourless glass remains. 



§ 6. Platinum. 



With evaporation it forms a more or less dark, greyish-black 

 precipitate, no selective absorption being visible. As the immeision- 

 liquid can loosen the precipitate from the wall, it was once more 

 covered in vacuum with Canadabalsam. 



Ultramicroscopically nothing is to be seen, except some very 

 dispersed, highly luminous large particles and a fairly large number of 

 weaker separate particles which may originate in the platinum, but as 

 appears from the experience with gold and silver they cannot 

 possibly be the bulk of the sublimated Ft. Only exceptionally do 

 we notice in between a weak Tindalleffect, which is distinctly visible 

 in some places only, where owing to the shorter distance between 

 filament, and wall a thicker precipitate had arisen. Hence the Ft 

 precipitate is optically insoluble. 



If we strongly heat the back of the glass with a thin flame, so 

 that the glass becomes soft, then the greyish precipitate on the 

 heated spot becomes yellowish-brown. (The heating was effected in 

 the air whereas the Ft was covered by a layer of CaF,). Around 

 it was a broad, annular zone, which was of a considerably lighter 

 grey than the surrounding field of non-heated platinum. 



Under tlie ultramicroscope it appeared once more that the heating 

 had effected the formation of ultramicrons. ^) 



Starting from the strongest-heated part to the non-heated part we 

 could observe very satisfactorily the transition : very strong network, 



1) Healing glass + GaFa alone, causes no change in the CaF^ 



