466 S. W. Johnson— Use of Potassium Dichromate. 
of purity and fine pulverization is, however, very tedious and 
laborious. I find that potassium dichromate mixed in suitable 
proportion with some infusible and indifferent body may be 
substituted for lead chromate, without detriment to the result, 
and with decided advantage in regard to cheapness and con- 
venience. 
My friend Mr. Geo. W. Hawes, on my suggestion, has made 
the experiments described below, and I take this occasion to 
express my thanks to him for the care and skill with which he 
has worked out the results. 
Potassium dichromate has nearly all the properties needful 
for an oxidant in organic analysis. It is found in commerce 
in a state of tolerable purity, and is readily and perfectly freed 
from objectionable admixtures by recrystallization and fusion 
at a low red heat. After fusion, it may be reduced to a moder- 
ately, but sufficiently fine powder with the greatest ease. When 
heated to bright redness, it gives off oxygen gas. 
perfection lies in its fluidity at the temperature suitable for 
combustion. 
Ordinary kaolin, or fire clay, is perhaps generally the cheapest 
material for diluting the potassium dichromate. The clay use 
in these experiments was nearly white and very fine, and was 
procured at a stove storein New Haven. Clay from the labora- 
tory stock was found useless from containing anthracite dust, » 
it having been kept for a long time poorly covered in our 
furnace room. 
The clean sifted clay, placed in a crucible, was first strongly 
ignited for half an hour in a charcoal fire. It was then mixe 
