434 On the Experimental Relations [1857. 



solution, a ruby jelly is generally produced. In such ruby 

 jelly the reduced particles of gold preserve their state and 

 relative place, and the tint does not pass to blue, even though 

 a considerable proportion of salt be present. Such jelly will 

 remain in the air for weeks before it decays, and has every 

 character, in colour and appearance, of gold ruby glass. It is 

 hardly possible to examine the series of ruby glass, ruby mem- 

 brane, ruby jelly cold and gelatinous, ruby jelly warm and 

 fluid, and the ruby fluids, to consider their production, and 

 then to conclude that the cause of their common ruby colour is 

 not the same in all. 



When the warm ruby jelly is poured into a capsule or on to 

 a plate, allowed to gelatinize and then left in the air, it gra- 

 dually becomes dry. When dry, some of these jellies remain 

 ruby ; others will probably be of an amethystine violet colour, 

 or perhaps almost blue. When one of the latter is moistened 

 with water, and has absorbed that fluid, it becomes gelatinous, 

 and whilst in that state resumes its first ruby colour ; but on 

 being suffered to dry again, it returns to its amethystine or blue 

 colour. This change will occur for any number of times, as 

 often as the jelly is wetted and dried. Here the gold remains 

 in the same metallic state through this great change of colour, 

 the association or the absence of water being the cause : and 

 the effect strengthens in my mind the thought before expressed, 

 that in the ruby fluids the deposited particles are frequently 

 associates of water and gold. It is a striking case of the joint 

 effect of the media and the gold in their action on the rays of 

 light, and the most striking case amongst those where the 

 medium may be changed to and fro. 



When a ruby jelly is prepared with salt, and being warm is 

 poured out in thin layers on to glass or porcelain, it first gela- 

 tinizes and then dries up ; in which case the salt is excluded 

 and crystallizes. When the dry jelly is put into cold water, the 

 salt dissolves and can be removed. The jelly then swells to a 

 certain amount, after which it can be left soaking in water for a 

 week or longer, until everything soluble is separated. No 

 change takes place in the ruby tint, no gold is removed. When 

 the last water is poured off and the remaining jelly warmed, it 

 melts, forming a fine ruby fluid, which can either be dissolved 

 in more water, or regelatinized, or be dried and preserved for 



