Potassium as an Oxydizing mixture. 199 
hydric acid, until chlorine ceased to be evolved, saturating the 
acid liquor with ammonia water, washing and drying the pre- 
cipitated hydrate and finally igniting it intensely in a platinum 
crucible over a blast-lamp. 
0-102 grm. of this anhydrous oxyd was placed in an evapo- 
rating dish, together with a quantity of nitric acid and some 
chlorate of potassium, and covered with an inverted funnel 
with a bent stem. The acid was heated and fragments of chlo- 
rate of potassium were added to it from time to time, until the 
chromic oxyd had completely disappeared. This result was 
attained in the course of half an hour 
he acid solution was diluted with water, then neutralized 
with ammonia and the ammoniacal solution in its turn treated 
with enough acetic acid to make it slightly acid. After the 
acidulated solution has become cold, a solution of chlorid of 
barium was added to it, in slight excess, and the mixture was 
left at rest for ten or twelve hours, The precipitated chromate 
of barium was washed, by decantation, with a cold solution of 
acetate of ammonium, then collected on a filter, rinsed with 
water, dried, heated in a crucible to expel the last traces of 
water and of the ammonium salt, and weighed. - 
The amount of chromate of barium obtained in this experi- 
ment was equal to 0°336 grm., which is equivalent to 68°31 per 
cent of chromium instead of 68°62 per cent as required by 
theory. 
The precipitate of chromate of barium must be allowed to 
stand for some time before filtering lest it pass through the pores 
of the filter and render the filtrate cloudy. 
‘The acetate of ammonium employed for washing serves to 
dissolve any nitrate of barium or chlorid of barium which may 
have been precipitated with the chromate. It has the further 
advantage of dissolving less of the chromate of barium than 
pure water would. iy 
I. A quantity of hydrate of chromium precipitated from a 
solution of reduced bichromate of potassium, as in the previous 
experiment, was dried at 115° and the proportion of water re- 
tained by the dried hydrate was determined once for all by ig- 
nition 
0-11 germ. of this dried hydrate, equal to 0-0688 of the an- 
hydrous oxyd, was then treated with nitric acid and chlorate 
of potassium as in experiment I. It was found that the oxyd- 
ation was completed as soon as the acid became hot enough to 
decompose the chlorate. Less than five minutes were sufficient 
in this instance for the complete conversion of the chromium to 
chromic acid, : 
The chromate of barium obtained weighed 02286 grm., equiv- 
