424 On the Experimental Relations [1857. 



0'7 of a grain of metal, was made up to 70 cubic inches by the 

 addition of distilled water and converted into ruby fluid : on 

 the sixth day it was compared with the ruby glass standard, 

 and with a depth of 1*4 inch was found equal to it ; there was 

 just one hundredth of a grain of geld diffused through a cubic 

 inch of fluid. In another comparison, some gold leaves were 

 dissolved and converted into ruby fluid, and compared ; the 

 result was a fluid, of which 1'5 inch in depth equalled the 

 standard, a leaf of gold being contained in 27 cubic inches of 

 the fluid. Hence looking through a depth of 2*7 inches, the 

 quantity of gold interposed between the light and the eye 

 would equal that contained in the thickness of a leaf of 

 gold. Though the leaf is green and the fluid ruby, yet it is 

 easy to perceive that more light is transmitted by the latter 

 than the former ; but inasmuch as it appears that ruby fluids 

 may exist containing particles of very different sizes (or that 

 settle at least with very different degrees of rapidity), so it is 

 probable that the degree of colour, and the quantity of gold 

 present, may not be always in the same proportion. I need 

 hardly say that mere dilution does not alter the tint sensibly, 

 f. e. if a deep ruby fluid be put into a cylindrical vessel, and 

 the eye look through it along the axis of the vessel, dilution 

 of the fluid to eight or ten times its volume does not sensibly 

 alter the light transmitted. From these considerations, it 

 would appear that one volume of gold is present in the ruby 

 fluid in about 750,600 volumes of water ; and that whatever 

 the state of division to which the gold may be reduced, still 

 the proportion of the solid particles to the amount of space 

 through which they are dispersed, must be of that extreme 

 proportion. This accords perfectly with their invisibility in 

 the microscope ; with the manner of their separation from the 

 dissolved state ; with the length of time during which they can 

 remain diffused; and with their appearance when illuminated 

 by the cone of the sun's rays. 



The deposits, when not fixed upon glass or paper, are much 

 changed by drying ; they cannot be again wetted to the same 

 degree as before, or be again diffused ; and the light reflected 

 or refracted is as to colour much altered, as might be expected. 

 Whilst diffused through water, they seem to be physical asso- 

 ciations of metallic centres with enveloping films of water, and 



