of Edinburgh, Session 1879-80. 
713 
retained their exact original form, yet the carbon found its way to 
a considerable distance into the crucible, and some of the particles 
penetrated the crucible throughout. This was not a case, therefore, 
of fusion and mechanical mixture. 
On examining a section of the crucible under the microscope, the 
particles of carbon can be distinctly seen disseminated through the 
silica and alumina of the crucible, and thickest in the glaze and 
outer parts which are nearest to the carbon. We also notice a 
number of “ tricites” all along the juncture of the alumina with the 
glaze of the crucible, arising from the devitrification of the glaze, 
and a number of particles of larger size which are contained in the 
original crucible. On examining a section of the crucible before 
being used we see nothing in the form of little black particles dis- 
seminated throughout, and are thus able to recognise more com- 
pletely these black specks as carbon, the result of diffusion. 
JSTow carbon, so far as we know, has no chemical action on silica 
or alumina, and consequently it cannot have been taken into the 
crucible by chemical action. This, then, is a distinct case of the 
diffusion of an impalpable powder into a solid body in a softened state. 
And it has the advantage that, the solid body being transparent, we 
can, by examining it with the microscope, see what has actually 
taken place. And here it gives us an insight into another matter. 
It is evident that this is precisely what takes place in the conversion 
of bar iron into steel by the cementation process. The carbon in 
the state of an impalpable powder diffuses into the bars of iron 
whilst they are in the softened state, the operation taking a number 
of days before it is completed. Thus it seems to me to explain the 
up to the present time unsettled question of the conversion of iron 
into steel by the cementation process, and to render unnecessary the 
“ Occlsuion of Gases” theory. 
In order to make absolutely certain of the fact that carbon had 
really penetrated into the crucible, I took a portion of the crucible, 
pounded it down, and treated it with hydrofluoric acid for some days. 
I then filtered off the insoluble residue which was left, and after 
treating it successively with hydrochloric acid and soda, ultimately, 
on largely diluting, got the carbon (in an exceedingly fine state) 
suspended in the water, and by decantation, and filtering the 
decanted fluid, got it on to a filter. Its quantity, however, in this 
