228 
Dr. Thomson on some of 
with water. It became milky, and deposited a small quantity 
of white matter, which possessed the following properties : 
Its colour was white, it was tasteless, and insoluble in 
water : it dissolved in muriatic acid, and was again precipi- 
tated by dilution. When digested in caustic potash it became 
black. This black matter again dissolved slowly in muriatic 
acid, and was precipitated white by potash. I had never 
more of it at once than half a grain. It seems to be a 
metalline salt. The characters agree best with a salt of base 
of manganese. The acid is neither the chromic, phosphoric, 
nor arsenic. This matter existed in all the specimens of 
chrome iron ore that I examined. The muriatic solution thus 
freed from the white matter was precipitated by caustic 
ammonia. The peroxide of iron after washing and ignition 
was dissolved in muriatic acid, to separate a little silica with 
which it was mixed. 
Finally, the chromic acid solution was mixed with an 
excess of acetic acid, and the chromic acid thrown down by 
acetate of lead. 
A glance at the preceding table, shows clearly that no 
deduction can be drawn from the analyses which it exhibits, 
because the ore was never pure. There is reason to believe 
that, in most cases, it is mixed with more or less of octahedral 
iron ore, besides the earthy matter with which it is obviously 
contaminated. I therefore reduced a quantity of the Baltimore 
ore to a coarse powder, and picked out a number of the 
small octahedrons, which constituted the pure chromium 
ore. They had more or less of the form of octahedrons, a 
brown colour with a splendent and almost metallic lustre. 
The specific gravity was 4-321. All the particles the least 
